Multi-layer magnetoresistive shield with transition metal layer

A magnetic shield that is capable of enhancing magnetic reading. In accordance with various embodiments, a magnetic element has a magnetically responsive stack shielded from magnetic flux and biased to a predetermined default magnetization by at least one lateral side shield that has a transition metal layer disposed between first and second ferromagnetic layers.

SUMMARY

Various embodiments of the present invention are generally directed to a magnetic shield that may be capable of protecting a magnetoresistive element from unwanted magnetic flux. In accordance with various embodiments, a magnetic element has a magnetically responsive stack that may be shielded from unwanted magnetic flux and that may be biased to a predetermined default magnetization by at least one lateral side shield that has a transition metal layer disposed between a first and second ferromagnetic layer.

DETAILED DESCRIPTION

The present disclosure generally relates to magnetic shields that may be capable of protecting a magnetoresistive (MR) element from unwanted magnetic flux. An increasing demand for higher data capacity has placed added emphasis on the amount of data written to a data storage media, which consequently results in a reduction in the size of data bits and magnetic shields. With smaller data bits, magnetic flux from nearby data tracks can be inadvertently sensed and cause reader inaccuracy. Likewise, smaller magnetic shields can lead to increased magnetic instability due to a reduced capability to fully protect the MR element from unwanted magnetic flux.

Accordingly, various embodiments of the present invention are generally directed to a magnetoresistive (MR) element that has a magnetically responsive stack that may be shielded from unwanted magnetic flux and that may be biased to a predetermined default magnetization by at least one lateral side shield. The lateral side shield is constructed as a lamination of at least a transition metal layer disposed between a first and second ferromagnetic layer wherein shielding and biasing for the magnetic stack may be concurrently provided. Such a laminated lateral side shield may allow for enhanced MR element operation through the cross-track capability and better magnetic stability.

While a shielded and biased magnetic element may be used in a variety of non-limiting applications,FIG. 1provides a data storage device100that is capable of utilizing a magnetic element according to an embodiment. The device100is provided to show an environment in which various embodiments of the present invention may be practiced. It will be understood, however, that the claimed invention is not so limited.

The device100includes a substantially sealed housing102formed from a base deck104and top cover (not shown). An internally disposed spindle motor108is configured to rotate by one or more storage media110. The media110are accessed by a corresponding array of data transducers that are each supported by a head gimbal assembly (HGA)112. Each HGA112can be supported by a head-stack assembly114(“actuator”) that includes a flexible suspension116, which in turn is supported by a rigid actuator arm118. In an embodiment, the actuator114pivots about a cartridge bearing assembly120through application of current to a voice coil motor (VCM)122.

In this way, controlled operation of the VCM122causes the transducers124of the HGA112to align with tracks (not shown) defined on the media surfaces to store data thereto or retrieve data therefrom. An ability to decrease the width of the tracks while maintaining proper alignment of the transducers124may be accomplished by decreasing the operational width of at least one transducing magnetic element. Thus, the device100may have increased capacity through the incorporation of transducing elements with reduced operational width which corresponds to a finer areal resolution.

An example data transducing portion130of the data storage device100ofFIG. 1is displayed inFIG. 2. The transducing portion130has an actuating assembly132that positions a transducing head134over a magnetic storage media136that is capable of storing programmed bits138. The storage media136is attached to a spindle motor140that rotates during use to produce an air bearing surface (ABS)142on which a slider portion144of the actuating assembly132flies to position a head gimbal assembly (HGA)146, which includes the transducing head134, over a portion of the media136.

The transducing head134may include one or more transducing elements, such as a magnetic writer and magnetically responsive reader, which operate to program and read data from the storage media136, respectively. As a result, controlled motion of the actuating assembly132causes the transducers to align with tracks (not shown) defined on the storage media surfaces to write, read, and rewrite data. However, the reduction in track widths that corresponds with ever decreasing data bit sizes can induce reading inaccuracies when the magnetic flux from an adjacent track is sensed inadvertently. In view of the susceptibility to proximal data bits138, a magnetic element of the transducer has one or more shields that function to absorb unwanted magnetic flux so that only certain data bits138on a predetermined data track are written and read.

