Reader with multi-layer synthetic ferromagnetic free layer

Abstract

The present application discloses a reader with a multi-layer synthetic ferromagnetic free layer. A device includes a reading sensor having a three-layer synthetic ferromagnetic free layer and at least one side shield positioned near the three-layer synthetic ferromagnetic free layer. The at least one side shield provides a bias magnetic field in a first direction to bias the three-layer synthetic ferromagnetic free layer.

Description

Technical Field

[0001] The present application relates to data storage media and, more particularly, to readers having a multi-layer synthetic ferromagnetic free layer. Background Art

[0002] Recent data storage technologies, such as heat-assisted magnetic recording (HAMR), have driven higher and higher read along-track and across-track resolutions. This implies a reduction in the size of the free layer, which results in a degradation of the signal-to-noise ratio (SNR) due to higher magnetic noise. Furthermore, a reduction in the thickness of the free layer implies a higher contribution of the spin transfer torque (STT) to the noise, thus further reducing the signal-to-noise ratio. To address such challenges, the structure and composition of the free layer are adjusted in embodiments of the present disclosure. Summary of the invention

[0003] In one embodiment, a reader is provided. The reader includes a read sensor having a multi-layer synthetic ferromagnetic free layer. The multi-layer synthetic ferromagnetic free layer has a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

[0004] 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.

[0005] In yet another embodiment, a device is provided. The device includes a read sensor having a three-layer 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 three-layer synthetic ferromagnetic free layer.

[0006] Other features and advantages that characterize embodiments of the present disclosure will become apparent upon reading the following detailed description and examining the associated drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 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.

[0008] Figure 2 is a schematic diagram of a cross section of one embodiment of a recording head that reads from and writes to a storage medium.

[0009] Figure 3A is a view of a support surface of a magnetic reproducing device according to one embodiment.

[0010] Figure 3B yes Figure 3A A cross-sectional view of a portion of an embodiment of a magnetic playback device.

[0011] Figure 4 and Figure 5 Results from a micromagnetic simulation of a reader with a three-layer synthetic ferromagnetic free layer. DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure are directed to readers that employ a multilayer synthetic ferromagnet as their free layer. However, before providing additional details regarding the various embodiments, a description of an illustrative operating environment is provided below.

[0013] Figure 1 An illustrative operating environment is shown in which certain embodiments disclosed herein may be incorporated. Figure 1 The operating environment shown in FIG. is for illustrative purposes only. The embodiments of the present disclosure are not limited to any particular operating environment, such as Figure 1 Embodiments of the present disclosure may be illustratively practiced in any number of different types of operating environments.

[0014] It should be noted that the same or similar elements use the same reference numerals in different drawings. It should be understood that the terms used herein are only for the purpose of describing a specific embodiment, and the term is not intended to be limited. Unless otherwise indicated, sequence 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 sequence or numerical restrictions for the elements or steps of its embodiments. For example, "first", "second" and "third" elements or steps do not have to appear in this order, and its embodiments do not have to 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", "opposite", "clockwise", "counterclockwise", "up", "down", or other similar terms, such as "above", "below", "after", "before", "vertical", "horizontal", "proximal end", "distal end", "between" etc. are used for convenience and are not intended to represent, for example, any specific fixed position, orientation or direction. On the contrary, 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.

[0015] It should be understood that when an element is referred to as being "connected," "coupled," or "attached" to another element, it may be directly connected, coupled, or attached to the other element, or it may be indirectly connected, coupled, or attached to the other element in which there may be intervening elements or intermediate elements. Conversely, when an element is referred to as being "directly connected," "directly coupled," or "directly attached" to another element, there are no intervening elements. The drawings illustrating direct connections, couplings, or attachments between elements also include embodiments in which elements are indirectly connected, coupled, or connected to each other.

[0016] Figure 1 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 the data storage device 100, a head 102 is positioned above a storage medium 104 to read data from and / or write data to the data storage medium 104. In the illustrated embodiment, the data storage medium 104 is a rotatable disk or other magnetic storage medium including one or more magnetic storage layers. For read and write operations, a spindle motor 106 (shown schematically) rotates the medium 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 a data track 114 on the rotating medium 104. Both the spindle motor 106 and the actuator mechanism 110 are connected to and operated by a driver circuitry 112 (shown schematically). The head 102 is coupled to the actuator mechanism 110 through a suspension assembly that includes a load beam 120 connected to an actuator arm 122 of the mechanism 110, such as by a swaged connection. Figure 1 A single load beam is shown coupled to the actuator mechanism 110, but 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) via bearings 124 for rotation about axis 126. Rotation of the actuator mechanism 110 moves the head 102 in a cross-track direction as indicated by arrow 130.

