Magnetic recording medium with multiple exchange coupling layers and small grain magnetic layers

According to one embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes five or more magnetic recording layers and four or more nonmagnetic exchange coupling layers, where the magnetic recording layers and the nonmagnetic exchange coupling layers are arranged in an alternating pattern, and where the magnetic recording layers are separated from each other by least one of the nonmagnetic exchange coupling layers. The magnetic recording layer positioned closest to the substrate has each of the following: an average magnetic grain pitch of about 8.3 nm or less, a magnetic anisotropy field (Hk) value of greater than or equal to about 20 kOe, and a thickness that is about 40% of a total thickness of the magnetic recording layer structure.

FIELD OF THE INVENTION

The present invention relates to magnetic recording media, and more specifically, this invention relates to a recording layer structure having small grain magnetic recording layers separated by exchange coupling layers, which may be of particular use in perpendicular magnetic recording (PMR) media, shingle-written magnetic recording (SMR) media, and magnetic field-assisted magnetic recording (MAMR) media.

BACKGROUND

The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.

The volume of information processing in the information age is increasing rapidly. Accordingly, an important and ongoing goal involves increasing the amount of information able to be stored in the limited area and volume of HDDs. Increasing the areal recording density of HDDs provides one technical approach to achieve this goal. In particular, reducing the size of recording bits and components associated therewith offers an effective means to increase areal recording density.

However, the continual push to miniaturize the recording bits and associated components presents its own set of challenges and obstacles. For instance, as the size of the ferromagnetic crystal grains in a magnetic recording layer become smaller and smaller, the crystal grains may become thermally unstable, such that thermal fluctuations result in magnetization reversal and the loss of recorded data. Increasing the magnetic anisotropy of the magnetic particles may improve the thermal stability thereof, yet ultimately reduce the ability to write information thereto. Accordingly, increasing the magnetic anisotropy of the magnetic particles may also require increasing the switching field needed to switch the magnetization of the magnetic particles during a write operation.

SUMMARY

According to one embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes: a first recording magnetic layer having a first magnetic anisotropy field (Hk) value greater than or equal to about 20 kOe; a first nonmagnetic exchange coupling layer formed above the first magnetic recording layer; a second magnetic recording layer formed above the first nonmagnetic exchange coupling layer, the second magnetic recording layer having a second Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a second nonmagnetic exchange coupling layer formed above the second magnetic recording layer; a third magnetic recording layer formed above the second nonmagnetic exchange coupling layer, the third magnetic recording layer having a third Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a third nonmagnetic exchange coupling layer formed above the third magnetic recording layer; a fourth magnetic recording layer formed above the third nonmagnetic exchange coupling layer, the fourth magnetic recording layer having a fourth Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a fourth nonmagnetic exchange coupling layer formed above the fourth magnetic recording layer; and a fifth magnetic recording layer formed above the fourth nonmagnetic exchange coupling layer, the fifth magnetic recording layer having a fifth Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer.

According to another embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes five or more magnetic recording layers and four or more nonmagnetic exchange coupling layers, where the magnetic recording layers and the nonmagnetic exchange coupling layers are arranged in an alternating pattern, and where the magnetic recording layers are separated from each other by least one of the nonmagnetic exchange coupling layers. The magnetic recording layer positioned closest to the substrate has each of the following: an average magnetic grain pitch of about 8.3 nm or less, a magnetic anisotropy field (Hk) value of greater than or equal to about 20 kOe, and a thickness that is about 40% of a total thickness of the magnetic recording layer structure.

Any of these embodiments may be implemented in a magnetic data storage system such as a disk drive system, which may include a magnetic head, a drive mechanism for passing a magnetic medium (e.g., hard disk) over the magnetic head, and a controller electrically coupled to the magnetic head.

DETAILED DESCRIPTION

The following description discloses several preferred embodiments of magnetic storage systems and/or related systems and methods, as well as operation and/or component parts thereof.

In one general embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes: a first recording magnetic layer having a first magnetic anisotropy field (Hk) value greater than or equal to about 20 kOe; a first nonmagnetic exchange coupling layer formed above the first magnetic recording layer; a second magnetic recording layer formed above the first nonmagnetic exchange coupling layer, the second magnetic recording layer having a second Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a second nonmagnetic exchange coupling layer formed above the second magnetic recording layer; a third magnetic recording layer formed above the second nonmagnetic exchange coupling layer, the third magnetic recording layer having a third Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a third nonmagnetic exchange coupling layer formed above the third magnetic recording layer; a fourth magnetic recording layer formed above the third nonmagnetic exchange coupling layer, the fourth magnetic recording layer having a fourth Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer; a fourth nonmagnetic exchange coupling layer formed above the fourth magnetic recording layer; and a fifth magnetic recording layer formed above the fourth nonmagnetic exchange coupling layer, the fifth magnetic recording layer having a fifth Hkvalue that is less than or about equal to the first Hkvalue of the first magnetic recording layer.

In another general embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes five or more magnetic recording layers and four or more nonmagnetic exchange coupling layers, where the magnetic recording layers and the nonmagnetic exchange coupling layers are arranged in an alternating pattern, and where the magnetic recording layers are separated from each other by least one of the nonmagnetic exchange coupling layers. The magnetic recording layer positioned closest to the substrate has each of the following: an average magnetic grain pitch of about 8.3 nm or less, a magnetic anisotropy field (Hk) value of greater than or equal to about 20 kOe, and a thickness that is about 40% of a total thickness of the magnetic recording layer structure.

Referring now toFIG. 1, there is shown a disk drive100in accordance with one embodiment of the present invention. As shown inFIG. 1, at least one rotatable magnetic medium (e.g., magnetic disk)112is supported on a spindle114and rotated by a drive mechanism, which may include a disk drive motor118. The magnetic recording on each disk is typically in the form of an annular pattern of concentric data tracks (not shown) on the disk112. The disk drive motor118preferably passes the magnetic disk112over the magnetic read/write portions121, described immediately below.

At least one slider113is positioned near the disk112, each slider113supporting one or more magnetic read/write portions121, e.g., of a magnetic head according to any of the approaches described and/or suggested herein. As the disk rotates, slider113is moved radially in and out over disk surface122so that portions121may access different tracks of the disk where desired data are recorded and/or to be written. Each slider113is attached to an actuator arm119by means of a suspension115. The suspension115provides a slight spring force which biases slider113against the disk surface122. Each actuator arm119is attached to an actuator127. The actuator127as shown inFIG. 1may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by controller129.

During operation of the disk storage system, the rotation of disk112generates an air bearing between slider113and disk surface122which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension115and supports slider113off and slightly above the disk surface by a small, substantially constant spacing during normal operation. Note that in some embodiments, the slider113may slide along the disk surface122.

The various components of the disk storage system are controlled in operation by control signals generated by controller129, such as access control signals and internal clock signals. Typically, control unit129comprises logic control circuits, storage (e.g., memory), and a microprocessor. In a preferred approach, the control unit129is electrically coupled (e.g., via wire, cable, line, etc.) to the one or more magnetic read/write portions121, for controlling operation thereof. The control unit129generates control signals to control various system operations such as drive motor control signals on line123and head position and seek control signals on line128. The control signals on line128provide the desired current profiles to optimally move and position slider113to the desired data track on disk112. Read and write signals are communicated to and from read/write portions121by way of recording channel125.

An interface may also be provided for communication between the disk drive and a host (integral or external) to send and receive the data and for controlling the operation of the disk drive and communicating the status of the disk drive to the host, all as will be understood by those of skill in the art.

