Damping control in magnetic nano-elements using ultrathin damping layer

A write head and a method for forming the write head. The method includes providing a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. Regions of the write head including at least a portion of at least one of the first pole and the second pole of the write head are volumetrically doped with a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal. The dopant material is predetermined to provide a magnetic damping in the doped regions which is greater than the magnetic damping in the ferromagnetic material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to magnetic materials. Specifically, embodiments of the invention relate to magnetic films and nanostructures, methods for manufacturing magnetic films and nanostructures, and apparatuses using magnetic films and nanostructures.

2. Description of the Related Art

Many modern electronic memory devices such as random access memories (RAM) and hard disk drives are used to store and retrieve data. In some cases, such memory devices may incorporate ferromagnetic materials which may be subjected to an externally applied magnetic field which may switch their magnetization between two stable orientations representing, for example, two logical values. Typically, when a magnetic field applied to a ferromagnetic material is switched from a first value to a second value, the magnetization of the ferromagnetic material may not immediately switch from the first value to the second value. For example, the magnetization of the ferromagnetic material may be subject to magnetic precession wherein the magnetization of the ferromagnetic material oscillates (or “rings”) until settling at a steady state value.

In some cases, magnetic precession of the magnetization of a ferromagnetic material may be affected by intrinsic properties of the material. The amount of time needed for the magnetization within a material to reach a steady state after the magnetic field applied to the material has been switched is described by the so-called Gilbert magnetic damping coefficient (α) for the material. If the magnetic damping coefficient is high, then the magnetization of the material may reach a steady state value more quickly after the applied magnetic field has switched than for materials with a lower magnetic damping coefficient, resulting in a sharper transition of the magnetization of the ferromagnetic material to the steady state value.

In some cases, a high magnetic damping coefficient for a ferromagnetic material may be desired, for example in magnetic data storage applications, where a sharp transition of the magnetization of the ferromagnetic material under switching conditions may be desired, for example, to achieve high data transfer rates and storage densities. Accordingly, what is needed is an improved material having a high magnetic damping coefficient, a method for making the material, and apparatuses incorporating the material.

SUMMARY OF THE INVENTION

One embodiment of the invention provides a method for forming a write head. The method includes providing a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. The method also includes volumetrically doping regions of the write head including at least a portion of at least one of the first pole and the second pole of the write head with a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal. The dopant material is predetermined to provide a magnetic damping in the doped regions which is greater than the magnetic damping in the ferromagnetic material.

One embodiment of the invention also provides a magnetic write head. The magnetic write head includes a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. At least one of the first pole and the second pole are doped a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal. The dopant material is predetermined to provide a magnetic damping which is greater than the magnetic damping in the ferromagnetic material.

One embodiment of the invention also provides a hard drive. The hard drive includes a magnetic storage medium and a magnetic write head configured to write to the magnetic storage medium. The write head comprises a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. At least one of the first pole and the second pole are doped a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal. The dopant material is predetermined to provide a magnetic damping n doped regions which is greater than the magnetic damping in the ferromagnetic material.

Another embodiment of the invention provides a method for forming a write head. The method includes providing a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. The method also includes volumetrically doping regions of the write head including at least a portion of at least one of the first pole and the second pole of the write head with a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal excluding Gadolinium.

One embodiment of the invention further provides a write head. The write head includes a first pole and a second pole. The first pole and the second pole are formed from a ferromagnetic material. The write head comprises doped regions of the ferromagnetic material wherein at least a portion of at least one of the first pole and the second pole of the write head include a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal excluding Gadolinium.

DETAILED DESCRIPTION

Embodiments of the present invention provide a thin-film ferromagnetic layer system which may be used in a variety of electronic devices. In one embodiment, the layer system includes a bilayer with a first layer of ferromagnetic material doped with a dopant selected from one of a 4f rare earth metal, 4d transition metal, and 5d transition metal, wherein the dopant is predetermined to produce an increased magnetic damping within the bilayer. The bilayer also includes a second layer of ferromagnetic material disposed on the first layer. By disposing the second layer on the first layer, the first layer and second layer may be exchange coupled, thereby increasing the magnetic damping within the second layer. The increased magnetic damping in the bilayer may provide magnetic field transitions in both the first and second layer which reach a steady-state value more quickly, i.e., with shorter-lasting, reduced oscillations or ringing than undoped ferromagnetic materials. Furthermore, harmful contact between the first layer and a surface of the second layer may be prevented in a bilayer. For example, any activity at the interface between the second layer and further material may be protected from disturbances other than damping which are caused by the presence of the dopant material. In some cases, interface activities that are necessary for the operation of the device may be highly affected by the choice of materials at the surface of the second layer. The second layer may isolate the first layer from any activity to which the surface of the second layer may be exposed, thereby preventing degradation of the first layer. Optionally, the second layer may prevent exposure of the first layer to an atmosphere containing oxygen, or exposure of the first layer to a warm, humid atmosphere, thereby preventing detrimental oxidation or corrosion of the first layer.