[0017] The head 102 includes one or more transducer elements (eg, Figure 1 ). Figure 2 Details are provided regarding elements of the head, such as 102 .

[0018] Figure 2is a schematic diagram showing cross-sectional views of portions of the recording head 200 and the data storage medium 250 taken along a plane substantially perpendicular to a bearing surface (eg, air bearing surface (ABS)) 202 of the recording head 200 . Figure 2 The recording head elements shown in illustratively include a recording head (such as Figure 1 The recording head 102 in the recording head 102). The medium 250 is illustratively a data storage medium such as Figure 1 The medium 104 in the recording head. Those skilled in the art will recognize that the recording head and the recording medium together include other components. The embodiments of the present disclosure are not limited to any particular recording head and recording medium. The embodiments of the present disclosure can be practiced in different types of recording heads and recording media.

[0019] Recording head 200 includes write pole 205, magnetizing coil 210, return pole 215, top shield 218, read transducer 220, bottom shield 222, and wafer cover 224. Storage medium 250 includes recording layer 255 and bottom layer 260. Storage medium 250 rotates in the direction indicated by arrow 265. Arrow 265 is illustratively a rotation direction, such as Figure 1 Arrow 107 in FIG.

[0020] In an embodiment, current is passed through coil 210 to generate a magnetic field. The magnetic field passes from write pole 205 through recording layer 255 into bottom layer 260 and then across to return pole 215. The magnetic field illustratively records 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.

[0021] To address some of the challenges discussed below, the read transducer or reader 220 includes a read sensor that uses a multilayer synthetic ferromagnet 230 as its free layer. In various reader embodiments, the layers of the read sensor can be arranged along the track direction (e.g., Figure 2 The track width direction is perpendicular to the z direction or the track direction (e.g., the cross-track direction, in Figure 2 is the x direction). Figure 2 The y direction in is then defined as being perpendicular to both the x and z directions, which is the direction of the stripe height. Figure 3A-Figure 5 Details related to the challenges posed by new data storage technologies and how sensors with multi-layer synthetic ferromagnetic free layers can be used to address such challenges are described.

[0022] In one embodiment, the free layer is a composite structure that includes three ferromagnetic (FM) layers separated by a metal spacer layer that provides antiferromagnetic (AFM) coupling between adjacent FM layers (such as in a synthetic antiferromagnetic (SAF) structure). Such three layers represent a synthetic ferromagnetic structure because they have a non-zero net magnetization and bias is then provided to the free layer through the side shields. Figure 3A and Figure 3B A three-layer synthetic ferromagnetic free layer embodiment is described.

[0023] Figure 3A is a schematic block diagram illustrating a support surface view of an example embodiment of a read head 300 including a synthetic ferromagnetic free layer structure. Figure 3B The parts of the reading head 300 are along Figure 3A A cross-sectional view of the line A-A'. Figure 3A and Figure 3B , the read head 300 includes a magnetoresistive sensor 302 located between a top shield 218 and a bottom shield 222. The 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 bits on the data disk) from affecting the magnetoresistive sensor 302, thereby improving the performance of the magnetoresistive sensor 302. In one implementation, the top and bottom shields 218 and 222 allow magnetic fields from bits directly below the magnetoresistive sensor 302 to affect the magnetoresistive sensor 302, thereby performing a read. It should be noted that the top shield 218 may be a single pinned layer or a bottom layer of the SAF structure.

[0024] Magnetoresistive sensor 302 includes multiple layers including sensor AFM layer 304, sensor stack SAF structure 306, tunneling barrier layer 308, and tri-layer synthetic ferromagnetic free layer 310. Stack cap layer 311 may also be included over tri-layer synthetic ferromagnetic free layer 310.

[0025] exist Figure 3A In the illustrated embodiment, the sensor SAF structure 306 includes a pinned layer 316, a thin spacer layer 318, and a reference layer 320. In some embodiments, the thin spacer layer 318 may include a metal such as ruthenium (Ru). The magnetic moment of each of the pinned layer 316 and the reference layer 320 is not allowed to rotate under a magnetic field in a range of interest (e.g., a magnetic field generated by data bits stored on a data disk). The magnetic moments of the reference layer 320 and the pinned fixed layer 316 are generally perpendicular to the magnetic field. Figure 3A are oriented in the planes of the plane (e.g., the y direction) and are antiparallel to each other.