In a typical head, an inductive write portion includes a coil layer embedded in one or more insulation layers (insulation stack), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write portion. The pole piece layers may be connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk.

The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium.

FIG. 2Ais a cross-sectional view of a perpendicular magnetic head200, according to one embodiment. InFIG. 2A, helical coils210and212are used to create magnetic flux in the stitch pole208, which then delivers that flux to the main pole206. Coils210indicate coils extending out from the page, while coils212indicate coils extending into the page. Stitch pole208may be recessed from the ABS218. Insulation216surrounds the coils and may provide support for some of the elements. The direction of the media travel, as indicated by the arrow to the right of the structure, moves the media past the lower return pole214first, then past the stitch pole208, main pole206, trailing shield204which may be connected to the wrap around shield (not shown), and finally past the upper return pole202. Each of these components may have a portion in contact with the ABS218. The ABS218is indicated across the right side of the structure.

Perpendicular writing is achieved by forcing flux through the stitch pole208into the main pole206and then to the surface of the disk positioned towards the ABS218.

FIG. 2Billustrates one embodiment of a piggyback magnetic head201having similar features to the head200ofFIG. 2A. As shown inFIG. 2B, two shields204,214flank the stitch pole208and main pole206. Also sensor shields222,224are shown. The sensor226is typically positioned between the sensor shields222,224.

FIG. 3Ais a schematic diagram of another embodiment of a perpendicular magnetic head300, which uses looped coils310to provide flux to the stitch pole308, a configuration that is sometimes referred to as a pancake configuration. The stitch pole308provides the flux to the main pole306. With this arrangement, the lower return pole may be optional. Insulation316surrounds the coils310, and may provide support for the stitch pole308and main pole306. The stitch pole may be recessed from the ABS318. The direction of the media travel, as indicated by the arrow to the right of the structure, moves the media past the stitch pole308, main pole306, trailing shield304which may be connected to the wrap around shield (not shown), and finally past the upper return pole302(all of which may or may not have a portion in contact with the ABS318). The ABS318is indicated across the right side of the structure. The trailing shield304may be in contact with the main pole306in some embodiments.

FIG. 3Billustrates another embodiment of a piggyback magnetic head301having similar features to the head300ofFIG. 3A. As shown inFIG. 3B, the piggyback magnetic head301also includes a looped coil310, which wraps around to form a pancake coil. Sensor shields322,324are additionally shown. The sensor326is typically positioned between the sensor shields322,324.

InFIGS. 2B and 3B, an optional heater is shown near the non-ABS side of the magnetic head. A heater (Heater) may also be included in the magnetic heads shown inFIGS. 2A and 3A. The position of this heater may vary based on design parameters such as where the protrusion is desired, coefficients of thermal expansion of the surrounding layers, etc.

FIG. 4provides a schematic diagram of a simplified perpendicular recording medium400, which may also be used with magnetic disk recording systems, such as that shown inFIG. 1. As shown inFIG. 4, the perpendicular recording medium400, which may be a recording disk in various approaches, comprises at least a supporting substrate402of a suitable non-magnetic material (e.g., glass, aluminum, etc.), and a soft magnetic underlayer404of a material having a high magnetic permeability positioned above the substrate402. The perpendicular recording medium400also includes a magnetic recording layer406positioned above the soft magnetic underlayer404, where the magnetic recording layer406preferably has a high coercivity relative to the soft magnetic underlayer404. There may one or more additional layers (not shown), such as an “exchange-break” layer or “interlayer”, between the soft magnetic underlayer404and the magnetic recording layer406.

The orientation of magnetic impulses in the magnetic recording layer406is substantially perpendicular to the surface of the recording layer. The magnetization of the soft magnetic underlayer404is oriented in (or parallel to) the plane of the soft underlayer404. As particularly shown inFIG. 4, the in-plane magnetization of the soft magnetic underlayer404may be represented by an arrow extending into the paper.

FIG. 5Aillustrates the operative relationship between a perpendicular head508and the perpendicular recording medium400ofFIG. 4. As shown inFIG. 5A, the magnetic flux510, which extends between the main pole512and return pole514of the perpendicular head508, loops into and out of the magnetic recording layer406and soft magnetic underlayer404. The soft magnetic underlayer404helps focus the magnetic flux510from the perpendicular head508into the magnetic recording layer406in a direction generally perpendicular to the surface of the magnetic medium. Accordingly, the intense magnetic field generated between the perpendicular head508and the soft magnetic underlayer404, enables information to be recorded in the magnetic recording layer406. The magnetic flux is further channeled by the soft magnetic underlayer404back to the return pole514of the head508.

As noted above, the magnetization of the soft magnetic underlayer404is oriented in (parallel to) the plane of the soft magnetic underlayer404, and may represented by an arrow extending into the paper. However, as shown inFIG. 5A, this in plane magnetization of the soft magnetic underlayer404may rotate in regions that are exposed to the magnetic flux510.

FIG. 5Billustrates one embodiment of the structure shown inFIG. 5A, where soft magnetic underlayers404and magnetic recording layers406are positioned on opposite sides of the substrate402, along with suitable recording heads508positioned adjacent the outer surface of the magnetic recording layers406, thereby allowing recording on each side of the medium.

Except as otherwise described herein with reference to the various inventive embodiments, the various components of the structures ofFIGS. 1-5B, and of other embodiments disclosed herein, may be of conventional material(s), design, and/or fabricated using conventional techniques, as would become apparent to one skilled in the art upon reading the present disclosure.

Referring now toFIG. 6, a perpendicular magnetic recording medium600comprising a recording layer structure having three exchange coupling layers is shown according to one embodiment. As an option, the perpendicular magnetic recording medium600may be implemented in conjunction with features from any other embodiment listed herein, such as those described with reference to the other FIGS. Of course, the perpendicular magnetic recording medium600and others presented herein may be used in various applications and/or in permutations which may or may not be specifically described in the illustrative embodiments listed herein. For instance, the perpendicular magnetic recording medium600may include more or less layers than those shown inFIG. 6, in various approaches. Moreover, unless otherwise specified, formation of one or more of the layers shown inFIG. 6may be achieved via atomic layer deposition (ALD), chemical vapor deposition (CVD), evaporation, e-beam evaporation, ion beam deposition, sputtering, or other deposition technique as would become apparent to a skilled artisan upon reading the present disclosure. Further, the perpendicular magnetic recording medium600and others presented herein may be used in any desired environment.

As shown inFIG. 6, the perpendicular magnetic recording medium600includes a substrate602comprising a material of high rigidity, such as glass, Al, Al2O3, AlMg, MgO, Si, or other suitable substrate material as would be understood by one having skill in the art upon reading the present disclosure. In some approaches, the substrate602may have a thickness that is greater than or less than the other layers formed thereon.

The perpendicular magnetic recording medium600also includes an adhesion layer604formed above the substrate602, the adhesion layer604being configured to improve adhesion between the substrate602and the layers deposited thereon. The adhesion layer604may also be configured to control the size of the magnetic grains in one or more of the layers of the magnetic recording layer structure624. In preferred approaches, the adhesion layer604comprises an amorphous material that does not affect the crystal orientation of the layers deposited thereon. Suitable materials for the adhesion layer604include, but are not limited to, Ni, Co, Al, Ti, Cr, Zr, Ta, Nb and combinations and/or alloys thereof.