An example transducing head150that employs magnetic shields is generally displayed as a cross-sectional block representation inFIG. 3. The head150can have one or more magnetic transducing elements, such as the magnetic reader152and writer154, which can operate individually, or concurrently, to write data to or retrieve data from an adjacent storage media, such as media136ofFIG. 2. Each magnetic element152and154is constructed with multiple magnetic shields and transducing elements that independently define predetermined read and write tracks that each have a predetermined track width156and158that extend along a Z axis going into and out of the page.

As displayed, the magnetic reading element152has a magnetoresistive reader layer160disposed between leading and trailing shields162and164. Meanwhile, the writing element154has a write pole166and a return pole168that create a writing circuit to impart a certain magnetic orientation to the adjacent storage media. The return pole168is separated from the read element152by a gap layer170of non-magnetic material while the write pole166is disposed between a downtrack shield172and an uptrack shield174that maintains separation of the write and return poles166and168.

Additional insulating layers176,178, and180respectively surround the write pole166and MR reader layer160to prevent leakage of magnetic flux within the transducing head150. The various shields and insulating materials about each magnetic element152and154provide similar focusing of magnetic fields, but the shields on the ABS182are configured to focus magnetic fields within the predetermined tracks156and158. That is, the insulating materials176and178focus magnetic fields on the write pole166while the shields162,164,172, and174each may prevent the migration of magnetic fields outside the predetermined tracks156and158.

The shields of the transducing head150can be characterized by their position with respect to the timing of encountering external bits, such as bits138ofFIG. 2. In other words, the shields that encounter the external bits before the transducing elements152and154are “leading” shields while shields that see the bits after the transducing elements are“trailing” shields. Such characterization extends to the difference between “upstream” or “downstream” of the transducing elements in that, depending on the direction of travel for the head150and external bits, the shields can be either leading or trailing and either upstream or downstream.

The transducing head150, and each of the respective layers, has a predetermined thickness measured along a Y axis, and a stripe height186measured along an X axis. While not required or limited, the shields162,164, and172may have respective shapes and dimensions that do not vary along the stripe height186. As such, each shield can be configured to maintain a predetermined thickness throughout the extent of each shield's stripe height.

With the predetermined track width158getting smaller to allow more densely programmed bits on a storage media, more precise definition of the track158is used with a reduced physical head150size, which can consequently correspond to a greater sensitivity to unwanted magnetic fields, particularly from lateral magnetic fields from adjacent data tracks. The reduced head150topography can further introduce magnetic instability through magnetic domain generation and movement near the data track edge due to narrow shield-to-shield spacing.

Accordingly, lateral shields can be constructed to supplement the leading and trailing shields162and164to surround the MR element160and better focus magnetic flux to more precisely define data tracks156and158. Such lateral magnetic shields are generally illustrated as a block representation in the example magnetic element190ofFIG. 4, as shown from the air bearing surface (ABS). The cross-sectional view of the magnetic element190inFIG. 4displays an MR reader portion, which may accompany an MR writer as shown inFIG. 3.

The MR element190has a magnetic stack192that is magnetically responsive and capable of sensing data bits that can be interpreted by a host as various logical states. It has been observed that a magnetic stack192that has dual ferromagnetic free layers194separated by a non-magnetic spacer layer196can provide beneficial data sensing in conjunction with reduced shield-to-shield spacing.

