阅读说明：本技术 具有多层合成铁磁体自由层的读取器 (Reader with multilayer synthetic ferromagnetic free layer ) 是由 A·多布瑞宁 P·G·麦卡弗蒂 K·A·麦克尼尔 于 2021-03-25 设计创作，主要内容包括：本申请公开了具有多层合成铁磁体自由层的读取器。一种装置,包括读取传感器,该读取传感器具有三层合成铁磁体自由层和靠近该三层合成铁磁体自由层定位的至少一个侧屏蔽件。该至少一个侧屏蔽件在第一方向上提供偏置磁场以将该三层合成铁磁体自由层偏置。(The application discloses a reader having a multilayer synthetic ferromagnetic free layer. An apparatus includes a read sensor having a tri-layer synthetic ferromagnetic free layer and at least one side shield positioned proximate the tri-layer synthetic ferromagnetic free layer. The at least one side shield provides a bias magnetic field in a first direction to bias the tri-layer synthetic ferromagnetic free layer.)

1. A reader, comprising:

a read sensor, comprising:

a multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

2. The reader of claim 1 wherein the multi-layer synthetic ferromagnetic free layer comprises a three-layer synthetic ferromagnetic free layer.

3. The reader of claim 2, further comprising a Synthetic Antiferromagnetic (SAF) structure under the tri-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

4. The reader of claim 3, wherein the three synthetic ferromagnetic free layers comprise a bottom magnetic layer over the tunneling barrier layer, an intermediate magnetic layer over the bottom magnetic layer, and a top magnetic layer over the intermediate magnetic layer, and wherein the bottom magnetic layer and the intermediate magnetic layer are separated by a first spacer layer, and the intermediate magnetic layer and the top magnetic layer are separated by a second spacer layer.

5. The reader of claim 4, further comprising at least one side shield providing a bias magnetic field in the first direction.

6. A method of forming a reader, comprising:

forming a read sensor by:

forming a multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

7. The method of claim 6, wherein forming the multi-layer synthetic ferromagnetic free layer comprises forming a three-layer synthetic ferromagnetic free layer.

8. The method of claim 7, further comprising forming a Synthetic Antiferromagnetic (SAF) structure below the tri-layer synthetic ferromagnetic free layer and forming a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

9. An apparatus, comprising:

a read sensor comprising a three-layer synthetic ferromagnetic free layer; and

at least one side shield providing a bias magnetic field in a first direction to bias the tri-layer synthetic ferromagnetic free layer.

10. The apparatus of claim 9, further comprising a Synthetic Antiferromagnetic (SAF) structure below the tri-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

Disclosure of Invention

In one embodiment, a reader is provided. The reader includes a read sensor having a multi-layer synthetic ferromagnetic free layer. The multilayer synthetic ferromagnetic free layer has a non-zero net magnetization that biases the multilayer synthetic ferromagnetic free layer.

In another embodiment, a method of forming a reader is provided. The method includes forming a read sensor by forming a multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

In yet another embodiment, an apparatus is provided. The apparatus includes a read sensor having a trilayer synthetic ferromagnetic free layer and at least one side shield. The at least one side shield provides a bias magnetic field in a first direction to bias the tri-layer synthetic ferromagnetic free layer.

Other features and advantages that characterize embodiments of the present disclosure will be apparent upon reading the following detailed description and review of the associated drawings.

Drawings

FIG. 1 is a schematic diagram of a data storage system including a data storage medium and a head for reading data from and/or writing data to the data storage medium.

FIG. 2 is a schematic diagram of a cross-section of one embodiment of a recording head reading from and writing to a storage medium.

Fig. 3A is a supporting surface view of a magnetic playback device (reproducing device) according to one embodiment.

FIG. 3B is a cross-sectional view of a portion of the embodiment of the magnetic playback device of FIG. 3A.

Fig. 4 and 5 are graphs of results obtained from micromagnetic simulations of readers having a trilayer synthetic ferromagnetic free layer.

Detailed Description

Embodiments of the present disclosure relate to readers that employ a multilayer synthetic ferromagnet as its free layer. However, before providing additional details regarding different embodiments, a description of an illustrative operating environment is provided below.