Embodiments of the invention also provide a write head and a method for forming a write head. The method includes providing a first pole and a second pole for the write head. The first pole and the second pole are formed from a ferromagnetic material. The method also includes volumetrically doping regions of the write head including at least a portion of at least one of the first pole and the second pole of the write head with a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal. The dopant material is predetermined to provide a magnetic damping in the doped regions which is greater than the magnetic damping in the ferromagnetic material.

FIG. 1is a block diagram depicting an exemplary bilayer100according to one embodiment of the invention. As depicted, the bilayer may include a first layer102and a second layer104. In one embodiment, the first layer102may be formed of a ferromagnetic material and an additional dopant material. For example, the first layer102may be formed from cobalt-iron and a dopant material (e.g., CoFeX, where X is the dopant material). The ferromagnetic material in the first layer102may also include nickel-iron (NiFe) or any other ferromagnetic material. Similarly, the second layer may be formed from a ferromagnetic material such as CoFe, NiFe, or any other appropriate ferromagnetic material. In one embodiment, the first layer102and the second layer104may be formed from the same ferromagnetic material. Optionally, the first layer102and the second layer104may be formed from different ferromagnetic materials. For example, the first layer102may be formed from NiFe and a dopant material while the second layer104may be formed from CoFe.

In one embodiment, the dopant material may include one of a 4d or 5d transition metal. The 4d transition metals may include niobium (Nb), ruthenium (Ru), and rhodium (Rh). 5d transition metals may include tantalum (Ta), osmium (Os), and platinum (Pt). In one embodiment, the dopant material may also be a 4f rare earth metal. The 4f rare earth metals may include the 14 lanthanides with a partially or completely filled 4f electron shell: cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

In one embodiment of the invention, the selected dopant material may be predetermined to provide increased magnetic damping within the first layer102. Thus, in one embodiment, some elements listed above, such as the 4f rare earth metals europium and gadolinium, which may not produce increased damping in the first layer, may not be used as a dopant in the first layer102. In some cases, the increased magnetic damping may be described in terms of decay time of a magnetic signal, described below in greater detail. For example, the increased magnetic damping may be expressed as a magnetic damping which provides a decay time which is smaller than the intrinsic decay time of the ferromagnetic material used in the first layer102. For example, if the intrinsic decay time of the first layer before doping is 0.65 nanoseconds (ns), then the selected dopant may provide a decay time which is less than 0.65 ns in the doped first layer102.

Furthermore, while embodiments of the invention include a first layer102which includes any amount of a selected dopant material described above, in one embodiment of the invention, the amount of dopant in the first layer102may not exceed an amount which provides sufficient magnetic damping in the first layer102. For example, in one embodiment, the dopant material may be less than or equal to fifteen percent (15%) of the first layer102.

FIG. 2is a flow diagram depicting a process200for forming the magnetic bilayer100according to one embodiment of the invention. In one embodiment, the process200may include providing a substrate material at step202. The substrate material may provide a base on which other layers, including the bilayer100, may be placed, e.g., via deposition, growth, or any other method known to those skilled in the art. At step204, a doped ferromagnetic material layer (e.g., the first layer102) disposed above the substrate may be provided. The dopant material, as described above, may include one of the 4d transition metals, 5d transition metals, and 4f rare earth metals. In one embodiment of the invention, the doping of the ferromagnetic material within the first layer102may be performed via co-deposition (e.g., by sputtering) of the ferromagnetic material and the dopant material. Optionally, any other appropriate method of doping known to those skilled in the art may be used to provide the dopant material and ferromagnetic material within the first layer102.