The stack192is coupled to leading and trailing shields198and200that respectively maintain a predetermined uptrack and downtrack resolution of data bits. The magnetically sensitive region of the stack192is decoupled from the magnetically active leading and trailing shields198and200by seed and cap layers202and204that are not required or limited to the configuration shown inFIG. 4. However, the leading and trailing shields198and200may provide cross-track data bit resolution used to reliably read high areal density data recordings. Such cross-track resolution can be enhanced by the addition of laminated side shields206that are laterally adjacent and non-contacting with the stack192. In some embodiments, insulating material is positioned between each side shield206and the leading shield198to prevent any current from traveling through the side shields206instead of the stack192.

In operation, a default magnetization is set to one or both of the free layers194with a biasing structure, such as a hard magnet, that is external to the stack192and that may allow sensed data bits to induce a change in the relative angle between the free layers194that is read as a logical state by a host. With each ferromagnetically free layers194not having a fixed magnetization in the stack192to set a default magnetization, a biasing structure can take the form of a rear mounted permanent magnet that sets the default magnetization from the portion of the stack192opposite the ABS. Such a rear mounted magnet can be associated with the formation of data track edge domain creation that combines with the relatively large demagnetization fields generated by the stack192to provide limited cross-track resolution optimization in high areal density data recordings.

In view of the cross-track resolution issues related to rear mounted biasing structures, the side shields198may provide both biasing and shielding operation that concurrently sets a predetermined default magnetization in the stack192and enhances cross-track data bit resolution by absorbing unwanted magnetic flux. Each of the side shields206inFIG. 4have a spacer layer208disposed between a free ferromagnetic layer210that is sensitive to encountered magnetic flux and a pinned ferromagnetic layer212that is set to a predetermined magnetization that is not sensitive to external magnetic flux due to being set to predetermined pinning magnetization.

The presence of both free and pinned magnetizations in each side shield206may allow for the shielding of magnetic flux distal to the magnetic stack192while providing a biasing magnetization that aids in setting a predetermined default magnetization in the stack192. The shielding and biasing characteristics of the side shields206can be adjusted by aligning each layer of the side shield206with the layers of the stack192, which can be facilitated by adding seed and cap layers214and216of particular thicknesses to opposite sides of the side shields206. The aligned magnetizations of the side shields206and magnetic stack192can allow for stronger biasing of the stack192due to increased antiferromagnetic coupling that can be further tuned by adjusting the lateral distance between the side shield206and stack192.

It should be noted that the shielding and biasing features of the side shields206can be modified and tuned in a number of different manners, none of which are required or limited to further enhance the cross-track resolution of the MR element190. One such modification to the configuration of the side shields206is presented in the MR element220ofFIG. 5A. The element220has a magnetic reader stack222with laterally adjacent and non-contacting side shields224that are each constructed with a transition metal layer226disposed between the free and pinned ferromagnetic layers228and230.

As shown in the embodiment ofFIG. 5A, the transition metal layers226are each Ruthenium (Ru) and each pinned and free layer228and230is CoFe. However, the material of the transition metal layers are not limited to the various embodiments shown inFIG. 5A. That is, any number of elements, compounds, and alloys can be used with either insulating or conductive and with or without Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling. For example, the transition metal layers226can individually or collectively be insulating compounds such as, but limited to, AlO and SiO2, or metallic materials with no RKKY interactions, such as Ta, TaN, Ti, and TiN, between the pinned and free layer228and230.

A predetermined magnetization direction is maintained in the pinned layers230by directly coupling an antiferromagnetic (AFM) layer232to each soft magnetic pinned layer230opposite the transition metal layer226. These configurations, however, are not required or limited as a variety of transition metals, such as Ir, Rh, and Cu, and non-magnetic materials, such as MgO, can be used as the transition metal layer226of one or both side shields224. Meanwhile, the free228, pinned230, and metal226layers can be characterized as a synthetic antiferromagnetic (SAF) structure that is comprised of various materials and thicknesses to provide both biasing and shielding for the magnetic stack222in an embodiment.

