Magnetoresistive sensor with SAF structure having crystalline layer and amorphous layer

Implementations disclosed herein provide for a magnetoresistive (MR) sensor including a synthetic antiferromagnetic (SAF) structure that is magnetically coupled to a side shield element. The SAF structure includes at least one magnetic amorphous layer that is an alloy of a ferromagnetic material and a refractory material. The amorphous magnetic layer may be in contact with a non-magnetic layer and antiferromagnetically coupled to a layer in contact with an opposite surface of the non-magnetic layer.

BACKGROUND

Generally, magnetic hard disc drives include transducer heads that read and write data encoded in tangible magnetic storage media. Magnetic flux detected from the surface of the magnetic medium causes rotation of a magnetization vector of a sensing layer or layers within a magnetoresistive (MR) sensor within the transducer head, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring the resulting change in voltage across the MR sensor. Related circuitry can convert the measured voltage change information into an appropriate format and manipulate that information to recover the data encoded on the disc.

As improvements in magnetic recording density capabilities are pursued, the dimensions of transducer heads continue to shrink. Typically, transducer heads are formed as a thin film multilayer structure having an MR sensor, among other structures. In some approaches, the thin film multilayer structure includes a synthetic anti-ferromagnet (SAF) to enhance MR sensor stability. However, existing thin film process and structure designs used in forming SAF-based MR sensors present effects that can nevertheless limit MR sensor performance and stability.

SUMMARY

Implementations described and claimed herein provide a synthetic antiferromagnetic (SAF) structure magnetically coupled a side shield element, the SAF structure including at least one amorphous alloy layer that includes a ferromagnetic material and a refractory material.

This Summary is provided to introduce an election of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will be apparent from the following more particular written Detailed Description of various implementations and implementations as further illustrated in the accompanying drawings and defined in the appended claims.

DETAILED DESCRIPTION

Reducing cross-track magnetic interference is one challenge in creating storage devices with higher areal densities. Some magnetoresistive (MR) sensor designs utilize side shields to reduce cross-track magnetic interference; however, side shields can be sensitive to variation in stray magnetic fields. This sensitivity can result in free layer bias variability within the MR sensor, which can consequentially decrease a signal to noise (SNR) ratio of the MR sensor.

To help stabilize side shields, a pinned synthetic antiferromagnetic (SAF) structure can be incorporated into a shield element proximal to a leading or trailing edge of a sensor stack. The SAF structure is magnetically coupled to the side shields and includes at least two ferromagnetic layers antiferromagnetically coupled together across a non-magnetic spacer coupling layer.

In the above-described sensor design, the strength of the antiferromagnetic coupling in the SAF structure plays a major role in stabilization of the SAF structure and in the stabilization of the side shields. When the interface between the spacer coupling layer and the ferromagnetic layers is rough, the strength of the ferromagnetic coupling within the SAF structure is reduced. This contributes to a reduction in side shield stability, and ultimately to an increase in noise of the MR sensor.

Implementations disclosed herein provide for an SAF structure with one or more ferromagnetic coupling layers comprising a magnetic amorphous alloy. The magnetic amorphous alloy contributes to a “smoother” interface between the ferromagnetic layers and the spacer coupling layer. As a result, the MR sensor exhibits increased stability and a reduction in cross-track magnetic interference.

The technology disclosed herein may be used in conjunction with a variety of different types of MR sensors (e.g., anisotropic magnetoresistive (AMR) sensors, tunneling magnetoresistive (TMR) sensors, giant magnetoresistive (GMR) sensors, etc.). Accordingly, the implementations disclosed herein may also be applicable to new MR sensor designs that are based on new physical phenomena such as lateral spin valve (LSV), spin-hall effect (SHE), spin torque oscillation (STO), etc.

FIG. 1illustrates a plan view of an example disk drive assembly100. The example disk drive assembly100includes a slider120on a distal end of an actuator arm110positioned over a media disk108. A rotary voice coil motor that rotates about an actuator axis of rotation106is used to position the slider120on a data track (e.g., a data track140) and a spindle motor that rotates about disk axis of rotation111is used to rotate the media disk108. Referring specifically to View A, the media disk108includes an outer diameter102and an inner diameter104between which are a number of data tracks, such as a data track140, illustrated by circular dotted lines. A flex cable130provides the requisite electrical connection paths for the slider120while allowing pivotal movement of the actuator arm110during operation.