At step206, an un-doped ferromagnetic material layer (e.g., the second layer104) disposed on the doped ferromagnetic material layer (the first layer102) may be provided. In one embodiment, by providing the second layer104disposed on the first layer102(or vice versa), the first layer102and the second layer104may experience exchange coupling wherein the magnetizations within the first layer102and second layer104are coupled to each other (e.g., a change in the magnetization in the first layer102may cause a similar change in the magnetic field in the second layer104). Thus, the magnetic damping provided by the dopant material in the first layer102may also extend to the second layer104.

In one embodiment of the invention, the magnetic damping in the second layer104may be controlled (and, for example, specifically increased) by the increased damping in the first layer102via direct or indirect exchange coupling of the two magnetic layers102,104. Control of the exchange coupling may, for example, allow independent control of the damping and other magnetic properties such as, for example, magnetization and spin polarization of the second layer104. Such control may allow improved device performance in a number of magnetic data storage-related applications described herein.

In one embodiment of the invention, the exchange coupling at the interface between the first layer102and second layer104, measured by the surface exchange energy density Js in ergs per square centimeter (erg/cm2) may be between 0 and 3 erg/cm2, where the case of Js=0 describes purely magnetostatic coupling between the layers. Similarly, the damping in the first layer102may be between 0.01 and 0.15, as observed in macroscopic measurements of undoped and doped Permalloy, and similarly the damping in the second layer104may be between 0.01 and 0.05 as observed in undoped soft magnetic materials. However, in some cases, determination of atomistic damping in magnetic materials may be difficult in some cases only effective damping at the macroscopic level may be measured. Accordingly, embodiments of the invention may also cover all material combinations of the first layer and second layer where the damping coefficient α1 of the first layer102is significantly larger than the damping coefficient α2 of the second layer104.

In some cases, the coupling between the first layer102and the second layer104may decrease with distance from the point where the first layer102and the second layer104contact each other (referred to as the interface between the first layer102and the second layer104). Thus, in some cases, the magnetic damping provided by the first layer102to the second layer104may decrease with distance from the interface between the first layer102and the second layer104.

As depicted inFIG. 1, the first layer102may have a first thickness T1and the second layer104may have a second thickness T2. As described above, in some cases, magnetic damping provided by exchange coupling between the first layer102and second layer104may decrease in the second layer104with distance from the interface between the first layer102and the second layer104. While embodiments of the invention cover any thickness T2of the second layer104, in one embodiment of the invention, the thickness of the second layer may also be below a selected thickness. Such an upper limit on thickness may, in some cases, provide sufficient magnetic damping throughout the second layer104without a significant decrease in magnetic damping within the second layer. For example, in one embodiment of the invention, the thickness of the second layer may be less than or equal to twenty nanometers (T2<=20 nm). As described below, where layers with a greater magnetic damping and a greater thickness are desired, multiple bilayers100may be laminated (e.g., multiple alternated first and second layers may be deposited) to provide the increased magnetic damping across the increased thickness of the laminated bilayers.

In some cases, in order to avoid over-damping, reduction of the exchange coupling between the first and second layers102,104may also be desired. In one embodiment of the invention, additional layers sandwiched between the first layer102and the second layer104may provide reduced exchange coupling. For example, the first layer102and second layer104may be formed as part of a trilayer which includes a third layer located in between the first layer102and the second layer104. The third layer may include a non-magnetic spacer layer which reduces the exchange coupling between the first and second layer102,104. In one embodiment of the invention, the third layer may be formed from copper (Cu) or ruthenium (Ru).

In one embodiment of the invention, the thickness of the second layer104may be selected to provide isolation for the first layer102from a material or location to which the second layer104may be exposed (e.g., isolation from/to a critical interface within a device, described below, or an atmosphere containing oxygen, both of which may be detrimental to the first layer102) as described above. For example, in one embodiment of the invention, the first layer may be greater than or equal to 2 nanometers (nm) thick (T2>=2 nm).

As mentioned above, in one embodiment of the invention, the first layer102may not be placed at a critical interface within a device. A critical interface may include any interface within a device where an activity takes place which is necessary for operation of the device. Embodiments of the invention may provide increased magnetic damping of the functional first layer102without placing the first layer102directly at a critical interface. For example, in a tunneling sensor, the first layer102may not be placed adjacent to the tunneling layer where the tunneling effect within the sensor occurs. Similarly, in a giant magneto-resistive-type sensor (GMR sensor) or anisotropic magnetoresistive-type sensor (AMR sensor), the first layer102may not be placed adjacent to the separation layer between the free layer and pinned layer. In some cases, presence of dopants like the rare earth metal at the critical interface may have strong detrimental effects on the spin transport and thus the performance-critical magneto-resistance of the device. As described above, the bilayer may prevent such interference while still providing increased magnetic damping by placing the second layer104between the doped first layer102and the critical interface.