With side shields224laterally bookending the magnetic stack222, the demagnetization energy of the dual free layers234of the stack222is minimized, which may result in a reduction or elimination of magnetic domain formation in the free layers234and an increased element220read back signal. The enhanced shielding of the side shields224may allow the free layers234of the magnetic stack222to be closer together due to a thinner tunnel junction layer236being disposed therebetween. Furthermore, the strength of the side shields224may allow for a reduction in the width of the shields224, as measured along the Z axis, which can further lead to optimized read back capability in high linear and areal density data bit recordings due to a condensed element220width.

Configuring the side shields224as a SAF structure also may allow for optimized biasing of the stack222free layers234through the induction of substantially orthogonal magnetizations. That is, the biasing fields emitted from each side shield224may induce the free layers234to predetermined default magnetizations that are substantially orthogonal, which enhances reader accuracy and sensing speed. The biasing fields of the side shields224can be further aligned with the layers of the stack222with the inclusion of a seed layer238that may efficiently position the biasing fields of each shield224to induce such substantially orthogonal magnetizations in the stack222.

The biasing of the magnetic stack222can be further aided by a rear magnet that is positioned on the opposite side of the stack222from the ABS, as shown in the isometric view ofFIG. 5B. The magnetic element220shown inFIG. 5Bis constructed with the magnetic stack222laterally flanked by laminated side shields224and positioned between the ABS and a rear bias magnet240. By surrounding the magnetic stack222with biasing structures, the size and biasing strength output of each structure may be reduced, which optimizes the form factor of the element220. The combination of the side shields224and rear bias magnet240further allows the side shields224to provide enhanced cross-track resolution with minimal biasing field specifications.

The construction of a rear bias magnet240in combination with the laminated side shields224also helps ensure the substantially orthogonal magnetization relationship between the stack free layers234. While the rear bias magnet can be constructed as solid ferromagnet or as a lamination of magnetic layers, neither of which are required or limited, the effect of the biasing magnetization on the stack free layers234may reduce the generation of magnetic domains on the ABS due to the lowered magnetic biasing field specifications from the side shields224.

In another example configuration of the side shields,FIG. 6generally illustrates a portion of a magnetic element250that has a magnetic stack252disposed laterally between side shields254each constructed as a lamination of alternating transition metal layers256and soft magnetic free layers258. The alternating lamination of the side shields254provides shielding for the magnetic stack252. The free layers antiferromagnetically couple due to the exchange coupling between the soft magnetic free layers258and the transition metal layers256that can be adjusted to cater to a multitude of predetermined magnetic stack252operating parameters.

With higher data bit recording densities, the ability to precisely tune the shielding efficiency of side shields254may allow for smaller physical magnetic stack sizes that operate with reliability and accuracy. The tunable nature of the side shields254inFIG. 6lies in the numerous variations of materials and thicknesses of the shield laminations. The example shield laminations254each have a common transition metal (Ru) constructed with a common first thickness and disposed between soft magnetic layers such as, but limited to, NiFe and NiCoFe that each has a common second thickness.

However, the shield laminations254ofFIG. 6are merely one embodiment which is not required or limited. As such, other embodiments can have varying transition metal materials and thicknesses that modify the exchange coupling of the free layers258and the shielding efficiency of the side shields254. For example, the number of alternating layers and alignment with the magnetic stack252can be adjusted with shield seed layers260to attain predetermined operation.

The shield seed layers260can be configured in relation to seed and cap layers262and264of the magnetic stack252to position the various laminated layers of each shield254out of alignment with the stack free layers266and tunnel junction268. The lack of alignment between the layers of the stack252and side shields254can modify the biasing field strength imparted on the stack252in combination with complete shielding coverage of each lateral surface of the magnetic stack252.

While the lamination of the side shields254can provide enhanced operation and broadened configurability, the practical manufacture of a magnetic element with laminated side shields can pose difficulties. One such difficulty could be the deposition of side shield layers with uniform thicknesses.FIG. 7generally illustrates a magnetic element270constructed to alleviate manufacturing difficulties while enhancing magnetic shielding and biasing.

