Patent Publication Number: US-11657836-B2

Title: Magnetic recording devices having negative polarization layer to enhance spin-transfer torque

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 16/912,509, filed Jun. 25, 2020, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     Aspects of the present disclosure generally relate to a magnetic recording head of a spintronic device, such as a write head of a data storage device, for example a magnetic media drive. 
     Description of the Related Art 
     The heart of the functioning and capability of a computer is the storing and writing of data to a data storage device, such as a hard disk drive (HDD). The volume of data processed by a computer is increasing rapidly. There is a need for higher recording density of a magnetic recording medium to increase the function and the capability of a computer. 
     In order to achieve higher recording densities, such as recording densities exceeding 2 Tbit/in 2  for a magnetic recording medium, the width and pitch of write tracks are narrowed, and thus the corresponding magnetically recorded bits encoded in each write track is narrowed. One challenge in narrowing the width and pitch of write tracks is decreasing a surface area of a main pole of the magnetic write head at a media facing surface. As the main pole becomes smaller, the writing field becomes smaller as well, limiting the effectiveness of the magnetic write head. 
     Heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) are two types of energy-assisted recording technology to improve the recording density of a magnetic recording medium, such as a HDD. In MAMR, a spin torque oscillator (STO) device is located next to or near the write element in order to produce a high-frequency AC field, such as in a microwave frequency band. The high-frequency AC field reduces an effective coercivity of a magnetic recording medium used to store data and allows writing of the magnetic recording medium at lower magnetic writing fields emanated from the write pole. Thus, higher recording density of the magnetic recording medium may be achieved by MAMR technology. 
     Energy-assisted recording write heads may require an undesirable high voltage and/or an undesirable high current to produce a write field enhancement. A high voltage and/or high current may impact the lifetime and the reliability of the write head by degrading components of the write head. Lowering the voltage, moment-thickness product of the energy-assist magnetic layer, or the current can hinder writer performance, lower areal density capability (ADC), and/or limit the materials used in write heads. 
     Therefore, there is a need for write heads that simply and effectively facilitate write head performance reliability and high moment-thickness product of the energy-assist magnetic layer while facilitating lower voltage or current to facilitate effective and efficient magnetic recording, and high ADC of magnetic recording. 
     SUMMARY OF THE DISCLOSURE 
     Aspects of the present disclosure generally relate to a magnetic recording head of a spintronic device, such as a write head of a data storage device, for example a magnetic media drive. In one example, a magnetic recording head includes a main pole, a trailing shield, and a spin torque layer (STL) between the main pole and the trailing shield that provides energy-assisted write field enhancement. The magnetic recording head includes a first layer structure on the main pole, and the first layer structure includes a negative polarization layer. The magnetic recording head also includes a second layer structure disposed on the negative polarization layer and between the negative polarization layer and the STL. The negative polarization layer is an FeCr layer. The second layer structure includes a Cr layer disposed on the FeCr layer, and a Cu layer disposed on the Cr layer and between the Cr layer and the STL. 
     In one implementation, a magnetic recording head includes a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and a first spacer layer between the STL and the trailing shield. The magnetic recording head also includes a multilayer structure disposed on the main pole and between the main pole and the STL. The multilayer structure includes a first layer structure on the main pole. The first layer structure includes a negative polarization layer. The multilayer structure also includes a second layer structure disposed on the negative polarization layer and between the negative polarization layer and the STL. 
     In one implementation, a magnetic recording head includes a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and a multilayer structure disposed on the main pole and between the main pole and the STL. The multilayer structure includes an FeCr layer between the main pole and the STL, a Cr layer disposed on the FeCr layer, and a Cu layer disposed on the Cr layer and between the Cr layer and the STL. 
     In one implementation, a magnetic recording head includes a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and at least one negative polarization layer between the main pole and the STL. The at least one negative polarization layer includes a magnetic material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    is a schematic illustration of a magnetic recording device, according to one implementation. 
         FIG.  2    is a schematic illustration of a cross sectional side view of a head assembly facing the magnetic disk shown in  FIG.  1    or other magnetic storage medium, according to one implementation. 
         FIG.  3 A  is a schematic illustration of a plan view of an MFS of the write head shown in  FIG.  2   , according to one implementation. 
         FIG.  3 B  is a schematic illustration of a plan view of an MFS of the write head shown in  FIG.  2   , according to one implementation. 
         FIG.  4    is a schematic illustration of a cross-sectional throat view of the spintronic device of the write head shown in  FIG.  3 A , according to one implementation. 
         FIG.  5    is a schematic graphical illustration of calculated torque of an STL versus an angle of magnetization for the STL, according to one implementation. 
         FIG.  6    is a schematic graphical illustration of an angle of magnetization for the STL versus applied current density, according to one implementation. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     Aspects of the present disclosure generally relate to a magnetic recording head of a spintronic device, such as a write head of a data storage device, for example a magnetic media drive. In one example, a magnetic recording head includes a main pole, a trailing shield, and a spin torque layer (STL) between the main pole and the trailing shield. The magnetic recording head includes a first layer structure on the main pole, and the first layer structure includes a negative polarization layer. The magnetic recording head also includes a second layer structure disposed on the negative polarization layer and between the negative polarization layer and the STL. The negative polarization layer is an FeCr layer. The second layer structure includes a Cr layer disposed on the FeCr layer, and a Cu layer disposed on the Cr layer and between the Cr layer and the STL. 