FIG. 1 shows an illustrative operating environment in which certain embodiments disclosed herein may be incorporated. The operating environment shown in FIG. 1 is for illustration only. Embodiments of the present disclosure are not limited to any particular operating environment, such as the operating environment illustrated in fig. 1. Embodiments of the present disclosure are illustratively practiced in any number of different types of operating environments.

It should be noted that the same or similar elements are provided with the same reference numerals in different drawings. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. Unless otherwise indicated, serial numbers (e.g., first, second, third, etc.) are used to distinguish or identify different elements or steps in a group of elements or steps, and do not provide a sequential or numerical limitation to the elements or steps of embodiments thereof. For example, "first," "second," and "third" elements or steps need not be present in that order, and embodiments thereof need not be limited to three elements or steps. It should also be understood that, unless otherwise indicated, any label such as "left", "right", "front", "back", "top", "bottom", "forward", "reverse", "clockwise", "counterclockwise", "up", "down", or other similar terms, such as "above", "below", "rear", "front", "vertical", "horizontal", "proximal", "distal", "intermediate", and the like, are used for convenience and are not intended to denote any particular fixed position, orientation, or direction, for example. Rather, such labels are used to reflect, for example, relative position, orientation, or direction. It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

It will be understood that when an element is referred to as being "connected," "coupled," or "attached" to another element, it can be directly connected, coupled, or attached to the other element or it can be indirectly connected, coupled, or attached to the other element with intervening elements or elements present. In contrast, when an element is referred to as being "directly connected," "directly coupled," or "directly attached" to another element, there are no intervening elements present. The figures illustrating direct connections, couplings or attachments between elements also include embodiments in which elements are indirectly connected, coupled or connected to one another.

FIG. 1 is a schematic diagram of a data storage device 100 including a data storage medium and a head for reading data from and/or writing data to the data storage medium. In data storage device 100, head 102 is positioned over storage medium 104 to read data from data storage medium 104 and/or write data to data storage medium 104. In the illustrated embodiment, data storage medium 104 is a rotatable disk or other magnetic storage medium that includes one or more magnetic storage layers. For read and write operations, a spindle motor 106 (shown schematically) rotates the media 104 as indicated by arrow 107, and an actuator mechanism 110 positions the head 102 between an inner diameter 108 and an outer diameter 109 relative to data tracks 114 on the rotating media 104. Both the spindle motor 106 and the actuator mechanism 110 are connected to driver circuitry 112 and are operated by the driver circuitry 112 (shown schematically). The head 102 is coupled to the actuator mechanism 110 by a suspension assembly that includes a load beam 120 connected to an actuator arm 122 of the mechanism 110, for example, by a swaged connection. Although FIG. 1 shows a single load beam coupled to the actuator mechanism 110, additional load beams 120 and heads 102 may be coupled to the actuator mechanism 110 to read data from or write data to multiple disks in a disk stack. The actuator mechanism 110 is rotationally coupled to a frame or platform (not shown) by a bearing 124 for rotation about an axis 126. Rotation of the actuator mechanism 110 moves the head 102 in the cross-track direction as indicated by arrow 130.

The head 102 includes one or more transducer elements (not shown in fig. 1) coupled to head circuitry 132 by flex circuits 134. Details regarding elements of the head, such as 102, are provided below in connection with FIG. 2.

FIG. 2 is a schematic diagram illustrating a cross-sectional view of portions of a recording head 200 and a data storage medium 250 taken along a plane substantially perpendicular to a bearing surface (e.g., Air Bearing Surface (ABS))202 of the recording head 200. The recording head elements shown in fig. 2 are illustratively included in a recording head, such as recording head 102 in fig. 1. Medium 250 is illustratively a data storage medium, such as medium 104 in fig. 1. Those skilled in the art will recognize that the recording head and the recording medium collectively include other components. Embodiments of the present disclosure are not limited to any particular recording head and recording medium. Embodiments of the present disclosure may be practiced in different types of recording heads and recording media.

Recording head 200 includes write pole 205, magnetizing coil 210, return pole 215, top shield 218, read transducer 220, bottom shield 222, and wafer cladding 224. The storage medium 250 includes a recording layer 255 and a bottom layer 260. Storage medium 250 rotates in the direction shown by arrow 265. Arrow 265 is illustratively a direction of rotation, such as arrow 107 in fig. 1.