The magnetic element270has laminated lateral side shields on either side of a magnetic tunnel junction (MTJ)272that are each constructed, in accordance with an example embodiment, with two ferromagnetic layers274of NiFe each with a40Angstrom thickness alternating with a Ru transition metal layer276that has a20Angstrom thickness. As displayed, the ferromagnetic and transition metal layers274and276of the side shield each continuously extends across the width278of the element270.

The continuous configuration of the layers of the side shields allows for the maintenance of predetermined layer thicknesses, such as 20 or 40 Angstroms, near the MTJ272. Such a configuration also allows a ferromagnetic layer274to extend along a substantial portion of the MTJ's sidewall, as measured along the Y axis. While the extension of a ferromagnetic layer274along the MTJ's sidewall may promote efficient magnetic shielding and reliable layer thicknesses with simplistic manufacturing processes, the MTJ272may be buffered from direct contact with the ferro layers274along its sidewall by an insulation layer280.

The addition of the insulation layer280can supplement a dimension of tunability to the magnetic element270. That is, the variation of the thickness and non-magnetic material of the insulation layer280can be modified to accommodate a variety of different shielding and biasing needs. The configuration of the insulation layer280can also be omitted from the top of the MTJ272so that at least one ferromagnetic layer274is in direct contact with the MTJ272. With the additional thickness of the continuous side shield layers to the element270, either leading or trailing shield282or284can have an area of reduced thickness in the form of a side shield feature that can accommodate the additional side shield layer thickness while maintaining a minimal shield-to-shield spacing. The side shield feature, while not limited to a certain shape or size, can be constructed as a notch, taper, and continuously curvilinear sidewall.

However, the deposition of the side shield layers may be optimized to ensure proper biasing and shielding of the MTJ272.FIG. 8graphs example operational characteristics of a magnetic element, such as the element270ofFIG. 7, to illustrate how the side shield layers can be optimized.

In operation, a laminated side shield, such as the shields ofFIGS. 4-6, will have varying exchange coupling energy depending on the side shield design, particularly with regard to the transition metal layer thickness.FIG. 8graphs example variations in exchange coupling energy which forms at least three defined peaks as transition metal layer thickness increases. As a result of the varying exchange coupling energy, construction of a side shield with a transition metal layer thickness that corresponds with exchange coupling energy that is too high, or too low, may reduce the shielding and biasing operation of the side shield.

While any transition metal layer thickness can be used, an optimal exchange coupling thickness region285can be used in various embodiments where the side shields will continuously antiferromagnetically couple to bias and shield the adjacent MTJ. A transition metal layer thickness that is outside the region285can correspond with the generation of magnetic domains due to some portions of the side shields antiferromagnetically coupling while other portions ferromagnetically coupling. Hence, an optimal transition metal thickness region285provides the bounds of transition metal thickness to remain within the predetermined third exchange energy peak.

Constructing the side shields with uniform side shield layers that have a predetermined thickness that correlates with the third antiferromagnetic exchange energy peak can provide enhanced readback head operation. In some embodiments the thickness of the transition metal layer varies along the entire width of the element, but provides enhanced operation when the thinnest portion of the transition metal layer near the MTJ is within the third peak region285.

An example magnetic element fabrication routine290that can produce a magnetic element with an optimized side shield in accordance with various embodiments of the present invention is presented in the flow chart ofFIG. 9. The routine290begins by depositing one or more seed layer(s) in step292that define a predetermined size and configuration of the magnetic element. While the seed layers can be deposited on a pre-deposited leading shield layer, such a shield layer is not required for the seed layers to define a magnetic stack and side shields on either lateral side of the stack. The deposition of the seed layers in step292also defines the distance between the side shields and the stack, which can play a role in the biasing and shielding characteristics of the side shields.