       FIG.  1    is a schematic illustration of a magnetic recording device  100 , according to one implementation. The magnetic recording device  100  includes a magnetic recording head, such as a write head. The magnetic recording device  100  is a magnetic media drive, such as a hard disk drive (HDD). Such magnetic media drives may be a single drive/device or include multiple drives/devices. For the ease of illustration, a single disk drive is shown as the magnetic recording device  100  in the implementation illustrated in  FIG.  1   . The magnet recording device  100  (e.g., a disk drive) includes at least one rotatable magnetic disk  112  supported on a spindle  114  and rotated by a drive motor  118 . The magnetic recording on each rotatable magnetic disk  112  is in the form of any suitable patterns of data tracks, such as annular patterns of concentric data tracks on the rotatable magnetic disk  112 . 
     At least one slider  113  is positioned near the rotatable magnetic disk  112 . Each slider  113  supports a head assembly  121 . The head assembly  121  includes one or more magnetic recording heads (such as read/write heads), such as a write head including a spintronic device. As the rotatable magnetic disk  112  rotates, the slider  113  moves radially in and out over the disk surface  122  so that the head assembly  121  may access different tracks of the rotatable magnetic disk  112  where desired data are written. Each slider  113  is attached to an actuator arm  119  by way of a suspension  115 . The suspension  115  provides a slight spring force which biases the slider  113  toward the disk surface  122 . Each actuator arm  119  is attached to an actuator  127 . The actuator  127  as shown in  FIG.  1    may be a voice coil motor (VCM). The VCM includes a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by a control unit  129 . 
     The head assembly  121 , such as a write head of the head assembly  121 , includes a media facing surface (MFS) such as an air bearing surface (ABS) that faces the disk surface  122 . During operation of the magnetic recording device  100 , the rotation of the rotatable magnetic disk  112  generates an air or gas bearing between the slider  113  and the disk surface  122  which exerts an upward force or lift on the slider  113 . The air or gas bearing thus counter-balances the slight spring force of suspension  115  and supports the slider  113  off and slightly above the disk surface  122  by a small, substantially constant spacing during operation. 
     The various components of the magnetic recording device  100  are controlled in operation by control signals generated by control unit  129 , such as access control signals and internal clock signals. The control unit  129  includes logic control circuits, storage means and a microprocessor. The control unit  129  generates control signals to control various system operations such as drive motor control signals on a line  123  and head position and seek control signals on a line  128 . The control signals on line  128  provide the desired current profiles to optimally move and position slider  113  to the desired data track on rotatable magnetic disk  112 . Write and read signals are communicated to and from the head assembly  121  by way of recording channel  125 . In one embodiment, which can be combined with other embodiments, the magnetic recording device  100  may further include a plurality of media, or disks, a plurality of actuators, and/or a plurality number of sliders. 
       FIG.  2    is a schematic illustration of a cross sectional side view of a head assembly  200  facing the rotatable magnetic disk  112  shown in  FIG.  1    or other magnetic storage medium, according to one implementation. The head assembly  200  may correspond to the head assembly  121  described in  FIG.  1   . The head assembly  200  includes a media facing surface (MFS)  212 , such as an air bearing surface (ABS), facing the rotatable magnetic disk  112 . As shown in  FIG.  2   , the rotatable magnetic disk  112  relatively moves in the direction indicated by the arrow  232  and the head assembly  200  relatively moves in the direction indicated by the arrow  233 . 
     In one embodiment, which can be combined with other embodiments, the head assembly  200  includes a magnetic read head  211 . The magnetic read head  211  may include a sensing element  204  disposed between shields S 1  and S 2 . The sensing element  204  is a magnetoresistive (MR) sensing element, such an element exerting a tunneling magneto-resistive (TMR) effect, a magneto-resistance (GMR) effect, an extraordinary magneto-Resistive (EMR) effect, or a spin torque oscillator (STO) effect. The magnetic fields of magnetized regions in the rotatable magnetic disk  112 , such as perpendicular recorded bits or longitudinal recorded bits, are detectable by the sensing element  204  as the recorded bits. 
     The head assembly  200  includes a write head  210 . In one embodiment, which can be combined with other embodiments, the write head  210  includes a main pole  220 , a leading shield  206 , a trailing shield (TS)  240 , and a spintronic device  230  disposed between the main pole  220  and the TS  240 . The main pole  220  serves as a first electrode. Each of the main pole  220 , the spintronic device  230 , the leading shield  206 , and the trailing shield (TS)  240  has a front portion at the MFS. 