In an embodiment, a current is passed through the coil 210 to generate a magnetic field. The magnetic field passes from write pole 205, through recording layer 255, into underlayer 260, and then crosses over to return pole 215. The magnetic field illustratively records a magnetization pattern 270 in recording layer 255. Read transducer 220 senses or detects the magnetization pattern in recording layer 255 and is used to retrieve information previously recorded to layer 255.

To address certain challenges discussed below, the read transducer or reader 220 includes a read sensor that employs a multilayer synthetic ferromagnetic 230 as its free layer. In different reader embodiments, the layers of the read sensor may be stacked along the track direction (e.g., the z-direction in FIG. 2). The track width direction is perpendicular to the z-direction or track direction (e.g., cross-track direction, in FIG. 2 the x-direction). The y-direction in fig. 2 is then defined as the direction perpendicular to both x and z, which is the stripe height direction. The challenges presented by new data storage technologies, and details regarding how to solve such challenges with sensors having multi-layer synthetic ferromagnetic free layers, are described below in conjunction with fig. 3A-5.

Recent data storage technologies, such as Heat Assisted Magnetic Recording (HAMR), drive higher and higher read along-track and cross-track resolutions. This means a reduction in the free layer size, which leads to a degradation of the signal-to-noise ratio (SNR) due to higher magnetic noise. Furthermore, the reduction of the free layer thickness means that the Spin Transfer Torque (STT) contributes more to the noise, thus further reducing the signal-to-noise ratio. To address such challenges, the structure and composition of the free layer is adjusted in embodiments of the present disclosure.

In one embodiment, the free layer is a composite structure that includes three Ferromagnetic (FM) layers separated by metal interlayers that provide Antiferromagnetic (AFM) coupling between adjacent FM layers, such as in a Synthetic Antiferromagnetic (SAF) structure. Such a trilayer represents a synthetic ferromagnetic structure because it has a non-zero net magnetization to later provide a bias to the free layer through the side shields. A three-layer synthetic ferromagnetic free layer embodiment is described below in conjunction with fig. 3A and 3B.

FIG. 3A is a schematic block diagram illustrating a bearing surface view of an example embodiment of a read head 300 including a synthetic ferromagnetic free layer structure. FIG. 3B is a cross-sectional view of portions of the read head 300 along line A-A' of FIG. 3A. Referring to fig. 3A and 3B, read head 300 includes a magnetoresistive sensor 302 positioned between top shield 218 and bottom shield 222. Top and bottom shields 218 and 222, which may be made of a material having a high magnetic permeability, reduce or substantially block external magnetic fields (such as, for example, those from adjacent positions on a data disk) from affecting magnetoresistive sensor 302, thereby improving the performance of magnetoresistive sensor 302. In one implementation, top and bottom shields 218 and 222 allow magnetic fields from bits directly below magnetoresistive sensor 302 to affect magnetoresistive sensor 302 for reading. It should be noted that the top shield 218 may be a single fixed layer (pinned layer) or a bottom layer of the SAF structure.

The magnetoresistive sensor 302 includes a plurality of layers including a sensor AFM layer 304, a sensor stacked SAF structure 306, a tunneling barrier layer 308, and a tri-layer synthetic ferromagnetic free layer 310. A stack cap layer 311 may also be included over the tri-layer synthetic ferromagnetic free layer 310.

In the embodiment shown in FIG. 3A, the sensor SAF structure 306 includes a fixed layer 316, a thin separation layer 318, and a reference layer 320, the thin separation layer 318 may include a metal such as ruthenium (Ru) in some embodiments. The magnetic moment of each of the fixed layer 316 and the reference layer 320 is not allowed to rotate under a magnetic field in the range of interest (e.g., a magnetic field generated by a data bit stored on a data disk). The magnetic moments of the reference layer 320 and the pinned fixed layer 316 are generally oriented perpendicular to the plane of FIG. 3A (e.g., the y-direction) and anti-parallel to each other.