[0026] As indicated above, instead of employing a bulk / solid free layer, the sensor 302 includes a three-layer synthetic ferromagnetic free layer 310. Figure 3A and Figure 3B In the embodiment of the present invention, the three-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 can be formed of a metal such as ruthenium (Ru). Figure 3A and Figure 3B In the embodiment of the present invention, the magnetic moments of layers 310A, 310B, and 310C are generally parallel to Figure 3A oriented in a plane (e.g., in the x-direction) with the magnetization orientation of layer 310B being opposite to the magnetization orientation of layers 310A and 310C. The magnetization orientation of the bottom magnetic layer 310A and the top magnetic layer 310B is set by the side shield 322. However, the side shield 322 bias is small enough so that the magnetic moment of the three-layer synthetic ferromagnetic free layer 310 can change in response to an applied magnetic field (such as the magnetic field of data bits stored on a data disk). In some embodiments, the side shield 322 is formed of one or more layers of soft magnetic material (e.g., a material that can be easily magnetized and demagnetized under relatively low magnetic fields). The soft magnetic material is an alloy comprising Ni and Fe or Co and Fe. The magnetoresistive sensor 302 is separated and electrically isolated from the side bias magnet 322 by an isolation layer 324 (comprising, for example, an insulating material). As Figure 3A As shown, the isolation layer 324 may also be present in other areas of the head 300. It should be noted that in some embodiments, side bias permanent magnets may be used instead of the side shields 322. In embodiments 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 shields 322 significantly reducing the free layer bias.

[0027] In some embodiments, the sensor 302 can utilize tunneling magnetoresistance (TMR). In embodiments utilizing the TMR effect, a tunneling barrier layer 308 separates the SAF structure 306 from the tri-layer synthetic ferromagnetic free layer 310. The tunneling barrier layer 308 is thin enough so that quantum mechanical electron tunneling occurs between the reference layer 320 in the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310. Electron tunneling is electron spin-dependent, so that the magnetic response of the magnetoresistive sensor 302 is a function of the relative orientation and spin polarization of the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310. The probability of electron tunneling occurring is highest when the magnetic moments of the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310 are parallel, and the probability of electron tunneling occurring is lowest when the magnetic moments of the SAF structure 306 and the tri-layer synthetic ferromagnetic free layer 310 are anti-parallel. Therefore, the resistance of the magnetoresistive sensor 302 changes in response to an applied magnetic field. Data bits on a data disk in a disk drive can be moved in a direction perpendicular to the magnetic field. Figure 3A Therefore, when the magnetoresistive sensor 302 passes a data bit, the magnetic moment of the three-layer synthetic ferromagnetic free layer 310 rotates to Figure 3A in the plane or Figure 3A , thereby changing the resistance of the magnetoresistive sensor 302. Therefore, the value of the bit sensed by the magnetoresistive sensor 302 (e.g., 1 or 0) can be determined based on the current flowing from the first electrode (not shown) to the second electrode (not shown) connected to the magnetoresistive sensor 302.

[0028] One advantage of the above design compared to 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 constituent layer. This improves the consistency of the free layer's response to the dielectric field by reducing sensitivity to dielectric field components that are not aligned along the Y direction, thereby improving the linear resolution of the reader. Another advantage is the reduced contribution of spin transfer torque (STT) to noise. STT originates from spin-polarized currents near the tunneling barrier, and STT contributes significantly to magnetic noise. One technique for depolarizing the current is to use a SAF structure. Therefore, the above design provides reduced current polarization for the middle FM layer 310B and further reduced STT for the top FM layer 310C, thereby reducing the contribution of STT to noise and improving SNR.