The perpendicular magnetic recording medium600additionally includes a soft magnetic underlayer structure606formed above the adhesion layer604, the soft magnetic underlayer structure606being configured to promote data recording in one or more of the magnetic recording layers of the magnetic recording layer structure624by suppressing the spread of the magnetic field and efficiently magnetizing the one or more magnetic recording layers. As shown inFIG. 6, the soft magnetic underlayer structure606includes a first soft magnetic underlayer608and a second soft magnetic underlayer612separated by an anti-ferromagnetic coupling (AFC) layer610, typically of Ru or other AFC material as known in the art. The first and second soft magnetic underlayers608,612may each independently be comprised of cobalt, iron, tantalum, zirconium, nickel, boron, chromium, or compositions thereof, etc., which preferably provide a high moment.

An exchange break layer structure614is formed above the soft magnetic underlayer structure606, the exchange break layer structure614being configured to control the grain size and crystalline orientation of the layers formed thereabove, as well as magnetically decouple the magnetically permeable layers of the soft magnetic underlayer structure606and the magnetic recording layers of the magnetic recording layer structure624. As shown inFIG. 6, the exchange break layer structure614includes a first exchange break layer616, also referred to herein as a seed layer. The first exchange break layer616may include at least one of Ni, Cu, Pd, Pt, Cr, W, V, Mo, Ta, Nb, Fe, and other suitable materials as would become apparent to one skilled in the art upon reading the present disclosure.

The exchange break layer structure614also includes a second exchange break layer618formed above the first exchange break layer616, and a third exchange break layer620formed above the second exchange break layer618, where the second and third exchange break layers may also be referred to herein as underlayers. The second and third exchange break layers618,620may include one or more materials having a hexagonal close packed (hcp) crystalline structure, such as Ru, or other such suitable material as would become apparent to one having skill in the art upon reading the present disclosure. In various approaches, the second and third exchange break layers618,620may be formed under different gas pressures during sputtering, such as a lower pressure for the second exchange break layer618, and higher pressures for the third exchange break layer620.

The exchange break layer structure614further includes a fourth exchange break layer622, which may be referred to herein as an onset layer, formed above the third exchange break layer620. Suitable materials for the fourth exchange break layer622may include ruthenium, titanium, tantalum, and/or oxides thereof, etc.

As shown inFIG. 6, the magnetic recording layer structure624is formed above the exchange break layer structure614, the magnetic recording layer structure624having four magnetic recording layers626,630,634,638and three exchange coupling layers628,632,636. In the embodiment depicted inFIG. 6, the magnetic recording layer structure624includes an alternating pattern of magnetic recording layers and exchange coupling layers. For instance, the magnetic recording layer structure624includes the first magnetic recording layer626, the first exchange coupling layer628formed above the first magnetic recording layer626, the second magnetic recording layer630formed above the first exchange coupling layer628, the second exchange coupling layer632formed above the second magnetic recording layer630, the third magnetic recording layer634formed above the second exchange coupling layer632, the third exchange coupling layer636formed above the third magnetic recording layer634, and the fourth magnetic recording layer638(also referred to as the cap layer638) formed above the third exchange coupling layer636.

The three lowermost magnetic recording layers626,630,634in the magnetic recording layer structure624each include a plurality of grains separated from one another via a segregant material. Illustrative materials for one or more of the magnetic recording layers626,630,634may include CoCrPtX+oxide and/or O2, where X denotes one or more optional alloying elements such as B, Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may be TiOx, SiOx, B2O3, W2O5, Ta2O5, NbO2, CoO, Co3O4, etc.

The thickness of the first magnetic recording layer626may typically be in a range from 4 nm to 5.5 nm. It has been found that for magnetic recording layer structures having four magnetic recording layers and three exchange coupling layers, such as the magnetic recording layer structure624shown inFIG. 6, increasing the thickness of the lowermost magnetic recording layer (see e.g., the first magnetic recording layer626) above 5.5 nm substantially reduces or completely precludes media writeability.

With continued reference toFIG. 6, the thicknesses of the second and third magnetic recording layers630,634may each independently be in a range from 0.5 nm to about 3 nm in various approaches. In some approaches, the second and third magnetic recording layers630,634may have a thickness that is the same or different from one another. In one particular approach, the thickness of the second magnetic recording layer630may be about 2.8 nm, and the thickness of the third magnetic recording layer634may be about 1.2 nm.

In various approaches, the magnetic anisotropy, Ku, of the first magnetic recording layer626may be greater than the Kuof the second magnetic recording layer630. In more approaches, the magnetic anisotropy, Ku, of the first magnetic recording layer626may be greater than the Kuof the second magnetic recording layer630and the Kuof the third magnetic recording layer634. In yet more approaches where the Kuvalues of the first and third magnetic recording layers626,634are greater than the Kuof the second magnetic recording layer630, the Kuof the first magnetic recording layer626may be greater than or about equal to the Kuof the third magnetic recording layer634.

As noted previously, the magnetic recording layer structure624includes three exchange coupling layers628,632,636configured to magnetically decouple the magnetic recording layers626,630,634,638, as well as promote the grain growth and crystalline orientation of the layers formed thereabove. Each of the exchange coupling layers628,632,636may include a plurality of grains separated from one another via a segregant material. Moreover, each of the exchange coupling layers628,632,636are preferably nonmagnetic.

In preferred approaches, one or more of the exchange coupling layers628,632,636may include one or more of the same materials as one or more of the magnetic recording layers626,630,634, though not necessarily in the same stoichiometric proportions given that the exchange coupling layers628,632,636are preferably nonmagnetic. For instance, in one preferred approach, one or more of the exchange coupling layers628,632,636may include CoCrPtX+oxide and/or O, where X denotes one or more optional alloying elements such as B, Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may be TiOx, SiOx, B2O3, W2O5, Ta2O5, NbO2, CoO, Co3O4, etc.

In various approaches, the thicknesses of the exchange coupling layers628,632,636, may each independently be in a range from 0.5 nm to 2 nm. In some approaches, some or all of the exchange coupling layers628,632,636may have thicknesses that are the same or different relative to one another.

As additionally shown inFIG. 6, the fourth magnetic recording layer638, also referred to as a cap layer, is the uppermost layer in the magnetic recording layer structure624. Suitable materials for the cap layer638may include, but are not limited to, a Co—, CoCr—, CoPtCr—, and/or CoPtCrB— based alloy, or other such material as would become apparent to one having skill in the art upon reading the present disclosure. In various approaches, the cap layer638may be a continuous cap layer. In some approaches, the cap layer638may be a continuous, partially oxidized cap layer formed by flowing a mixture of oxygen and argon to distribute the oxygen in the cap layer. In particular approaches, the cap layer638may be formed at a lower argon pressure than all other magnetic recording layers positioned therebelow, thus forming a cap layer that is continuous, or at least more continuous than all other magnetic recording layers in the magnetic recording layer structure624.

As also shown inFIG. 6, a protective overcoat layer640is formed above the cap layer638. Suitable materials for the overcoat layer640may include, but are not limited to, diamond-like carbon, carbon nitride, Si-nitride, BN or B4C, etc.

An optional lubricant layer (not shown inFIG. 6) may be formed above the protective overcoat layer640. Suitable materials for the optional lubricant layer may also include, but are not limited to, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acids, etc.

As noted previously, efforts are continually made to increase the areal recording density of magnetic media. Areal density, e.g., as measured in bits per square inch, may be defined as the product of the track density (the tracks per inch radially on the magnetic medium, such as a disk) and the linear density (the bits per inch along each track). For a disk, the bits are written closely-spaced to form circular tracks on the disk surface, where each of the bits may comprise an ensemble of magnetic grains.

An important factor relevant to track density is the magnetic core width (MCW). The magnetic core width corresponds to the width of a magnetic bit recorded by the write pole of the write head. Thus, the smaller the magnetic core width, the greater the number of tracks of data that can be written to the media. Stated another way, high track density is associated with a narrow magnetic core width.