While embodiments of the invention may cover a first layer102with any thickness T1, in one embodiment of the invention, the thickness T1of the first layer102may not exceed a selected thickness. In one embodiment of the invention, the doped first layer102may be under eight nanometers thick (e.g., the first layer102may be 5 nm thick). Optionally, where desired, the thickness of the first layer102may be less than or equal to two nanometers (T1<=2 nm). Such a thickness may provide sufficient magnetic damping in the first and second layers102,104while minimizing the overhead devoted to forming the first layer102and, as described above, reducing exposure of the doped first layer102to detrimental conditions.

FIGS. 3A-Dare block diagrams depicting results of micromagnetic simulations of exemplary properties of a bilayer nano-element according to one embodiment of the invention. As depicted inFIG. 3A, decay time for a fluctuating magnetization (e.g., resulting from a change in an applied external magnetic field), which may be inversely proportional to magnetic damping, may be strong throughout the first layer102and may decrease in the second layer104with distance from the interface between the first and second layers102,104.

For the embodiment depicted inFIG. 3A, the exchange coupling is relatively small with an exchange constant in the undoped second layer104of 2.3e-11 J/m in the second layer104. By increasing the exchange coupling between the layers102,104, the magnetic damping may not decrease as quickly with respect to distance from the interface between the layers102,104. For example, as depicted inFIG. 3B, with an exchange constant of 3.0e-11 J/m in the undoped second layer104, the magnetic damping in the second layer104may not decrease significantly at a distance of fourteen nanometers from the interface between the first and second layers102,104.

As depicted inFIG. 3C, according to one embodiment of the invention, the decay time in the doped first layer102may increase with the thickness T1of the first layer102. However, even with a thickness of one nanometer, the decay time in the first layer102may be reduced by more than sixty percent (e.g., from 3.76 nanoseconds (ns) to 1.5 ns).FIG. 3Ddepicts the inverse relationship between decay time and magnetic damping in a doped ferromagnetic layer with uniform magnetic damping according to one embodiment of the invention. By comparingFIGS. 3B,3C, and3D, it is apparent that a doped first layer102of one nanometer thickness and a magnetic damping coefficient of 0.17 is as effective in damping an undoped second layer104which is fourteen nanometers thick (as inFIG. 3B) as uniform doping of an entire ferromagnetic layer fifteen nanometers thick with a uniform damping coefficient of 0.03. Thus, by increasing the magnetic damping in the first layer102, damping in the second layer104may also be increased without any doping of the second layer104.

Use of the Layer System in Devices

In one embodiment of the invention, the layer system, e.g. the bilayer100may be used in one or more electronic devices. Such devices may include a hard drive, magnetic random access memory (MRAM), and spin-torque memory device. Embodiments also provide nanostructures such as nano-wires or nano-particles made of the material of the second layer104covered by material of the first layer102or vice versa.

Within a hard drive, the bilayer100may be used within a magnetic read/write sensor or within the hard disk. The read/write sensor may include any type of read sensor known to those skilled in the art such as a tunneling magneto-resistive (TMR) sensor, a giant magneto-resistive (GMR) sensor, or an Anisotropic Magnetoresistive (AMR) sensor. Such read sensors may also be top-spin, bottom-spin, or dual-spin type read sensors. The bilayer100may also be used in the magnetic write pole of a read/write sensor or in the magnetic shields of a read/write sensor.

FIG. 4is a block diagram depicting a hard drive400according to one embodiment of the invention. The hard disk drive400includes a magnetic media hard disk412mounted upon a motorized spindle414. An actuator arm416is pivotally mounted within the hard disk drive400with a slider420disposed upon a distal end422of the actuator arm416. During operation of the hard disk drive400, the hard disk412rotates upon the spindle414and the slider420acts as an air bearing surface (ABS) adapted for flying above the surface of the disk412. The slider420includes a substrate base upon which various layers and structures that form a magnetic read/write sensor are fabricated. Magnetic read/write heads disclosed herein can be fabricated in large quantities upon a substrate and subsequently sliced into discrete magnetic read/write sensors for use in devices such as the hard disk drive400.