As indicated above, instead of employing a bulk/solid free layer, the sensor 302 includes a three-layer synthetic ferromagnetic free layer 310. In the embodiment of fig. 3A and 3B, the tri-layer synthetic ferromagnetic free layer 310 includes a bottom FM layer 310A, a middle FM layer 310B, and a top FM layer 310C. The bottom FM layer 310A and the middle FM layer 310B are separated by a first spacer layer 312A, and the middle FM layer 310B and the top FM layer 310C are separated by a second spacer layer 312B. The spacer layers 312A and 312B may be formed of a metal such as ruthenium (Ru). In the embodiment of fig. 3A and 3B, the magnetic moments of layers 310A, 310B, and 310C are oriented generally parallel to the plane of fig. 3A (e.g., in the x-direction), with the magnetization orientation of layer 310B opposite the magnetization orientation of layers 310A and 310C. The magnetization orientations of the bottom magnetic layer 310A and the top magnetic layer 310B are set by the side shields 322. However, the side shield 322 is biased small enough so that the magnetic moment of the tri-layer synthetic ferromagnetic free layer 310 can change in response to an applied magnetic field (such as the magnetic field of a data bit stored on a data disk). In some embodiments, the side shield 322 is formed from one or more layers of soft magnetic material (e.g., a material that can be easily magnetized and demagnetized at relatively low magnetic fields). The soft magnetic material is an alloy containing Ni and Fe or Co and Fe. Magnetoresistive sensor 302 is separated and electrically isolated from side-bias magnet 322 by an isolation layer 324 (comprising, for example, an insulating material). As shown in FIG. 3A, isolation layer 324 may also be present in other areas of head 300. It should be noted that in some embodiments, a side-biased permanent magnet may be used in place of the side shield 322. In an embodiment of the present disclosure, the spontaneous magnetization (Ms) of the material used for the middle magnetic layer 310B is lower (e.g., significantly lower) than the spontaneous magnetization of the material of the layers 310A and 310C to avoid the side shield 322 from significantly reducing the free layer bias.

In some embodiments, the sensor 302 may utilize Tunneling Magnetoresistance (TMR). in embodiments utilizing the TMR effect, a tunneling barrier layer 308 separates the SAF structure 306 from a tri-layer synthetic ferromagnetic free layer 310. The tunneling barrier layer 308 is sufficiently thin such that quantum mechanical electron tunneling occurs between the reference layer 320 and the tri-layer synthetic ferromagnetic free layer 310 in the SAF structure 306. Electron tunneling is electron spin dependent, such that the magnetic response of magnetoresistive sensor 302 is a function of the relative orientation and spin polarization of SAF structure 306 and tri-layer synthetic ferromagnetic free layer 310. The highest probability of electron tunneling occurs when the magnetic moments of the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310 are parallel and the lowest probability of electron tunneling occurs when the magnetic moments of the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310 are anti-parallel. Accordingly, the resistance of magnetoresistive sensor 302 changes in response to the applied magnetic field. The data bits on the data disks in the disk drive may be magnetized in a direction perpendicular to the plane of FIG. 3A, either into the plane of the drawing or out of the plane of the drawing. Thus, as magnetoresistive sensor 302 passes over a data bit, the magnetic moment of trilayer synthetic ferromagnetic free layer 310 rotates into or out of the plane of FIG. 3A, thereby changing the resistance of magnetoresistive sensor 302. Accordingly, a value (e.g., 1 or 0) of a bit sensed by magnetoresistive sensor 302 may be determined based on a current flowing from a first electrode (not shown) to a second electrode (not shown) connected to magnetoresistive sensor 302.

One advantage of the above design over a standard (e.g., bulk) free layer is that the magnetization of the free layer is better confined in the XY plane due to the increased shape anisotropy of each of the component layers. This improves the linearity resolution of the reader by improving the consistency of the response of the free layer to the media field by reducing the sensitivity to media field components that are not aligned along the Y-direction. Another advantage is that the effect of Spin Transfer Torque (STT) on noise is reduced. The STT originates from spin polarized current near the tunneling barrier, and the STT contributes significantly to magnetic noise. One technique for depolarizing current is to use an SAF structure. Thus, the above design provides a reduced current polarization for the middle FM layer 310B and a further reduced STT for the top FM layer 310C, thereby reducing the STT contribution to noise and improving SNR.