[0029] Micromagnetic simulations were performed for the above 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) - 30nm; thickness (Z dimension of free layer 310) - 3nm; Ms of fixed layer 316 - 1500emu / cc; thickness of spacer layer 318 - 3nm; Ms of reference layer 320 - 1500emu / cc; thickness of layer 310A - 3nm; Ms of layer 310A - 1300emu / cc; thickness of layer 310B - 2nm; Ms of layer 310B - xemu / cc (where x varies between 100emu / cc and 1000emu / cc); thickness of layer 310C - 2nm; Ms of layer 310C - 1300emu / cc, and Ms of shields 218, 222 and 322 - 800emu / cc. Figure 4 The linear resolution (Pulse Width 50 (PW50)) of the reader is shown as a function of the Ms of the intermediate FM layer (e.g., 310B). This is compared to the PW50 value of a standard reader with the same geometry and dimensions but a single free layer, which is equal to 25.3 nm. Figure 4 It can be clearly seen that the gain in PW50 varies from more than 2 nm in the high Ms layer 310B to about 1 nm in the low Ms layer 310B.

[0030] Figure 5 is a graph showing the corresponding dependence of the signal-to-noise ratio (SNR) on the Ms of the middle FM layer (e.g., 310B). This is compared to a reference SNR value of 18.8 decibels (dB). The STT effect is not considered here, and the magnetic noise comes only from thermal fluctuations of the magnetization at room temperature. Figure 5 In FIG. 3 , it can be seen that for the low Ms layer 310B, an SNR gain of about 1 db is achievable. The reduced STT in the layers 310B and 310C may further improve the SNR.

[0031] exist Figure 3A and Figure 3B In the reader type shown, the signal amplitude increased by 6% and the asymmetry increased by 3% compared to the reference reader with a bulk free layer. Figure 3A and Figure 3B The cross-track resolution in a reader of the type shown remains unchanged relative to the cross-track resolution of a reference reader having a bulk free layer.

[0032] Other parameters that may be varied for optimal reader performance include the thickness of layers 310A-310C, the Ms of layer 310A and layer 310B, the strength of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling via the spacer layers 312A and 312B in the synthetic ferromagnetic free layer 310, and the bias field defined by the side shield 322 and the Ms of the side shield 322-free layer gap.

[0033] As described above, the synthetic ferromagnetic free layer may include more than three layers, and the structural layers of the multi-layer free layer may have different Ms values. In some embodiments, the (multiple) constituent layers whose magnetization is set by the bias field of the side shield may have an Ms greater than approximately 1 Tesla (T). In such embodiments, CoFe alloys with different compositions may be used for these layers. In addition, in such embodiments, the (multiple) layers whose magnetization is oriented relative to the bias field of the side shield may have an Ms that does not exceed 1T. CoFeX alloys may be used to adjust the magnetization intensity to a predetermined level, where X may be Ta, Zr, Hf or other doping elements, and where the composition of X may vary between 1-40%. NiFe alloys may also be used.

[0034] The description of the embodiments described herein is intended to provide a general understanding of the structure of each embodiment. The description is not intended to be a complete description of all elements and features of the devices and systems that utilize the structures or methods described herein. Many other embodiments will be apparent to those skilled in the art after reviewing the present invention. Other embodiments may also be utilized and derived from the present disclosure so that structural and logical substitutions and changes may be made without departing from the scope of the present disclosure. Additionally, these illustrations are merely representative and may be drawn to scale. Certain proportions in the illustrations may be enlarged, while other proportions may be reduced. Thus, the present disclosure and the accompanying drawings should be considered illustrative, not restrictive.

[0035] One or more embodiments of the present invention may be referred to herein, individually and / or collectively, by the term "invention", for convenience only, and are not intended to limit the scope of the present application to any particular invention or inventive concept. In addition, although specific embodiments have been shown and described herein, it should be appreciated that any subsequent arrangements designed to achieve the same or similar purposes may replace the specific embodiments shown. The present disclosure is intended to cover any subsequent modifications or variations of the various embodiments. Combinations of the above embodiments and other embodiments not specifically described herein will be apparent to those skilled in the art after reading the above description.

[0036] The Abstract of the present disclosure is provided to comply with 37 CFR § 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 combined together or described in a single embodiment for the purpose of linking the present disclosure together. The present invention should not be interpreted as reflecting the intention that the claimed embodiments adopt more features than those explicitly recited in each claim. On the contrary, as reflected in the claims below, the subject matter of the present invention may be directed to less than all of the features of any one of the disclosed embodiments.

[0037] The subject matter disclosed above is intended to be considered illustrative rather than restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true spirit and scope of the present disclosure. Therefore, to obtain the maximum extent allowed by law, the scope of the present disclosure will be determined by the broadest interpretation permitted by the appended claims and their equivalents, and shall not be restricted or limited by the above detailed description.