The slider120is a laminated structure with a variety of layers performing a variety of functions. The slider120includes a writer section (not shown) and one or more MR sensors for reading data off of the media disk108. View B illustrates a side of an example MR sensor130that faces an air-bearing surface (ABS) of the media disk108when the disk drive assembly100is in use. Thus, the MR sensor130shown in View B may be rotated by about 180 degrees about (e.g., about a z-axis) when operationally attached to the slider120shown in View A.

The MR sensor130of the slider120includes a sensor stack132that has a plurality of layers (not shown) that perform a plurality of functions. In various implementations, the functionality and number of such layers may vary. However, the sensor stack132includes at least a magnetic layer with a magnetic moment that is free to rotate in response to an applied magnetic field (i.e., a free layer (not shown)). The data bits on the media disk108are magnetized in a direction normal to the plane ofFIG. 1, either into the plane of the figure, or out of the plane of the figure. Thus, when the MR sensor130passes over a data bit, the magnetic moment of the free layer is rotated either into the plane ofFIG. 1or out of the plane ofFIG. 1, changing the electrical resistance of the MR sensor130. The value of the bit being sensed by the MR sensor130(e.g., either 1 or 0) may therefore be determined based on the current flowing through the sensor stack132.

Side shield elements116and118provide a stabilizing bias to the free layer of the sensor stack132. The side shields116and118are positioned adjacent to the sensor stack132in the cross-track (x-direction), and may be made of soft or hard magnetic material.

In the down-track direction (z-direction), the sensor stack132is positioned between shield elements112and114. The shield elements112and114isolate the sensor stack132from electromagnetic interference, primarily z-direction interference, and serve as electrically conductive first and second electrical leads connected to processing electronics (not shown). In one implementation, the shield elements112,114are constructed of a soft magnetic material (e.g., a Ni—Fe alloy). In another implementation, the shield elements112,114have a z-direction thickness that is substantially larger than the length of a single data bit on a rotating magnetic media. Such thickness may be on the order of 1-2 microns (e.g., approximately one micron) along the data track140.

In operation, a bit along a track140on the media disk108consecutively passes under the shield element112, under the sensor stack132, and then under the shield element114. Therefore, the edge of the sensor stack132proximal to the shield element112may be referred to as the “leading edge” of the sensor stack and the edge of the sensor stack132proximal to the shield element114may be referred to as the “trailing edge” of the sensor stack.

InFIG. 1, the leading edge of the sensor stack132is in contact with the shield element112. In other implementations, one or more layers may be interleaved between the sensor stack132and the shield element112.

The trailing edge of the sensor stack is132is adjacent to a synthetic antiferromagnetic (SAF) structure134, which includes a pinned layer124, a reference layer122, and a spacer coupling layer126. The pinned layer124has a magnetic moment that is biased by an adjacent antiferromagnetic (AFM) layer136. The direction of such biasing (indicated by an arrow in the pinned layer124) is in a direction that is substantially antiparallel to the magnetic orientation of the reference layer122. These antiparallel magnetic orientations are due to an antiferromagnetic coupling across the spacer coupling layer126, which may be a layer of ruthenium or other suitable Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling material.

The pinned layer124and the reference layer122may be made of the same or different materials. In one implementation, one or both of the pinned layer124and the reference layer122are magnetic amorphous alloys including a ferromagnetic material (e.g., Co, Fe, CoFe, NiFe, etc.), and a refractory material, such as tantalum (Ta), niobium (Nb), hafnium (Hf), and zirconium (Zr).

For example, the magnetic amorphous alloy may be CoFeX or NiFeX, where X is a refractory material. In one implementation, the magnetic amorphous alloy includes between 0 and about 30% of the refractory material, or enough to ensure that the resulting alloy is amorphous. In one example implementation, the magnetic amorphous alloy is CoFeNb and comprises 10% Nb. The percent of refractory material included in the amorphous magnetic material is a variable value that may depend upon material types utilized as well as process conditions, such as an annealing temperature.

As used herein, “amorphous” refers to a solid that lacks the long-range order characteristic of a crystal. The magnetic amorphous alloy may be deposited as a thin film and remain amorphous during post-deposition processing, such as during a magnetic annealing process. Suitable magnetic amorphous alloys exhibit one or more of the following properties: magnetic softness, relatively low magnetostriction, high magnetic moments, and a mill rate that is substantially the same as the mill rate of one or more other soft magnetic materials (e.g., NiFe, CoFe) used in the MR sensor130. In one implementation, a suitable magnetic amorphous alloy has a magnetostriction coefficient between −1×10−5and 1×10−5. In another implementation, a suitable magnetic amorphous alloy has a magnetic moment that is greater than the magnetic moment of ferromagnetic material included in the magnetic amorphous alloy. For example, the magnetic amorphous alloy may include NiFe combined with other material, and have a total magnetic moment greater than the magnetic moment of NiFe alone.