FIG. 5Ais a block diagram depicting the read/write head500within the hard drive400according to one embodiment of the invention. The write head500depicted inFIG. 5Amay be referred to as a perpendicular write head. In general, embodiments of the invention may be utilized with any type of read/write head500, including the perpendicular pole type of write head500depicted inFIG. 5A. Components of the read/write head500may be formed on a substrate520. The read/write head may include a thin-film read sensor514which may be used to read data from the disk412via an upper electrode512and a lower electrode516. An upper magnetic shield510and a lower magnetic shield518, as well as an insulating layer508may be provided to shield the read sensor514from magnetic or electrical interference from other parts of the read/write head500(e.g., from interference caused by the write components in the read/write head500) or from other components within the disk drive400. Aspects of the read sensor514are described below in greater detail with respect toFIG. 6.

The magnetic read/write head500may also include circuitry components configured to write data to the disk412. Such circuitry may include a magnetic coil504configured to induce a magnetic field between a magnetic write pole502and a magnetic return pole506. The induced magnetic field may be used to write data to the disk412, for example, by setting a bit or clearing a bit beneath the write pole502and the return pole506.

In one embodiment of the invention, the magnetic write pole502and/or the magnetic return pole506may be formed from a single bilayer100or laminated bilayers as described below. Alternatively, in one embodiment of the invention, one or more portions of the head500may be formed from a single doped material. In one embodiment of the invention, the dopant material provided for the head500may be predetermined to provide a magnetic damping in the doped areas which is greater than the intrinsic magnetic damping in the ferromagnetic material being doped. For example, the doped material may include a ferromagnetic material such as nickel-iron (NiFe) which is doped with a dopant material selected from one of a 4d transition metal, 5d transition metal, and 4f rare earth metal, excluding Gadolinium. In one embodiment, any composition of the NiFe alloy may be used, including Ni80Fe20 and Ni45Fe55.

In some cases, the doped regions of the head500may be volumetrically doped, such that the doped region is continuous and such that no bilayer100is included in the portions of the head500where the single doped layer is utilized. Doping may be performed using any appropriate method. For example, doping may be performed by co-sputtering, diffusion or implantation techniques, plating, and any other doping techniques known to those skilled in the art. In one embodiment, the head500may also be made from multiple types of ferromagnetic material. For example, portions of the head500may be formed from any combination of NiFe alloys, cobalt-iron (CoFe) alloys, and cobalt-nickel-iron (CoNiFe) alloys. In one embodiment, the pole regions502,506may include one or more of CoFe alloys and CoNiFe alloys, thereby providing improved magnetic polarization for the pole regions502,506.

In one embodiment, when the head500is doped with the dopant material, doping may not be performed on areas of the head500which are exposed to the air-bearing surface530and/or hard disk412. In some cases, where doping is not performed on areas of the head500which are exposed to the air-bearing surface530and/or hard disk412, corrosion of those areas may be prevented. For example, in one embodiment, all ferromagnetic portions of the write head500excluding those exposed to the air-bearing surface530and/or hard disk412may be doped with the dopant material. In an alternative embodiment, the areas of the head500which are exposed to the air-bearing surface530and/or hard disk412may also be doped with the dopant material as described herein. For example, in one embodiment, all ferromagnetic portions of the write head500including those exposed to the air-bearing surface530and/or hard disk412may be doped with the dopant material. In some cases, protective overcoats, including carbon, silicon-nitride (SiN), or other tribologically robust materials may be applied over regions of the head500including, for example, the doped regions.

In one embodiment, the dopant material may form from approximately 0% to 15% of the regions which are doped, thereby providing an increase in damping as described herein. In some cases, areas of the head500which are doped may each be doped uniformly (e.g., with the same concentration of dopants). Optionally, different areas of the head500may be doped with differing concentrations of the dopant material.