The routine290next determines the side shield design in decision294by evaluating whether an alternating lamination of layers and a synthetic antiferromagnetic (SAF) lamination. As discussed above, either side shield lamination can provide concurrent magnetic stack biasing and shielding with minimal increased shield-to-shield spacing. If an alternating lamination is chosen in decision294, the routine290proceeds to step296to deposit either a transition metal layer or a ferromagnetic layer onto the seed layer(s). Next in step298, the layer not deposited in step296is deposited. It should be noted that the deposition of different layers can be associated with separate mask and etch operations that define each material layer's thickness, shape, and orientation.

After step298, another transition metal and ferromagnetic layer combination can be deposited by looping through steps296and298any number of times. With a number of alternating side shield layers deposited in a selected ratio, such as a two-to-one ferromagnetic to transition layer ratio, the routine290can move forward with the alternating lamination of ferromagnetic and transition metal layers present on the seed layer. However, if in decision294a SAF structure is sought, step300would deposit an antiferromagnetic AFM material layer followed by the deposition of a ferromagnetic layer in step302that contacts and is pinned by the AFM layer.

Subsequently in steps304and306, a transition metal layer and ferromagnetic free layer are deposited on the pinned layer to form a SAF structure with both a set magnetization in the pinned layer and an external magnetic field sensitive free layer that are separated by the transition metal layer. The configuration of a SAF structure on each lateral side of the magnetic stack can, as discusses above, provide reduced spacing between shielding layers, which results in readback capabilities. Although not explicitly stated in routine290, the magnetic stack comprising of dual ferromagnetic free layers separated by a non-magnetic spacer layer can be deposited concurrently, prior to, or subsequent to the deposition of side shield layers in steps296-306. Regardless of the design and configuration of the side shields, once formed the routine290advances to decision308where the inclusion of a rear bias magnet, such as the magnet240ofFIG. 5B, is determined. A decision for a rear bias magnet then proceeds to step310which deposits the bias magnet near the magnetic stack opposite the ABS surface of the stack.

A determination that no rear bias magnet is needed results in an evaluation of the inclusion of a cap layer in decision312. Thus, decision312is determined with or without a rear bias magnet being present in the magnetic element. In yet, in some embodiments, the cap layer can be deposited before forming the rear bias magnet. With respect to the cap layer determination of decision312, a lack of any need for a cap layer leads to the deposition of a trailing shield in step314over some or all of the magnetic stack and side shields. Meanwhile, a desire for a cap layer advances to the deposition of a trailing shield after depositing a cap layer in step316

With the various decisions and possible configurations of the stack, side shields, and rear bias magnet in routine290, it can be appreciated that none of the blocks and decisions are required or limited. As such, the routine290can be adjusted, much like the configurations and materials of the many layers, to accommodate the construction of a magnetic element that operates in a fashion. For example, the thickness of seed layers in step292can vary between the side shields and stack, as generally shown inFIG. 6, which can involve a multitude of seed layer deposition steps in place of the one step shown inFIG. 9.

In another example modification of routine290, the alignment and materials can vary in a particular side shield or in the entire element, which corresponds with numerous additional steps in routine290to form the side shields with the alignment and material configurations. Thus, the routine290is not required or limited as the various decisions and steps can be omitted, changed, and added as desired to construct a magnetic element with side shields that both bias and shield the magnetic stack.

It can be appreciated that the configuration and material characteristics of the laminated magnetic shields described in the present disclosure allows for enhanced magnetic data bit reading through the reduction or elimination of magnetic domains near the magnetic stack. The utilization of multiple ferromagnetic layers separated by a transition metal layer can minimize magnetic stack demagnetization while increasing the magnetoresistive ratio of the stack by biasing the free layers in a substantially orthogonal relationship.

Moreover, the option of utilizing a SAF and alternating side shield lamination allows for high degrees of tunability for a magnetic element that can result in precise element operation. The inclusion of the lateral side shields that function to concurrently bias and shield the magnetic stack acts to reduce the shield-to-shield spacing, which corresponds to greater magnetic element capabilities in the face of ever increasing areal bit densities on recording media.