Using a magnetic amorphous alloy for the pinned layer124and/or the reference layer122instead of a crystalline material allows for a smoother interface with the spacer coupling layer126. This smoother interface increases the strength of the antiferromagnetic coupling between the pinned layer124and the reference layer122, which correlates to an increase in stability of the MR sensor130.

Using a magnetic amorphous material rather than a crystalline material for the pinned layer124also allows for a smoother interface between the pinned layer124and an adjacent antiferromagnetic (AFM) layer136. The AFM layer136biases the magnetic orientation of the pinned layer124in a direction perpendicular to an air-bearing surface (ABS) of the MR sensor130. A stronger biasing of the pinned layer124can be achieved when the interface with the AFM layer136is smooth, rather than rough.

A capping layer128is in contact with the AFM layer136and serves to magnetically decouple the AFM layer136from the adjacent shield element114.

In at least one implementation, the amorphous magnetic material does not include a glass-former. A glass former may be, for example, an element conducive to the occurrence of a glass transition in an amorphous solid material. Glass formers include, without limitation, silicon, boron, germanium, titanium, aluminum, zirconium, beryllium, magnesium, zinc, calcium, lead, lithium, sodium, and potassium. Excluding such glass-former elements from the magnetic amorphous alloy may permit the alloy to exhibit an increased magnetic moment as compared to the same or similar alloys including glass formers. This increase in magnetic moment can translate to an increase in sensor stability. Excluding the glass—former elements from the magnetic amorphous alloy also improves the thermal stability of the amorphous layer. Magnetic amorphous alloys that include glass formers may lack stability and crystalize during annealing processes.

FIG. 2Aillustrates an ABS-facing view of another example MR sensor200including a SAF structure including amorphous magnetic material. The MR sensor200includes a sensor stack232positioned between side shield elements216and218. The side shields216and218are positioned adjacent to the sensor stack232in the cross-track (x-direction), and may be made of soft or hard magnetic material.

A leading edge of the sensor stack232is directly adjacent to a first shield element212, while a trailing edge of the sensor stack is232is directly adjacent to a synthetic antiferromagnetic (SAF) structure including a pinned layer stack224, a reference layer stack222, and a spacer coupling layer226. The SAF structure is magnetically coupled to the side shields216and218.

Each of the pinned layer stack224and the reference layer stack222includes multiple, alternating layers of crystalline ferromagnetic material and amorphous ferromagnetic material. For example, the pinned layer stack224includes two amorphous ferromagnetic layers252and254, each interleaved between a pair of crystalline ferromagnetic layers (e.g., crystalline magnetic layers240,242, and244). Likewise, the reference layer stack222includes two amorphous ferromagnetic layers258and260interleaved between layers of crystalline ferromagnetic layers246,248, and250. Other implementations may include fewer or greater numbers of alternating crystalline ferromagnetic and amorphous ferromagnetic layers.

The crystalline ferromagnetic layers in each of the pinned layer stack224and the reference layer stack222may be, for example, Ni, Co, NiFe, or CoFe. The amorphous ferromagnetic material is a magnetic amorphous alloy including a ferromagnetic material (such as Ni, Co, NiFe, or CoFe) and a refractory material (such as Ta, Nb, Hf, and Zr). In one implementation, the amorphous ferromagnetic material includes between 0 and about 30% of the refractory material, or enough to ensure that the resulting material is amorphous.

In one implementation, the crystalline ferromagnetic layers240,242,244,246,248, and250are layers of NiFe and the amorphous ferromagnetic layers252,254,258, and260are layers of CoFeX, where X is a refractory material. In another implementation, the amorphous ferromagnetic layers252,254,258, and260are layers of CoFeNb.

Depending on design criteria, the z-direction thickness of the crystalline ferromagnetic layers (e.g., the crystalline ferromagnetic layer240) is about 5 to 10 nm and the z-direction thickness of the amorphous ferromagnetic layers (e.g., the amorphous ferromagnetic layer252) is about 0.2 to 3 nm.

The layers in the pinned layer stack224are magnetically coupled together and magnetically biased by an AFM layer236in a direction indicated by arrows inFIG. 2A. Likewise, the layers in the reference layer stack222are magnetically coupled together in a direction opposite the magnetic orientation of the pinned layer stack224. A capping layer228magnetically separates the SAF structure from a second shield element214. Other features of the MR sensor200not explicitly described may be the same or similar to features of the MR sensor discussed with respect toFIG. 1.