Moreover, an important factor relevant to linear density is the signal to noise ratio (SNR). Typically, a higher signal to noise ratio corresponds to a higher readable linear density. One approach to increase the signal to noise ratio involves reducing the size of the magnetic grains included within a magnetic recording layer. For instance, to support an areal density of 1 Tbit/in2 or more, the magnetic grain size needs to be reduced down to about an 8 nm pitch level. However, reducing the size of the magnetic grains may affect their thermal stability, represented as: KuV/kBT, where Kudenotes the magnetocrystalline anisotropy, V is the average grain volume, kBdenotes the Boltzmann constant, and T denotes the absolute temperature. To avoid thermal decay, KuV/kBT should be greater than or equal to about 60, and is preferably greater than or equal to about 80.

To compensate for the reduction in volume, V, of the magnetic grains, the magnetic anisotropy (Ku) of the magnetic grains may be increased to maintain thermal stability. For instance, in one approach, a high Kuportion of a magnetic recording layer structure, which may typically be the lowermost portion of the magnetic recording layer structure (see e.g., the high Kumagnetic recording layer626shown inFIG. 6), may be increased (e.g., the thickness of the high Kuportion may be increased) to maintain thermal stability of the magnetic grains therein. However, such an increase in this high Kuportion of a magnetic recording layer structure may decrease the media writeability (i.e., the ease at which information may be recording in the magnetic material).

Various embodiments disclosed herein overcome such drawbacks by providing perpendicular magnetic storage media comprising novel magnetic recording layer structures having at least five magnetic recording layers and at least four exchange coupling layers. In preferred approaches, the lowermost magnetic recording layer in these novel magnetic recording layer structures has a high magnetic anisotropy (e.g., a magnetic anisotropy field, Hk, greater than or equal to about 20 kOe), a film thickness greater than or equal to about 6 nm, preferably in a range from about 6 nm to about 8 nm, and an average grain pitch of about 8.3 nm or less, thus leading to small, yet thermally stable magnetic grains. Moreover, it has been surprisingly and unexpectedly found that these novel magnetic recording layer structures having at least five magnetic recording layers and at least four exchange coupling layers exhibit improved magnetic recording characteristics (e.g., signal-to-noise ratio (SNR), overwrite (OW), magnetic core width (MCW), etc.) as compared to magnetic recording layer structures having no more than four magnetic recording layers and no more than three exchange coupling layers (e.g., as shown inFIG. 6). The superior magnetic recording characteristics, such as the OW, exhibited by these novel magnetic recording layer structures is indeed surprising and unexpected given the overall increase in the thickness of said magnetic recording layer structures (e.g., via addition of at least one additional magnetic recording layer and at least one additional exchange coupling layer, and incorporation of a thick, high Kulowermost magnetic recording layer).

In more approaches, superior magnetic recording characteristics (e.g., SNR, OW, MCW, etc.) may also be achieved in approaches where these novel magnetic recording structures, e.g., those having at least five magnetic recording layers and at least four exchange coupling layers, are formed above an antiferromagnetically-coupled soft magnetic underlayer structure having a thickness less than or equal to about 35 nm, preferably less than or equal to about 25 nm. In yet more approaches, superior magnetic recording characteristics may additionally be achieved in approaches where these novel magnetic recording structures are formed above, and preferably directly on, an exchange break layer structure having a thickness less than or equal to about 15 nm.

Referring now toFIGS. 7A-7B, perpendicular magnetic recording media700,701each comprising a recording layer structure having at least four exchange coupling layers are shown according to one embodiment. As an option, the perpendicular magnetic recording media700,701may be implemented in conjunction with features from any other embodiment listed herein, such as those described with reference to the other FIGS. Of course, the perpendicular magnetic recording media700,701and others presented herein may be used in various applications and/or in permutations which may or may not be specifically described in the illustrative embodiments listed herein. For instance, the perpendicular magnetic recording media700,701may include more or less layers than those shown inFIGS. 7A-7B, in various approaches. Moreover, unless otherwise specified, formation of one or more of the layers shown inFIGS. 7A-7Bmay be achieved via atomic layer deposition (ALD), chemical vapor deposition (CVD), evaporation, e-beam evaporation, ion beam deposition, sputtering, or other deposition technique as would become apparent to a skilled artisan upon reading the present disclosure. Further, the perpendicular magnetic recording media700,701and others presented herein may be used in any desired environment.

As shown inFIG. 7A, the perpendicular magnetic recording medium700includes a substrate702comprising a material of high rigidity, such as glass, Al, Al2O3, AlMg, MgO, Si, or other suitable substrate material as would be understood by one having skill in the art upon reading the present disclosure. In some approaches, the substrate702may have a thickness that is greater than or less than the other layers formed thereon.

The perpendicular magnetic recording medium700also includes an adhesion layer704formed above the substrate702. The adhesion layer704is configured to improve adhesion between the substrate702and the layers deposited thereon. The adhesion layer704may also be configured to control the size of the magnetic grains in one or more of the layers of the magnetic recording layer structure724. In preferred approaches, the adhesion layer704comprises an amorphous material that does not affect the crystal orientation of the layers deposited thereon. Suitable materials for the adhesion layer704include, but are not limited to, Ni, Co, Al, Ti, Cr, Zr, Ta, Nb and combinations and/or alloys thereof. In particular approaches, the adhesion layer704may include at least one of TiAl, NiTa, TiCr, AlCr, NiTaZr, CoNbZr, TiAlCr, NiAlTi, CoAlTi, etc., or other suitable material as would become apparent to one having skill in the art upon reading the present disclosure. In more approaches, a thickness of the adhesion layer704may be in a range from about 1 nm to about 30 nm; however, as with any range pertaining to features shown inFIGS. 7A-7B, the upper and lower values could be higher or lower in various other approaches. In one preferred approach, the thickness of the adhesion layer704may be about 1.5 nm.

The perpendicular magnetic recording medium700additionally includes a soft magnetic underlayer structure706. The soft magnetic underlayer structure706is configured to promote data recording in one or more of the magnetic recording layers of the magnetic recording layer structure724by suppressing the spread of the magnetic field and efficiently magnetizing the one or more magnetic recording layers. As shown inFIG. 7A, the soft magnetic underlayer structure706includes a coupling layer710sandwiched between a first soft magnetic underlayer708and a second soft magnetic underlayer712, where the coupling layer710is configured to induce an anti-ferromagnetic coupling between the first and second soft magnetic underlayers708,712.

In various approaches, the first and/or second soft magnetic underlayers708,712include one or more materials having a high magnetic permeability. Accordingly, suitable materials for the first and/or the second soft magnetic underlayers708,712include, but are not limited to, amorphous alloys including Co and/or Fe as the main component(s), with at least one of: Ta, Hf, Nb, Si, Zr, B, C, Cr, Ni, etc. added thereto. Illustrative examples of suitable materials for the first and/or the second soft magnetic underlayers708,712may include CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoTaZr, CoFeTa, CoFeTaZr, CoFeB, CoZrNb, etc. Suitable materials for the coupling layer710include at least one of Ru, Ir, Cr, and other anti-ferromagnetic coupling materials as would become apparent to one skilled in the art upon reading the present disclosure.