[0038] Further examples:

[0039] Example 1. A reader, comprising: a read sensor, comprising: a multi-layer synthetic ferromagnetic free layer, the multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

[0040] Example 2. The reader of Example 1, wherein the multi-layer synthetic ferromagnetic free layer comprises a three-layer synthetic ferromagnetic free layer.

[0041] Example 3. The reader of Example 2 further comprises a synthetic antiferromagnetic (SAF) structure below the three-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the SAF structure.

[0042] Example 4. A reader as described in Example 3, characterized in that the three-layer synthetic ferromagnetic free layer includes a bottom magnetic layer above the tunneling barrier layer, an intermediate magnetic layer above the bottom magnetic layer, and a top magnetic layer above 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.

[0043] Example 5. The reader of Example 4, further comprising at least one side shield providing a bias magnetic field in the first direction.

[0044] Example 6. The reader of Example 5, wherein the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer have a magnetization orientation in the first direction set by the at least one side shield.

[0045] Example 7. The reader of Example 6, wherein the middle magnetic layer of the three-layer synthetic ferromagnetic free layer includes a magnetization orientation in a second direction that is opposite to the bias magnetic field in the first direction.

[0046] Example 8. A reader as described in Example 4, characterized in that the spontaneous magnetization of the material of the middle magnetic layer of the three-layer synthetic ferromagnetic free layer is lower than the spontaneous magnetization of the material of the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer, and lower than the spontaneous magnetization of the top magnetic layer of the three-layer synthetic ferromagnetic free layer.

[0047] Example 9. A method of forming a reader, comprising: forming a read sensor by: forming a multi-layer synthetic ferromagnetic free layer, the multi-layer synthetic ferromagnetic free layer having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

[0048] Example 10. The method of Example 9, wherein forming the multi-layer synthetic ferromagnetic free layer includes forming a three-layer synthetic ferromagnetic free layer.

[0049] Example 11. The method of Example 10 further includes forming a synthetic antiferromagnetic (SAF) structure below the three-layer synthetic ferromagnetic free layer, and forming a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the SAF structure.

[0050] Example 12. The method as described in Example 11 is characterized in that forming the three-layer synthetic ferromagnetic free layer includes forming a bottom magnetic layer above the tunneling barrier layer, forming a first spacer layer above the bottom magnetic layer, forming an intermediate magnetic layer above the first spacer layer, forming a second spacer layer above the intermediate magnetic layer, and forming a top magnetic layer above the second spacer layer.

[0051] Example 13. The method of Example 12, further comprising forming at least one side shield that provides a bias magnetic field in a first direction.

[0052] Example 14. The method of Example 13, further comprising setting the magnetization orientation of both the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer in the first direction by the at least one side shield.

[0053] Example 15. The method of Example 14 further comprises setting a magnetization orientation of the middle magnetic layer of the three-layer synthetic ferromagnetic free layer in a second direction, the magnetization orientation being opposite to the bias magnetic field in the first direction.

[0054] Example 16. A reader as in Example 12, further comprising forming the middle magnetic layer of the three-layer synthetic ferromagnetic free layer using a material having a spontaneous magnetization, wherein the spontaneous magnetization is lower than the spontaneous magnetization of the material used to form the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and lower than the spontaneous magnetization of the material used to form the top magnetic layer of the three-layer synthetic ferromagnetic free layer.

[0055] Example 17. An apparatus comprising: a read sensor including 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 three-layer synthetic ferromagnetic free layer.

[0056] Example 18. The device of Example 17 further comprises a synthetic antiferromagnetic (SAF) structure below the three-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the SAF structure.

[0057] Example 19. A device as described in Example 18, characterized in that the three-layer synthetic ferromagnetic free layer includes a bottom magnetic layer above a tunneling barrier layer, an intermediate magnetic layer above the bottom magnetic layer, and a top magnetic layer above 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.

[0058] Example 20. An apparatus as described in Example 19, characterized in that: the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer have a magnetization orientation in the first direction set by the at least one side shield; and the middle magnetic layer of the three-layer synthetic ferromagnetic free layer includes a magnetization orientation in a second direction, and the magnetization orientation is opposite to the bias magnetic field in the first direction.

Claims

1. A reader, comprising: Read sensors, including: A multi-layer synthetic ferromagnetic free layer includes at least three magnetic layers and has a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

2. The reader according to claim 1, wherein: The multi-layer synthetic ferromagnetic free layer includes a three-layer synthetic ferromagnetic free layer, and the reader further includes a synthetic antiferromagnetic (SAF) structure below the three-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the synthetic antiferromagnetic (SAF) structure.