Inclusion of the amorphous ferromagnetic layers between the crystalline ferromagnetic layers inFIG. 2Amay break the grain growth in the crystalline ferromagnetic layers and provide for a smoother interface between the spacer coupling layer226and the directly adjacent crystalline ferromagnetic layers244and246. This smoother interface provides for increased coupling strength across the interface that is achieved without degradation to the coupling between the crystalline ferromagnetic layers. In an alternate implementation illustrated inFIG. 2B, amorphous alloy layers262,264are in contact with the spacer coupling layer226. In another alternate implementation illustrated inFIG. 2C, an amorphous alloy layer266is in contact with the AFM layer236.

In addition to the above-described advantages of the MR sensor200, the alternating layers of crystalline ferromagnetic material and amorphous ferromagnetic material allow for an increase in the strength of the pinning field between the AFM layer236and the directly adjacent pinned layer stack224, further boosting stability of the MR sensor200.

FIG. 3illustrates an ABS-facing view of another example MR sensor300including a first SAF structure334and a second SAF structure350. Each of the first SAF structure334and the second SAF structure350include a magnetic amorphous alloy formed from a ferromagnetic material and a refractory material. The MR sensor300includes a sensor stack332sandwiched between side shield elements316and318. The side shields316and318are positioned adjacent to the sensor stack332in the cross-track (x-direction), and may be made of soft or hard magnetic material.

A trailing edge of the sensor stack is332is adjacent to the first SAF structure334. The first SAF structure334includes a pinned layer324, a reference layer322, and a spacer coupling layer326. The pinned layer324is antiferromagnetically coupled to the reference layer322by way of an RKKY coupling provided by the spacer coupling layer326. A first AFM layer336magnetically biases the pinned layer324, and a capping layer328magnetically separates the first SAF structure from a first shield element314.

A leading edge of the sensor stack is332is adjacent to the second SAF structure350. Like the first SAF structure334, the second SAF structure350includes a pinned layer340, a reference layer338, and a spacer coupling layer342. The pinned layer340is antiferromagnetically coupled to the reference layer338by way of an RKKY coupling provided by the spacer coupling layer342. A second AFM layer344magnetically biases the pinned layer340, and a seeding layer346magnetically separates the second SAF structure350from a second shield element312. In another implementation, at least one of the first SAF structure334and the second SAF structure350is a laminated structure.

In another implementation, the MR sensor300includes the second SAF structure350, but excludes the first SAF structure334.

FIG. 4illustrates magnetization behavior in the easy and hard axis (i.e., the axes easiest and hardest to magnetically rotate) for an amorphous ferromagnetic layer of CoFeNb sheet film under an applied magnetic field. In the hard axis, where the magnetic field is zero (at the origin), there is no magnetization. However, the magnetization of the amorphous ferromagnetic material increases along with an applied magnetic field until a saturation point, where the applied magnetic field reaches approximately ±50 Oersteds.

FIG. 5illustrates magnetization behavior in the easy and hard axis for a crystalline ferromagnetic of NiFe sheet film under a magnetic field. The layer of NiFe has a thickness of about 10 nm, which is the same or substantially similar to the thickness of the CoFeNb sheet film utilized to produce the data illustrated inFIG. 4. In the hard axis, under an applied magnetic field, the magnetization of the crystalline ferromagnetic material increases until a saturation point at approximately ±5 Oersteds.

Together,FIGS. 4 and 5demonstrate that fully magnetizing CoFeNb has a higher magnetic anisotropy field (Hk), which requires an applied field of about ten times the strength of the field required to fully saturate NiFe in the hard axis. Thus, an SAF shield including NiFe can be more easily influenced by stray magnetic fields than CoFeNb. Additionally, CoFeNb has a higher magnetic moment than NiFe, which contributes to increased sensor resolution when used as a shield.

FIG. 6illustrates magnetization behavior for two different SAF structures under an applied magnetic field. A first SAF structure, with data shown by line602, includes layers of NiFe antiferromagnetically coupled together. A second SAF structure, with data shown by line604, includes layers of CoFeNb antiferromagnetically coupled together. The plot shows that the SAF structure including the CoFeNb has a higher saturation field, which is indicative of an improved RKKY coupling. Also, the data shows that the SAF structure including the CoFeNb has a higher nucleation field than the SAF structure including the NiFe.

The above specification, examples, and data provide a complete description of the structure and use of exemplary implementations of the invention. Since many implementations of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.