The optimum thickness of the soft magnetic underlayer (SUL) structure706may depend on the material(s) of the first and second soft magnetic underlayers708,712and/or the coupling layer710, the structure and material(s) of the magnetic head configured to apply a magnetic field to the perpendicular magnetic recording medium700, and/or the distance between the soft magnetic underlayer structure706and the magnetic recording layer structure724, in various approaches. However, in some approaches, a total thickness, tsul, of the soft magnetic underlayer structure706may be in a range from about 10 nm to about 50 nm, preferably in a range from about 12 nm to about 35 nm, even more preferably in a range from about 12 nm to about 15 nm. In more approaches, a thickness of the first soft magnetic underlayer708may be in a range from about 5 nm to about 25 nm. In yet more approaches, a thickness of the second soft magnetic underlayer712may be in a range from about 5 nm to about 25 nm. In still more approaches, a thickness of the coupling layer710may be in a range from about 0.5 nm to about 2 nm.

As further shown inFIG. 7A, the perpendicular magnetic recording medium700includes an exchange break layer (EBL) structure714positioned above the soft magnetic underlayer structure706. The exchange break layer structure714is configured to magnetically decouple the magnetically permeable layers of the soft magnetic underlayer structure706and the magnetic recording layers of the magnetic recording layer structure724. The exchange break layer structure714is also configured to control the grain size and crystalline orientation of the layers formed thereabove.

In various approaches, the exchange break layer structure714may include one or more layers. For example, in the embodiment depicted inFIG. 7A, the exchange break layer structure714may include at least four separate exchange break layers. In various approaches, a total thickness, tebl, of the exchange break layer structure714may be less than or equal to about 15 nm.

The first exchange break layer716, also referred to herein as the seed layer, is configured to control the size of the magnetic grains in one or more of the layers of the magnetic recording layer structure724. In some approaches, the first exchange break layer716may include one or more nonmagnetic materials having a face centered cubic (fcc) crystalline structure. In particular approaches, the first exchange break layer716may include at least one of Ni, Cu, Pd, Pt, Cr, W, V, Mo, Ta, Nb, Fe, and other suitable materials as would become apparent to one skilled in the art upon reading the present disclosure. In more approaches, the first exchange break layer716may not include an oxide. In further approaches, the first exchange break layer716may have a thickness in a range from about 2 nm to about 8 nm.

The exchange break layer structure714also includes a second exchange break layer718formed above the first exchange break layer716, and a third exchange break layer720formed above the second exchange break layer718, where the second and third exchange break layers may also be referred to herein as underlayers. In various approaches, the second and/or third exchange break layers718,720may be configured to control the crystalline orientation of the layers formed thereabove, particularly one or more of the layers of the magnetic recording layer structure724. For instance, in one particular approach, the second and/or third exchange break layers718,720may include one or more materials having a hexagonal close packed (hcp) crystalline structure that promotes the epitaxial growth of one or more of the layers of the magnetic recording layer structure724such that the c-axis of said layers is oriented substantially perpendicular to the upper surface thereof, thus resulting in perpendicular magnetic anisotropy.

In a preferred approach, the second and/or third exchange break layers718,720may include Ru. In an even more preferred approach, the second and third exchange break layers718,720may include Ru formed under different gas pressures during sputtering, e.g., a lower pressure for the second exchange break layer718, and a higher pressure for the third exchange break layer720. In additional approaches, the second and/or third exchange break layers718,720may include Ru and a small amount of one or more of Ti, Ta, B, Cr or Si.

In more approaches, a thickness of the second and/or third exchange break layers718,720may be in a range from about 3 nm to about 10 nm.

The exchange break layer structure714additionally includes a fourth exchange break layer722formed above the third exchange break layer720. The fourth exchange break layer722may also be referred to herein as an onset layer. In various approaches, the fourth exchange break layer722may be configured to control the crystalline orientation and/or to promote the separation of the magnetic grains in one or more layers of the magnetic recording layer structure724. In some approaches, the fourth exchange break layer722may also include one or more materials having a hexagonal close packed (hcp) crystalline structure, such as Ru. In preferred approaches, the fourth exchange break layer722may include Ru and at least one oxide, such as TiO2, Ti2O5, WO3, W2O5, Ta2O5, SiO2, B2O3, etc. In more approaches, the fourth exchange break layer722may include Ru, at least one oxide, and a small amount of one or more of Ti, Ta, B, Cr and Si.

In further approaches, a thickness of the fourth exchange break layer722may be in a range from about 0.5 nm to about 2.0 nm. In numerous approaches, the fourth exchange break layer722may be substantially thinner than the second and/or third exchange break layers718,720.

As shown inFIG. 7A, the perpendicular magnetic recording medium700includes a magnetic recording layer structure724formed above the exchange break layer structure714. In various approaches, the magnetic recording layer structure724may include one or more magnetic recording layers and one or more exchange coupling layers. For example, in the embodiment depicted inFIG. 7A, the magnetic recording layer structure724may include at least five magnetic recording layers726,730,734,738,744, and at least four exchange coupling layers728,732,736,740. In such an embodiment, the magnetic recording layer structure724includes an alternating pattern of magnetic recording layers and exchange coupling layers. As particularly shown inFIG. 7A, the magnetic recording layer structure724includes the first magnetic recording layer726, the first exchange coupling layer728formed above the first magnetic recording layer726, the second magnetic recording layer730formed above the first exchange coupling layer728, the second exchange coupling layer732formed above the second magnetic recording layer730, the third magnetic recording layer734formed above the second exchange coupling layer732, the third exchange coupling layer736formed above the third magnetic recording layer734, the fourth magnetic recording layer738formed above the third exchange coupling layer736, the fourth exchange coupling layer740formed above the fourth magnetic recording layer738, and the fifth magnetic recording layer744(also referred to as the cap layer744) formed above the fourth exchange coupling layer740.

In some approaches, a total thickness, tmrl, of the magnetic recording layer structure724may be in a range from about 12 nm to about 20 nm. In more approaches, the magnetic recording layer structure724has a thermal stability factor (KuV/kBT) of greater than or equal to about 80.

The four lowermost magnetic recording layers726,730,734,738in the magnetic recording layer structure724may each include a plurality of grains separated from one another via a segregant material. In various approaches, the grains of one or more of the magnetic recording layers726,730,734,738may include one or more of Co, Cr, Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, Pd. In more approaches, the segregant material of one or more or the magnetic recording layers726,730,734,738may include O and/or at least one oxide of Ta, W, Nb, V, Mo, B, Si, Co, Cr, Ti, or Al. In one particular approach, one or more of the magnetic recording layers726,730,734,738may include CoCrPtX+oxide and/or O, where X may be B, Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may be TiOx, SiOx, B2O3, W2O5, Ta2O5, NbO2, CoO, Co3O4, etc. A magnetic recording layer having grains separated by an oxide segregant may be referred to herein as an oxide magnetic recording layer.

In various approaches, the average center-to-center spacing (pitch) of the grains in the magnetic recording layer structure724may be less than or equal to about 8.3 nm. In further approaches, the average grain size in the magnetic recording layer structure724may be in a range from about 6 nm to about 8.5 nm.

In some approaches, a thickness of the first magnetic recording layer726may be greater than or equal to about 5 nm. In particular approaches, a thickness of the first magnetic recording layer726may be in a range from about 5 nm to about 8 nm, preferably in a range from about 6 nm to about 7 nm. In other approaches, a thickness of the first magnetic recording layer726may be greater than or about equal to 40% of the total thickness of the magnetic recording layer structure724.

In more approaches, the thicknesses of the second, third and fourth magnetic recording layers730,734,738may each independently be in a range from 0.5 nm to about 3 nm. In some approaches, some or all of the second, third and fourth magnetic recording layers730,734,738may have thicknesses that are the same or different as one another. However, in preferred approaches, a thickness of one or more of the second, third, and fourth magnetic recording layers730,734,738may be about 1 nm.