Micromagnetic simulations were performed on the above described devices. The following parameters were used: reader width (X dimension of free layer 310) -28 nanometers (nm); stripe height (Y dimension of free layer 310) -30 nm; thickness (Z dimension of free layer 310) -3 nm; ms-1500emu/cc of the fixed layer 316; spacer layer 318 thickness-3 nm; ms-1500emu/cc for reference layer 320; layer 310A is-3 nm thick; ms-1300emu/cc for layer 310A; layer 310B is-2 nm thick; ms-xemu/cc for layer 310B (where x varies from 100emu/cc to 1000 emu/cc); layer 310C is-2 nm thick; ms-1300emu/cc for layer 310C, and Ms-800emu/cc for shields 218, 222, and 322. Fig. 4 shows the linear resolution (pulse width 50(PW50)) of the reader as a function of Ms for the middle FM layer (e.g., 310B). This is compared to the PW50 value for a standard reader with the same geometry and dimensions but a single free layer, which PW50 value equals 25.3 nm. As can be clearly seen from fig. 4, the gain in PW50 varies from greater than 2nm for the high Ms layer 310B to about 1nm for the low Ms layer 310B.

Fig. 5 is a graph showing the corresponding variability of signal-to-noise ratio (SNR) versus Ms of an intermediate FM layer (e.g., 310B). This is compared to a reference SNR value of 18.8 decibels (dB). Without considering the STT effect here, the magnetic noise only originates from thermal fluctuations of the magnetization at room temperature. In fig. 5, it can be seen that an SNR gain of about 1db makes achievable for the low Ms layer 310B. The reduced STTs in layers 310B and 310C may further improve SNR.

In readers of the type shown in fig. 3A and 3B, the signal amplitude is increased by 6% and the asymmetry is increased by 3% compared to a reference reader with a large free layer. Also, cross-track resolution in readers of the type shown in FIGS. 3A and 3B remains unchanged relative to the cross-track resolution of a reference reader having a large free layer.

Other parameters that may be varied for optimal reader performance include the thickness of layers 310A-310C, Ms of layer 310B, the strength of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupled via spacer layers 312A and 312B in the synthetic ferromagnetic free layer 310, and the bias field defined by the side shield 322 and Ms of the side shield 322-free layer gap.

As described above, the synthetic ferromagnetic free layer may include three or more layers, and the structural layers of the multi-layer free layer may have different Ms values. In some embodiments, the component layer(s) whose magnetization is set by the bias field of the side shield can have an Ms that is greater than approximately 1 Tesla (T). In such embodiments, CoFe alloys having different compositions may be used for the layers. Further, in such embodiments, the layer(s) whose magnetization is oriented opposite the bias field of the side shield can have an Ms that does not exceed 1T. CoFeX alloys may be used to adjust the magnetization to a predetermined level, where X may be Ta, Zr, Hf, or other doping element, and where the composition of X may vary between 1-40%. NiFe alloys may also be used.

The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments will be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, these illustrations are merely representational and may be drawn to scale. Some proportions within the illustrations may be exaggerated, while other proportions may be minimized. The present disclosure and figures are, therefore, to be regarded as illustrative rather than restrictive.

One or more embodiments of the present invention may be referred to herein, individually and/or collectively, by the term "invention" merely for convenience and without intending to limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. Any subsequent adaptations or variations of the various embodiments, which are intended to be covered by the present disclosure, as well as other embodiments not specifically described herein, will be apparent to those of skill in the art upon reading the foregoing description.

The abstract of the disclosure is provided to comply with 37c.f.r. § 1.72(b), and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing detailed description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This invention is not to be interpreted as reflecting an intention that the claimed embodiments employ more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments.

It is intended that the above-disclosed subject matter be regarded as illustrative rather than restrictive, and that the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Further examples are:

example 1. a reader, comprising: a read sensor, comprising: a multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

Example 2. the reader of example 1, wherein the multi-layer synthetic ferromagnetic free layer comprises three layers of synthetic ferromagnetic free layers.

Example 3. the reader of example 2, further comprising a Synthetic Antiferromagnetic (SAF) structure under the tri-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

Example 4. the reader of example 3, wherein the three synthetic ferromagnetic free layers comprise a bottom magnetic layer over the tunneling barrier layer, an intermediate magnetic layer over the bottom magnetic layer, and a top magnetic layer over the intermediate magnetic layer, and wherein the bottom magnetic layer and the intermediate magnetic layer are separated by a first spacer layer, and the intermediate magnetic layer and the top magnetic layer are separated by a second spacer layer.