While described above with respect to doping regions of a perpendicular pole type write head500, embodiments of the invention may also be utilized with a ring-type write head550as depicted inFIG. 5B. The write head550depicted inFIG. 5Bmay be referred to as a longitudinal write head. The depicted write head550may also be used with the hard drive400described above. As depicted, the write head550may include a first pole560and a second pole570. The first pole560may include a first pole yoke562, first pole pedestal564, and first pole notch566. The second pole570may include a second pole yoke572and a second pole pedestal574. The first pole560and second pole570may be separated by a gap580facing the air-bearing surface552of the write head550. The gap580may be 20 to 100 nanometers wide and may include an air gap or may be filled with a non-magnetic material. The first pole560and second pole570may also be connected by a back gap554.

In one embodiment of the invention, one or more portions of the head550may be formed from a single doped material as described above. For example, in one embodiment, the entire head550may be doped with the dopant material, including the first pole560and the second pole570. In another embodiment, only a single pole (e.g., the first pole560or the second pole570) may be doped with the dopant material. For example, in one embodiment, only the first pole pedestal564and first pole notch566may be doped. Where the second pole570is doped, the doped areas may include only the second pole yoke572and the second pole pedestal574. In another embodiment, only the second pole pedestal574, first pole notch566, and first pole pedestal564may be doped with the dopant material. In another embodiment, only pieces adjacent to the gap580may be doped (e.g., only the first pole pedestal564, second pole pedestal574, and the first pole notch566). In another embodiment, only the first pole notch566and second pole pedestal574may be doped. In a further embodiment, only the back gap554, first pole yoke562, and second pole yoke572may be doped.

In one embodiment, when the head550is doped with the dopant material, doping may not be performed on areas of the head550which are exposed to the air-bearing surface552and/or hard disk412. In some cases, where doping is not performed on areas of the head550which are exposed to the air-bearing surface552and/or hard disk412, corrosion of those areas may be prevented. For example, in one embodiment, all ferromagnetic portions of the write head550excluding those exposed to the air-bearing surface552and/or hard disk412may be doped with the dopant material. In an alternative embodiment, the areas of the head550which are exposed to the air-bearing surface552and/or hard disk412may also be doped with the dopant material as described herein. For example, in one embodiment, all ferromagnetic portions of the write head550including those exposed to the air-bearing surface552and/or hard disk412may be doped with the dopant material.

As described above, the doped regions of the head550may be volumetrically doped, such that the doped region is continuous and such that no bilayer100is included in the portions of the head550where the single doped layer is utilized. Doping may be performed using any appropriate method. For example, doping may be performed by co-sputtering, diffusion or implantation techniques, plating, and any other doping techniques known to those skilled in the art. In one embodiment, the dopant material may form from approximately 0% to 15% of the regions which are doped.

FIG. 6is a block diagram depicting exemplary layers including the read sensor514according to one embodiment of the invention. In the depicted embodiment, a tunneling magnetoresistive (TMR) read sensor is shown in which current I tunneling through a tunneling barrier layer626is affected by the alignment of a magnetic field654in a free layer640(the magnetic field654may be changed, e.g., due a magnetic charge stored on a disk412) and a pinned layer620with a magnetic field652which is pinned to a given alignment by an antiferromagnetic (AFM) pinning layer618. The magnetic read head200may have a bottom side608, top side604, a side602which acts as an air bearing surface (ABS), and a back surface606opposite from the ABS side602. While described with respect to a TMR read sensor, embodiments of the invention may be utilized with any type of read sensor known to those skilled in the art.

As depicted, the magnetic read head600may include the substrate520and an initial underlayer612. A magnetic shield layer614may plated on the underlayer612and a Tantalum (Ta) and/or Ruthenium (Ru) spacer layer616may be deposited on the shield layer518. An Iridium-Manganese-Chromium (IrMnCr) pinning layer618may then be deposited on the Ta/Ru spacer layer616, followed by a Cobalt-Iron (CoFe) pinned layer620. In one embodiment, the pinned layer620may be about 25 angstroms (Å) thick. The pinning layer618may fix the direction of a magnetization652of the pinned layer620substantially in a direction directed from right to left or from left to right. On the pinned layer620, another Ru spacer layer622may be deposited, followed by a Cobalt-Iron-Boron (CoFeB) reference layer624. In one embodiment, the reference layer624may be about 20 Å thick. A Magnesium-Oxide tunneling barrier layer626may be deposited on the reference layer624, followed by a free layer640.