In preferred approaches, the magnetic anisotropy energy, Ku, of the first magnetic recording layer726may be greater than or about equal to the Kuof the second magnetic recording layer730and/or the Kuof third magnetic recording layer734. For instance, in one approach, the magnetic anisotropy field, Hk, of the first magnetic recording layer726may be greater than or equal to about 20 kOe. In more approaches, the Hkof the second magnetic recording layer730and/or third magnetic recording layer734may be in a range from 15 kOe to 20 kOe.

In yet more approaches, the Kuof the fourth magnetic recording layer738may also be greater than or about equal to the Kuof the second magnetic recording layer730and/or the Kuof the third magnetic recording layer734. In still more approaches, the Kuof the fourth magnetic recording layer738may be about equal to or less than the Kuof the first magnetic recording layer726. In particular approaches, the Hkof the fourth magnetic recording layer738may be in a range from 15 kOe to 22 kOe.

As noted above, the second and third magnetic recording layers730,734may each have a Kuthat is less than the Kuvalues of the first and/or fourth magnetic recording layers726,738in some approaches. Accordingly, in approaches where the first, second, third and fourth magnetic recording layers726,730,734,738comprise CoCrPt+O2and/or oxide, the second and third magnetic layers730,734may each comprise a higher percentage of at least one of Cr, O2and/or the oxide (e.g., TiOx, SiOx, B2O3, W2O5, Ta2O5, NbO2, CoO, Co3O4, etc.), and other non-magnetic materials (e.g., Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc.,) to reduce their respective Kuvalues compared to the Kuvalues of the first and/or fourth magnetic recording layers726,738. Moreover, it is important to note that while the second and third magnetic recording layers730,734may each have a Kuthat is less than the Kuvalues of the first and/or fourth magnetic recording layers726,738in some approaches, the Kuvalues of the second and third magnetic recording layers730,734may, but need not, be equal. For instance, the Kuof the second magnetic recording layer730may be greater than, equal to, or less than the Kuof the third magnetic recording layer734in further approaches.

A summary of some of the possible relationships between the Hkvalues of the first magnetic recording layer726(Hk1), the second magnetic recording layer730(Hk2), the third magnetic recording layer734(Hk3) and the fourth magnetic recording layer738(Hk4) may be represented as follows:

As noted above, the magnetic recording layer structure724ofFIG. 7Aincludes at least four exchange coupling layers728,732,736,740. The exchange coupling layers728,732,736,740are configured to magnetically decouple the magnetic recording layers726,730,734,738, as well as promote the grain growth and crystalline orientation of the layers formed thereabove.

In various approaches, the exchange coupling layers728,732,736,740are positioned in an upper portion742of the magnetic recording layer structure724, wherein a thickness of the upper portion742may be less than or about equal to 60% of the total thickness, tmrl, of the magnetic recording layer structure724.

Each of the exchange coupling layers728,732,736,740may include a plurality of grains separated from one another via a segregant material. In numerous approaches, the grains of one or more of the exchange coupling layers728,732,736,740may include one or more of the same materials (e.g., Co, Cr, Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, Pd, etc.) included in the grains of one or more of the magnetic recording layers726,730,734,738. In additional approaches, the segregant material of one or more of the exchange coupling layers728,732,736,740may include one or more of the same materials (e.g., O2, at least one oxide of Ta, W, Nb, V, Mo, B, Si, Co, Cr, Ti, Al, etc.) included in the segregant material of one or more of the magnetic recording layers726,730,734,738. An exchange coupling layer having grains separated by an oxide segregant may be referred to herein as an oxide exchange coupling layer.

It is important to note that each of the exchange coupling layers728,732,736,740are preferably nonmagnetic, e.g., have a saturation magnetization, Ms, less than or equal to about 100 emu/cc. Thus, one or more of the exchange coupling layers728,732,736,740may include one or more of the same materials as one or more of the magnetic recording layers726,730,734,738, though not necessarily in the same stoichiometric proportions. For example, in some approaches, at least one of the exchange coupling layers and at least one of the magnetic recording layers may include CoCrPtX+O and/or oxide, where X may be Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may include one or more of TiOx, SiOx, B2O3, W2O5, Ta2O5, NbO2, CoO, Co3O4, etc.; however, the amount of Co in the exchange coupling layer may be less than the amount of Co in the magnetic recording layer. Further, an amount of Co in the first magnetic recording layer726is greater than or about equal to the Co amount in the second, third and fourth magnetic recording layers730,734, and738.

In various approaches, the thicknesses of the exchange coupling layers728,732,736,740may each independently be in a range from about 0.5 nm to about 2 nm. In some approaches, some or all of the exchange coupling layers728,732,736,740may have thicknesses that are the same or different as one another. For instance, in particular approaches, the thickness of the second exchange coupling layer732may be less than, equal to, or greater than the thickness of third exchange coupling layer736.

In more approaches, the thickness of the second exchange coupling layer732may be greater than the thickness of the first exchange coupling layer728and/or the thickness of the fourth exchange coupling layer740. In yet more approaches, the thickness of the third exchange coupling layer736may be greater than the thickness of the first exchange coupling layer728and/or the thickness of the fourth exchange coupling layer740. In still more approaches, the thickness of the first exchange coupling layer728may be less than the thicknesses of all other exchange coupling layers. In still more approaches, the thickness of the first exchange coupling layer728may be about equal to the thickness of the fourth exchange coupling layer740. In one preferred approach, the thickness of the first exchange coupling layer728may be about 0.6 nm; the thickness second exchange coupling layer732may be about 1 nm; the thickness of the third exchange coupling layer736may be about 1 nm; and the thickness of the fourth exchange coupling layer740may be about 0.7 nm.

In further approaches, grains in the magnetic recording layers726,730,734,738and the exchange coupling layers728,732,736,740may have a columnar shape. Moreover, the grains in each of the magnetic recording layers726,730,734,738and the exchange coupling layers728,732,736,740may be physically characterized by growth directly on the grains present in the layers thereabove and/or therebelow. For instance, each of the grains in the fourth exchange coupling layer740may be formed directly on the grains in the fourth magnetic recording layer738, which in turn may be formed directly on the grains in the third exchange coupling layer736and so on.

It is important to note that while the magnetic recording layer structure724ofFIG. 7Aincludes five magnetic recording layers726,730,734,738,744and four exchange coupling layers728,732,736,740, the magnetic recording layer structure724may include one or more additional magnetic recording layers and one or more additional exchange coupling layers in various approaches. For instance, as shown inFIG. 7B, a perpendicular magnetic recording medium701may include a magnetic recording layer structure748having six or more magnetic recording layers and five or more exchange coupling layers, where the magnetic recording layers and the exchange coupling layers are arranged in an alternating pattern. AsFIG. 7Bdepicts one exemplary variation of the perpendicular magnetic recording medium700ofFIG. 7A, components and layers ofFIG. 7Bhave common numbering with those ofFIG. 7A. It is important to note, however, that the fifth magnetic recording layer744shown inFIG. 7A, is represented as the sixth magnetic recording layer744inFIG. 7B.

With continued reference toFIG. 7A, the fifth magnetic recording layer744(also referred to as the cap layer744) may form the uppermost layer in the magnetic recording layer structure724. Suitable materials for the fifth magnetic recording layer (cap layer)744may include, but are not limited to, a Co—, CoCr—, CoPtCr—, and/or CoPtCrB— based alloy, or other such material as would become apparent to one having skill in the art upon reading the present disclosure. In various approaches, the fifth magnetic recording layer (cap layer)744may be a continuous cap layer that does not include a segregant material. For instance, in one approach, the fifth magnetic recording layer (cap layer)744may not include any oxides. In some approaches, the fifth magnetic recording layer (cap layer)744may be doped with a small amount of oxygen. For example, in particular approaches, the fifth magnetic recording layer (cap layer)744may be a continuous, partially oxidized cap layer formed at a lower argon pressure than all other magnetic recording layers positioned therebelow, thus forming a cap layer that is continuous, or at least more continuous than all other magnetic recording layers in the magnetic recording layer structure724.