3. The reader according to claim 2, characterized in that The three-layer synthetic ferromagnetic free layer includes a bottom magnetic layer above the tunneling barrier layer, a middle magnetic layer above the bottom magnetic layer, and a top magnetic layer above the middle magnetic layer, and wherein the bottom magnetic layer and the middle magnetic layer are separated by a first spacer layer, and the middle magnetic layer and the top magnetic layer are separated by a second spacer layer. 4 . The reader of claim 3 , further comprising at least one side shield providing a bias magnetic field in a first direction.

5. The reader according to claim 4, characterized in that The bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer have a magnetization orientation in the first direction that is set by the at least one side shield.

6. The reader according to claim 5, characterized in that The middle magnetic layer of the tri-layer synthetic ferromagnetic free layer includes a magnetization orientation in a second direction that is opposite to the bias magnetic field in the first direction.

7. The reader of claim 3, wherein: The spontaneous magnetization of the material of the middle magnetic layer of the three-layer synthetic ferromagnetic free layer is lower than the spontaneous magnetization of the material of the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and lower than the spontaneous magnetization of the top magnetic layer of the three-layer synthetic ferromagnetic free layer.

8. A method of forming a reader, comprising: The reading sensor is formed in the following way: A multi-layer synthetic ferromagnetic free layer is formed, the multi-layer synthetic ferromagnetic free layer including at least three magnetic layers and having a non-zero net magnetization that biases the multi-layer synthetic ferromagnetic free layer.

9. The method according to claim 8, characterized in that The multilayer synthetic ferromagnetic free layer includes a three-layer synthetic ferromagnetic free layer, and the method further includes forming a synthetic antiferromagnetic (SAF) structure under the three-layer synthetic ferromagnetic free layer, and forming a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the synthetic antiferromagnetic (SAF) structure.

10. The method according to claim 9, characterized in that Forming the three-layer synthetic ferromagnetic free layer includes forming a bottom magnetic layer above the tunneling barrier layer, forming a first spacer layer above the bottom magnetic layer, forming a middle magnetic layer above the first spacer layer, forming a second spacer layer above the middle magnetic layer, and forming a top magnetic layer above the second spacer layer.

11. The method of claim 10, further comprising forming at least one side shield that provides a bias magnetic field in a first direction.

12. The method of claim 11, further comprising setting the magnetization orientation of both the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer in the first direction by the at least one side shield.

13. The method of claim 12, further comprising setting a magnetization orientation of the middle magnetic layer of the three-layer synthetic ferromagnetic free layer in a second direction that is opposite to the bias magnetic field in the first direction.

14. The reader of claim 10 , further comprising forming the middle magnetic layer of the three-layer synthetic ferromagnetic free layer using a material having a spontaneous magnetization lower than the spontaneous magnetization of the material used to form the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and lower than the spontaneous magnetization of the material used to form the top magnetic layer of the three-layer synthetic ferromagnetic free layer.

15. An apparatus comprising: a read sensor comprising a three-layer synthetic ferromagnetic free layer; as well as At least one side shield provides a bias magnetic field in a first direction to bias the three-layer synthetic ferromagnetic free layer.

16. The apparatus of claim 15, further comprising a synthetic antiferromagnetic (SAF) structure below the three-layer synthetic ferromagnetic free layer, and a tunneling barrier layer between the three-layer synthetic ferromagnetic free layer and the synthetic antiferromagnetic (SAF) structure.

17. The device according to claim 16, characterized in that The three-layer synthetic ferromagnetic free layer includes a bottom magnetic layer above a tunneling barrier layer, a middle magnetic layer above the bottom magnetic layer, and a top magnetic layer above the middle magnetic layer, and wherein the bottom magnetic layer and the middle magnetic layer are separated by a first spacer layer, and the middle magnetic layer and the top magnetic layer are separated by a second spacer layer.

18. The device according to claim 17, characterized in that: the bottom magnetic layer of the three-layer synthetic ferromagnetic free layer and the top magnetic layer of the three-layer synthetic ferromagnetic free layer have a magnetization orientation in the first direction set by the at least one side shield; and The middle magnetic layer of the three-layer synthetic ferromagnetic free layer includes a magnetization orientation in a second direction, The magnetization orientation is opposite to the bias magnetic field in the first direction.

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