Example 5. the reader of example 4, further comprising at least one side shield to provide a bias magnetic field in the first direction.

Example 6. the reader of example 5, wherein the bottom magnetic layer of the tri-layer synthetic ferromagnetic free layer and the top magnetic layer of the tri-layer synthetic ferromagnetic free layer have magnetization orientations set by the at least one side shield in the first direction.

Example 7. the reader of example 6, wherein the middle magnetic layer of the tri-layer synthetic ferromagnetic free layer comprises a magnetization orientation in a second direction, the magnetization orientation opposing the bias magnetic field in the first direction.

Example 8. the reader of example 4, wherein a spontaneous magnetization of a material of the middle magnetic layer of the tri-layer synthetic ferromagnetic free layer is lower than a spontaneous magnetization of a material of the bottom magnetic layer of the tri-layer synthetic ferromagnetic free layer and lower than a spontaneous magnetization of the top magnetic layer of the tri-layer synthetic ferromagnetic free layer.

Example 9. a method of forming a reader, comprising: forming a read sensor by: forming a multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

Example 10 the method of example 9, wherein forming the multi-layer synthetic ferromagnetic free layer comprises forming a three-layer synthetic ferromagnetic free layer.

Example 11 the method of example 10, further comprising forming a Synthetic Antiferromagnetic (SAF) structure under the tri-layer synthetic ferromagnetic free layer, and forming a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

Example 12. the method of example 11, wherein forming the tri-layer synthetic ferromagnetic free layer includes forming a bottom magnetic layer over the tunneling barrier layer, forming a first spacer layer over the bottom magnetic layer, forming an intermediate magnetic layer over the first spacer layer, forming a second spacer layer over the intermediate magnetic layer, and forming a top magnetic layer over the second spacer layer.

Example 13. the method of example 12, further comprising forming at least one side shield to provide a bias magnetic field in a first direction.

The method of example 13, further comprising setting, by the at least one side shield, a magnetization orientation of both the bottom magnetic layer of the tri-layer synthetic ferromagnetic free layer and the top magnetic layer of the tri-layer synthetic ferromagnetic free layer in the first direction.

Example 15 the method of example 14, further comprising setting a magnetization orientation of the middle magnetic layer of the tri-layer synthetic ferromagnetic free layer in a second direction, the magnetization orientation opposing the bias magnetic field in the first direction.

Example 16. the reader of example 12, further comprising forming the middle magnetic layer of the tri-layer synthetic ferromagnetic free layer with a material having a spontaneous magnetization that is lower than a spontaneous magnetization of a material used to form the bottom magnetic layer of the tri-layer synthetic ferromagnetic free layer and lower than a spontaneous magnetization of a material used to form the top magnetic layer of the tri-layer synthetic ferromagnetic free layer.

An apparatus, comprising: a read sensor comprising a three-layer synthetic ferromagnetic free layer; and at least one side shield providing a bias magnetic field in a first direction to bias the tri-layer synthetic ferromagnetic free layer.

The apparatus of example 17, further comprising a Synthetic Antiferromagnetic (SAF) structure under the tri-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the tri-layer synthetic ferromagnetic free layer and the SAF structure.

The apparatus of example 18, wherein the three synthetic ferromagnetic free layers include a bottom magnetic layer over a tunneling barrier layer, an intermediate magnetic layer over the bottom magnetic layer, and a top magnetic layer over the intermediate magnetic layer, and wherein the bottom magnetic layer and the intermediate magnetic layer are separated by a first spacer layer, and the intermediate magnetic layer and the top magnetic layer are separated by a second spacer layer.

Example 20. the apparatus of example 19, wherein: the bottom magnetic layer of the tri-layer synthetic ferromagnetic free layer and the top magnetic layer of the tri-layer synthetic ferromagnetic free layer have magnetization orientations set by the at least one side shield in the first direction; and the middle magnetic layer of the tri-layer synthetic ferromagnetic free layer comprises a magnetization orientation in a second direction opposite the bias magnetic field in the first direction.