In more approaches, a thickness of the fifth magnetic recording layer (cap layer)744may be in a range from about 2 nm to about 5 nm. In preferred approaches the thickness of the fifth magnetic recording layer (cap layer)744may be about 3 nm. In yet more approaches, the fifth magnetic recording layer (cap layer)744may comprise multiple layers configured to achieve ideal separation, magnetics and smoothness.

In additional approaches, the magnetic anisotropy energy, Ku, of the fifth magnetic recording layer (cap layer)744may be less than or about equal to the Kuof the first and/or fourth magnetic recording layers726,736. Moreover, while the second, third, and fifth magnetic recording layers730,734,744may each have a Kuthat is less than the Kuvalues of the first and/or fourth magnetic recording layers726,738in some approaches, the Kuvalues of the second, third and fifth magnetic recording layers730,734,744may, but need not, be equal. For instance, the Kuof the fifth magnetic recording layer730may be greater than, equal to, or less than the Kuof the second and/or third magnetic recording layers730,734in further approaches. In particular approaches, the Hkof the fifth magnetic recording layer (cap layer)744may be in a range from 10 kOe to 18 kOe.

As shown inFIG. 7A, a protective overcoat layer746is formed above the fifth magnetic recording layer (cap layer)744. The protective overcoat layer may be configured to protect the underlying layers from wear, corrosion, etc. This protective overcoat layer may be made of, for example, diamond-like carbon, carbon nitride, Si-nitride, BN or B4C, etc, or other such materials suitable for a protective overcoat as would become apparent to one having skill in the an upon reading the present disclosure.

In additional approaches, an optional lubricant layer (not shown inFIG. 7A) may be formed above the protective overcoat layer746. The material of the lubricant layer may include, but is not limited to perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acids, etc., or other suitable lubricant material as known the art.

As is described in greater detail below, it has been surprisingly and unexpectedly found that the perpendicular magnetic recording medium700having at least five magnetic recording layers726,730,734,738,744and at least four exchange coupling layers728,732,736,740exhibits improved magnetic recording characteristics (e.g., signal-to-noise ratio (SNR), overwrite (OW), magnetic core width (MCW), etc.) as compared to a perpendicular magnetic recording medium having four or less magnetic recording layers and three or less exchange coupling layers (e.g., as shown inFIG. 6). The improvement in the magnetic recording characteristics, such as the OW, for the perpendicular magnetic recording medium700ofFIG. 7is indeed surprising and unexpected given the increase in overall thickness of the magnetic recording layer structure724(e.g., via addition of at least one additional magnetic recording layer and at least one addition exchange coupling layer, and incorporation of a thicker, high Kulowermost magnetic recording layer) relative to the magnetic recording layer structure624of the perpendicular magnetic recording medium600shown inFIG. 6. Rather, one skilled in the art would typically expect that increasing the thickness of the lowermost, high Kumagnetic recording layer, and/or adding at least one more magnetic recording layer and at least one more exchange coupling layer, both of which ultimately increase the distance between the magnetic head and the lowermost magnetic recording layer, would actually degrade media writeability.

Experimental Data and Comparative Examples

The following experimental data describe features and/or characteristics associated with the novel perpendicular magnetic storage media disclosed herein, particularly those having a magnetic recording layer structure comprising five magnetic recording layers and four exchange coupling layers as shownFIG. 7A. A perpendicular magnetic recording medium having a magnetic recording layer structure with five magnetic recording layers and four exchange coupling layers may be referred to as a “quad ECL structure” or “Q-ECL” for clarity.

Comparative examples are also provided to illustrate the differences between quad ECL structures and triple ECL (T-ECL) structures (i.e., perpendicular magnetic recording media having a magnetic recording structure with four magnetic recording layers and three exchange coupling layers as shownFIG. 6).

Also for clarity, the lowermost magnetic recording layer in a quad ECL structure (e.g., the first magnetic recording layer726shown inFIG. 7A) may be referred to as the “G0” layer, whereas the lowermost magnetic recording layer in a triple ECL structure (e.g., the first magnetic recording layer626shown inFIG. 6) may be referred to as the “G1” layer. Additionally, the media grain pitch in a quad or triple ECL structure corresponds to the average grain pitch in the magnetic recording layer structure present therein (e.g., the magnetic recording layer structure724shown inFIG. 7Afor the quad ECL structure; and the magnetic recording layer structure624shown inFIG. 6for the triple ECL structure).

It is important to note that the experimental data and comparative examples do not limit the invention in anyway.

FIGS. 8-12provide plots illustrating the relationship between various measured magnetic characteristics and media grain pitch for four quad ECL structures with different G0 thicknesses. These measure magnetic characteristics include: the coercivity, Hc, (FIG. 8); the nucleation field, Hn, (FIG. 9); the switching field distribution, SFD (FIG. 10); the thermal stability factor, KuV/kBT, (FIG. 11); and the intrinsic switching field distribution, iSFD, (FIG. 12). As discussed previously, to achieve an areal recording density of at least 1 Tbit/in2, a grain pitch of about 8 nm or less is needed. However, decreasing grain pitch may also result in degrading the aforementioned magnetic characteristics, e.g., Hcdecreases, Hnincreases, SFD increases, KuV/kBT decreases, and iSFD increases. Despite the negative effects associated with decreasing grain pitch, increasing the thickness of the G0 layer to be in a range from about 6 nm to about 7.4 nm when the grain pitch is about 8 nm or less nonetheless yields desired values for Hc, Hn, SFD, KuV/kBT, and iSFD, as shown inFIGS. 8-12.

FIG. 13provides a plot illustrating the relationship between magnetic cluster size and media grain pitch for four quad ECL structures with different G0 thicknesses. One having skill in the art would not necessarily expect the magnetic cluster size, corresponding to the reversal unit of magnetization in the granular magnetic recording layer, to continually decrease with decreasing grain size and pitch. For instance, a plot of magnetic cluster size versus grain pitch for a triple ECL structure typically exhibits a “cluster size knee” characteristic of a cluster size that initially decreases with grain pitch until a particular grain pitch is reached, after which the cluster size increases as the grain pitch continues to decrease. However, it has been surprisingly and unexpectedly found that for quad ECL structures having a G0 layer with a thickness in a range from about 6 nm to about 7.4 nm, the magnetic cluster size continually decreases with decreasing grain pitch and thus does not exhibit a cluster size knee.

FIG. 14shows a plot illustrating the relationship between overwrite (OW) and media grain pitch for four quad ECL structures with different G0 thicknesses and a triple ECL structure. As shown inFIG. 14, the OW does not significantly vary with grain size and pitch; however, the OW does strongly depend on G0 thickness. Moreover,FIG. 14highlights the surprising and unexpected results that quad ECL structures having a G0 layer with a thickness in a range from about 6 nm to about 7.4 nm exhibit comparable or superior OW results compared to the triple ECL structure having a G1 layer with a thickness of about 5 nm.