As mentioned above, the free layer640may provide a magnetic field654directed either out of the sensor or into the sensor514. Alignment of the magnetic field654within the free layer640may be changed according to which data is stored in the magnetic disk412. The alignment of the magnetic field654may in turn affect the current I flowing through the read sensor514. By measuring the current I, the data stored in the magnetic disk412may be read. In one embodiment of the invention, the free layer640may be formed from the bilayer100described above. Thus, the free layer640may include the doped first layer102and undoped second layer104. By forming the free layer640from the bilayer100described above, changes in the alignment of the magnetic field654of the free layer640may be more defined (e.g., with less ringing) due to the increased magnetic damping of the bilayer100, thereby providing more defined changes in the current I and allowing improved reading of data from the magnetic disk412.

Furthermore, as mentioned above, in one embodiment of the invention, the undoped ferromagnetic second layer104may be placed between the doped first layer102and the interface with the active tunneling barrier layer626(or, in a GMR or AMR sensor, between the doped first layer102and the interface with the active separation layer between the free layer640and pinned layer620). By placing the undoped ferromagnetic second layer104between the doped first layer102and the interface with the active tunneling barrier layer626, the second layer104may isolate the interface with the active layer from the potentially detrimental effects on the spin transport such as a reduction in magnetic moment density or spin polarization caused by the dopants.

After the free layer640, other spacer layers632,634may be deposited on the free layer640followed by a lead layer636and a second shield layer638which is plated on the lead layer636. In general, the depicted layers are exemplary layers and a read sensor514may, in some cases, contain more layers or fewer layers at different thicknesses as known to those skilled in the art. Similarly, materials other than those shown may be used for given layers as known to those skilled in the art. For example, in one embodiment of the invention, the pinned layer620may be formed from a bilayer100as described above.

In one embodiment of the invention, the upper and/or lower magnetic shields510,518may be formed from the bilayer100. For example, in one embodiment, to provide additional magnetic shielding, the upper and/or lower magnetic shields510,518may be formed from laminated bilayers700(e.g., multiple bilayers100deposited on each other) as depicted inFIG. 7. The laminated bilayers700may include doped ferromagnetic layers702,706,710(each corresponding to the first layer102described above) and alternating undoped ferromagnetic layers704,708,712(each corresponding to the second layer104described above). In one embodiment the thicknesses T1, T3, T5, of the doped ferromagnetic layers702,706,710(corresponding to thickness T1inFIG. 1above) may each be the same. Optionally, some or all of the thicknesses T1, T3, T5may be different in order to provide the desired magnetic damping. Similarly, other properties of the doped ferromagnetic layers702,706,710, such as, for example, the doping in each of the layers702,706,710may be the same or different as desired. Furthermore, with respect to the thicknesses T2, T4, T6and properties of the undoped ferromagnetic layers704,708,712, each may be the same or different as desired.

While described above with respect to laminated bilayers700which may be used in upper and/or lower magnetic shields of a read/write sensor, laminated bilayers700may also be used in other portions of the read/write sensor. For example, in one embodiment of the invention, the magnetic write pole502and/or the magnetic return pole506may be formed from a single bilayer100or laminated bilayers700.

In one embodiment of the invention, the bilayer100(or laminated bilayers700) may also be used in a magnetic disk412as depicted, for example, inFIG. 8. As depicted, the disk412may include a patterned substrate806upon which, for a magnetic bit of data, the doped first layer804(corresponding to the first layer102inFIG. 1) is deposited. The undoped second layer802(corresponding to the second layer104inFIG. 1) may then be deposited over the first layer804. In some cases, bits of data in the recording medium of the magnetic disk may be stored closely together to provide increased information storage density for the disk412. For example, each bit may be stored as magnetization in an area of the recording medium. In general, magnetization or changes in magnetization in a bit may inadvertently interfere with (e.g., alter or weaken) the magnetization in adjacent bits. In some cases, as described above, the undoped second layer802may isolate the doped first layer804from a potentially harmful atmosphere (e.g., within the hard drive housing) surrounding the disk412.

In general, embodiments of the invention may also be used with any ordering of doped and undoped layers. For example, in one embodiment, a sandwiched layer may be formed from an undoped layer deposited between two doped layers, thereby providing exchange coupling between the doped layers and the undoped layer at each end of the undoped layer and providing increased magnetic damping throughout the undoped layer. In one embodiment, a trilayer may also be formed from a doped layer sandwiched between two undoped layers. Each undoped layer may be exchange coupled to the doped layer between the undoped layers, thereby providing increased magnetic damping in each of the undoped layers. Embodiments of the invention may also be utilized with alternating laminations of the sandwiched layers described above (e.g., a first sandwiched layer of doped-undoped-doped material followed by a second sandwiched layer of undoped-doped-undoped material) or any combination/ordering thereof.