FIG. 15shows a plot illustrating the relationship between magnetic core width (MCW) and media grain pitch for four quad ECL structures with different G0 thicknesses and a triple ECL structure. In particular,FIG. 15provides a plot of the 6TMCW versus grain pitch. Frequency T (or 1T) is the highest linear frequency for a particular PMR medium. For example, if 1T=1460 kfci, 2T indicates that the frequency is half of the 1T frequency (i.e., 2T=730 kfci), and 6T would be ⅙ of the 1T frequency (e.g., 6T=about 243 kfci). Accordingly, 6TMCW is the magnetic core width at frequency T/6.

As shown inFIG. 15, while the 6TMCW does not significantly vary with grain size, it does strongly depend on G0 thickness.FIG. 15further highlights that quad ECL structures having a G0 layer with a thickness in a range from about 6 nm to about 7.4 nm exhibit a comparable or superior 6TMCW compared to the triple ECL structure having a G1 layer with a thickness of about 5 nm.

FIGS. 16-18show several plots illustrating the relationship between SoNR and media grain pitch for four quad ECL structures with different G0 thicknesses and a triple ECL structure. In particular,FIG. 16provides a plot of 6TSoNR versus grain pitch;FIG. 17provides a plot of 2TSoNR versus grain pitch; andFIG. 18provides a plot of 1TSoNR versus grain pitch. SoNR refers to the spectral signal-to-noise ratio at a fixed signal measured at a fixed linear density. Stated another way, SoNR refers to the low frequency signal (So) [measured at about 100 kfci (kiloflux changes per inch)] over the integrated noise power at a frequency of T. As noted above, frequency T (or 1T) is the highest linear frequency for a particular PMR medium. Accordingly, 1TSNR is the spectral signal-to-noise ratio of the signal (S) (at a frequency T) over the integrated noise power at a frequency of T; 2TSNR is the spectral signal-to-noise ratio of the signal (S) (at a frequency T/2) over the integrated noise power at a frequency of T/2; and 6TSNR is the spectral signal-to-noise ratio of the signal (S) (at a frequency T/6) over the integrated noise power at a frequency of T/6.

SoNR measurements differ from SNR measurements only in that the signal used for the SoNR corresponds to the low frequency signal, So. SoNR measurements provide a better sense of how the noise alone increases with increasing frequency, whereas SNR measurements combines the signal rolloff (signal decreases with increasing frequency) and the integrated noise increase with increasing linear frequency.

As shown inFIGS. 16-17, there is no significant variation in the 6TSoNR and 2TSoNR for different grain pitch values; however, a dependence between the G0 thickness and the 6TSoNR, 2TSoNR is evident. In particular,FIGS. 16-17highlight that quad ECL structures having a G0 layer with a thickness preferably in a range from about 6 nm to about 7 nm exhibit a comparable or superior 6TSoNR and 2TSoNR compared to the triple ECL structure having a G1 layer with a thickness of about 5 nm.

FIG. 18illustrates that the SoNR at the highest linear density (1TSoNR) does vary with grain pitch to a greater extent than the 6T SoNR and 2T SoNR. Similar toFIGS. 16-17,FIG. 18also illustrates a dependence between G0 thickness and 1TSoNR, where quad ECL structures having a G0 layer with a thickness preferably in a range from about 6 nm to about 7 nm exhibit a comparable or superior 1TSoNR compared to the triple ECL structure having a G1 layer with a thickness of about 5 nm.

FIGS. 19-20show several plots illustrating the relationship between SoNR and MCW for four quad ECL structures with different G0 thicknesses and a triple ECL structure. In particular,FIG. 19provides a plot of 2TSoNR versus 6TMCW, andFIG. 20provides a plot of 1TSoNR versus 6TMCW.FIGS. 19 and 20highlight the dependence between MCW and G0 thickness, as well as the comparable and superior 1TSoNR and 2TSoNR values for quad ECL structures having a G0 layer with a thickness preferably in a range from about 6 nm to about 7 nm as compared to the triple ECL structure having a G1 layer with a thickness of about 5 nm.

FIGS. 21-22show several plots illustrating the relationship between SoNR and MCW for a quad ECL structure compared to two triple ECL structures. Specifically,FIG. 21provides a plot of 2TSoNR versus 6TMCW, andFIG. 22provides a plot of 1TSoNR versus 6TMCW. Moreover, forFIGS. 21-22, the quad ECL structure (corresponding to the circular indicators) has a media grain pitch of 8.1 nm and a 6.3 nm thick G0 layer; the triple ECL structure (corresponding to the square indicator) has a media grain pitch of 8.7 nm and a 5.3 nm thick G1 layer; and the triple ECL structure (corresponding to the triangular indicator) has a media grain pitch of 8.8 nm and a 5.1 nm thick G1.

FIG. 23shows a plot illustrating the relationship between OW and G0 thickness for three quad ECL structures with different EBL structure thicknesses and a triple ECL structure. The EBL structure thicknesses for each ECL structure shown inFIG. 23is as follows:

As shown inFIG. 23, each of the quad ECL structures having G0 thicknesses up to about 6.5 nm exhibit superior results in writeability as compared to the triple ECL structure. However, it is of note that the writeability advantage for the quad ECL structure corresponding to the circular indicators may begin to decrease for G0 thicknesses greater than about 6.5 nm due to the greater overall thickness of the quad ECL structure. Accordingly, as also shown inFIG. 23, reducing the thickness of the EBL structure in the quad ECL structures further improves writeability.

FIGS. 24-27show plots illustrating the relationship between various measured magnetic characteristics and overall thickness of the SUL structure for two quad ECL structures and a triple ECL structure. These measure magnetic characteristics include: OW (FIG. 24); MCW (FIG. 25); 2TSoNR (FIG. 26); and 1TSoNR (FIG. 27). The two quad ECL structures shown inFIGS. 24-27have a G0 thickness of about 6.3 nm, whereas the triple ECL structure has a G1 thickness of about 5.3 nm. Additionally, the two quad ECL structures have different cap layer compositions that differ primarily with regard to the amount of O2flowing during the sputtering deposition. Particularly, the quad ECL structure represented by the square indicators inFIGS. 24-27has a cap layer with a higher moment than the quad ECL structure represented by the circular indicators.

Review ofFIGS. 24-27reveals that the quad ECL structures having a SUL structure with a thickness in a range from about 12 nm to about 25 nm exhibit comparable or superior OW results compared to the triple ECL that has a 30 nm thick SUL structure. Moreover, the quad ECL structures having a SUL structure with a thickness in a range from about 12 nm to about 25 nm exhibit a comparable or narrower MCW while still maintaining good SoNR.

Referring now to Table 1 below, several measurements of recording characteristics are shown for a triple ECL structure and three quad ECL structures. Each of the quad ECL structures (A-C) have a 6.3 nm thick G0 layer; whereas the triple ECL structure has a 5.3 nm thick G1 layer. Moreover, the primary difference between the three quad ECL structures (A-C) corresponds to the degree of lateral exchange coupling in the cap layer, with quad ECL B having a cap layer with a greater degree of lateral exchange coupling than quad ECL A, and quad ECL C having the greatest degree of lateral exchange coupling as compared to quad ECL A and quad ECL B.

It is evident from Table 1, that the quad ECL structures exhibit comparable or superior recording characteristics as compared to the triple ECL structure. For example, a comparison between the quad ECL structure A and the triple ECL structure reveals that the quad ECL structure A exhibits about 0.1 order N-SER gain, about the same OW, a narrower MCW and greater than about 1% ADC_FOM gain.

It should also be noted that methodology presented herein for at least some of the various embodiments may be implemented, in whole or in part, in computer hardware, software, by hand, using specialty equipment, etc. and combinations thereof.

Moreover, any of the structures and/or steps may be implemented using known materials and/or techniques, as would become apparent to one skilled in the art upon reading the present specification.