In one embodiment of the invention, the doped layer and the undoped layer may not be deposited directly on each other. For example, in one embodiment, one or more non-magnetic metal layers may be deposited between the doped layer and the undoped layer. The metals used in the non-magnetic metal may include, for example, Copper (Cu), Ruthenium (Ru), Iridium (Ir), Chromium (Cr), Palladium (Pd), Platinum (Pt), and/or Rhodium (Rh). Where a non-magnetic metal layer is placed between the doped layer and the undoped layer, the exchange coupling between the doped and undoped layer via the modulating layer may be reduced. By reducing the coupling between the doped layer and the undoped layer, the modulating layer may thereby be used to reduce the damping coefficient in the undoped layer where desired. Such a modulating layer(s) may also be utilized with lamination of layers, sandwiched layers, and laminations of sandwiched layers as described above. Embodiments of the invention may also be utilized with any combination or ordering of bilayers, sandwiched layers, and modulating layers. The modulating layers may also be utilized to provide graded doped and undoped layers described below (e.g., to produce a gradient, multiple laminated layers may include modulating layers varying from large thicknesses which provide large modulation to small thickness or omission of the modulating layer entirely).

Embodiments of the invention may also be used to provide graded doped and undoped layers, for example, such that the combination of alternating layers (including sandwiched layers and modulated layers as described above) provides a magnetic damping coefficient which varies across the alternating layers. In general, any gradient may be provided (e.g., a linear gradient from strong magnetic damping to weak or any varying gradient) according to the desired magnetic damping properties.

In one embodiment of the invention, the bilayer100may also be used in a magnetic random access memory (MRAM) device900depicted, for example, inFIG. 9. The MRAM device900may include control circuitry902configured to receive commands from another electronic device such as a processor or memory controller. The MRAM device900may also include input/output circuitry904configured to input or output data in response to access commands received via the control circuitry902. Data in the MRAM device900may be stored in MRAM memory cells arranged in one or more memory arrays906.

FIG. 10is a block diagram depicting an MRAM memory cell1000which may be included in the MRAM device900according to one embodiment of the invention. As depicted, the memory cell1000may be located at the junction between a word line1002and a bit line1014(depicted running into/out of the page). The memory cell1000may include a free layer1004, tunneling barrier layer1006, pinned layer1008, and pinning layer1010.

During reading of the memory cell1000, current I tunneling through the tunneling barrier layer1006may be affected by the alignment of a magnetic field1020in the free layer1004and a pinned layer1008with a magnetic field1022which is pinned to a given alignment by an antiferromagnetic (AFM) pinning layer1010. During writing of data to the memory cell1000, alignment of the magnetic field1020in the free layer1004may be changed, e.g., by applying an appropriate signal to the word line1002and bit line1014. In one embodiment of the invention, the free layer1004may be formed from the bilayer100described above. Thus, the free layer1004may include the doped first layer102and undoped second layer104. By forming the free layer1004from the bilayer100described above, changes in the alignment of the magnetic field1020of the free layer1004may be more defined with less ringing due to the increased magnetic damping of the bilayer100, thereby providing improved reading and writing of data from the memory cell1000.

Furthermore, in one embodiment of the invention, the undoped ferromagnetic second layer104may be placed between the doped first layer102and the interface with the active tunneling barrier layer1006. By placing the undoped ferromagnetic second layer104between the doped first layer102and the interface with the active tunneling barrier layer1006, the second layer104may isolate the interface with the active layer from the potentially detrimental effects on the spin-dependent tunneling probability caused by the dopants.

While described above with respect to MRAM memory cells1000which are included in an MRAM memory device900, embodiments of the invention may be utilized with any MRAM memory cell1000provided in any type of device. In some cases, the memory cell1000may include additional layers known to those skilled in the art. Furthermore, while described above with respect to MRAM and hard disk drives, embodiments of the invention may be used in any type of device, such as, for example, spin-torque memory devices and nanostructures such as nano-wires or nano-particles made of the material of the second layer104covered by material of the first layer102or vice versa. In such devices, the doping may be used to tailor the spin momentum transfer properties.