     The main pole  220  includes a magnetic material, such as CoFe, CoFeNi, or FeNi, other suitable magnetic materials. In one embodiment, which can be combined with other embodiments, the main pole  220  includes small grains of magnetic materials in a random texture, such as body-centered cubic (BCC) materials formed in a random texture. In one example, a random texture of the main pole  220  is formed by electrodeposition. The write head  210  includes a coil  218  around the main pole  220  that excites the main pole  220  to produce a writing magnetic field for affecting a magnetic recording medium of the rotatable magnetic disk  112 . The coil  218  may be a helical structure or one or more sets of pancake structures. 
     In one embodiment, which can be combined with other embodiments, the main pole  220  includes a trailing taper  242  and a leading taper  244 . The trailing taper  242  extends from a location recessed from the MFS  212  to the MFS  212 . The leading taper  244  extends from a location recessed from the MFS  212  to the MFS  212 . The trailing taper  242  and the leading taper  244  may have the same degree or different degree of taper with respect to a longitudinal axis  260  of the main pole  220 . In one embodiment, which can be combined with other embodiments, the main pole  220  does not include the trailing taper  242  and the leading taper  244 . In such an embodiment, the main pole  220  includes a trailing side and a leading side in which the trailing side and the leading side are substantially parallel. 
     The TS  240  includes a magnetic material, such as FeNi, or other suitable magnetic materials, serving as a second electrode and return pole for the main pole  220 . The leading shield  206  may provide electromagnetic shielding and is separated from the main pole  220  by a leading gap  254 . 
     The spintronic device  230  is positioned proximate the main pole  220  and reduces the coercive force of the magnetic recording medium, so that smaller writing fields can be used to record data. An electron current is applied to spintronic device  230  from a current source  270  to produce a microwave field. The electron current may include direct current (DC) waveforms, pulsed DC waveforms, and/or pulsed current waveforms going to positive and negative voltages, or other suitable waveforms. 
     In one embodiment, which can be combined with other embodiments, the spintronic device  230  is electrically coupled to the main pole  220  and the TS  240 . The main pole  220  and the TS  240  are separated in an area by an insulating layer  272 . The current source  270  may provide electron current to the spintronic device  230  through the main pole  220  and the TS  240 . For direct current or pulsed current, the current source  270  may flow electron current from the main pole  220  through the spintronic device  230  to the TS  240  or may flow electron current from the TS  240  through the spintronic device  230  to the main pole  220  depending on the orientation of the spintronic device  230 . In one embodiment, which can be combined with other embodiments, the spintronic device  230  is coupled to electrical leads providing an electron current other than from the main pole  220  and/or the TS  240 . 
       FIG.  3 A  is a schematic illustration of a plan view of an MFS of the write head  210  shown in  FIG.  2   , according to one implementation. The write head  210  includes a spintronic device  330  between the main pole  220  and the TS  240  in the track direction. The spintronic device  330  may be used as the spintronic device  230  shown in  FIG.  2   . 
     It is to be understood that the magnetic recording head discussed herein is applicable to a data storage device such as a hard disk drive (HDD) as well as a tape drive such as a tape embedded drive (TED) or an insertable tape media drive. An example TED is described in co-pending patent application titled “Tape Embedded Drive,” U.S. application Ser. No. 16/365,034, filed Mar. 31, 2019, assigned to the same assignee of this application, which is herein incorporated by reference. As such, any reference in the detailed description to a HDD or tape drive is merely for exemplification purposes and is not intended to limit the disclosure unless explicitly claimed. Furthermore, reference to or claims directed to magnetic recording devices are intended to include both HDD and tape drive unless HDD or tape drive devices are explicitly claimed. 
     It is also to be understood that aspects disclosed herein, such as the magnetic recording heads, may be used in magnetic sensor applications outside of HDD&#39;s and tape media drives such as TED&#39;s, such as spintronic devices other than HDD&#39;s and tape media drives. As an example, aspects disclosed herein may be used in magnetic elements in magnetoresistive random-access memory (MRAM) devices (e.g., magnetic tunnel junctions as part of memory elements), magnetic sensors or other spintronic devices. 
     The spintronic device  330  uses spin-transfer torque (STT) to facilitate magnetic recording. The present disclosure contemplates that the spintronic device  330  may be used with spin-orbital torque (SOT). 
     The spintronic device  330  includes a multilayer structure  310  disposed on the main pole  220 , a spin torque layer  320  (STL), and a first spacer layer  390 . In one embodiment, which can be combined with other embodiments, the STL  320  is a spin polarization layer (SPL) or a spin polarizing layer. The sides of the spintronic device  330  at the MFS are ion milled or patterned, for example, to form the spintronic device shape as shown. The multilayer structure  310  is disposed between and in contact with the main pole  220  and the STL  320 . The multilayer structure  310  is between the main pole  220  and the trailing shield  240 . The multilayer structure  310  is used in place of a seed layer disposed on the main pole  220 . The first spacer layer  390  is between the STL  320  and the trailing shield  240 . A TS hot seed layer  380  is over the first spacer layer  390 . The TS hot seed layer  380  is magnetically stitched with a notch of the TS  240 . 
     A current source  270  is configured to supply a current to the spintronic device  330 . The current supplied using the current source  270  facilitates an electron flow from the main pole  220  through the spintronic device  330  to the TS  240 . The direction of the current supplied through the spintronic device  330  is opposite of the direction of the electron flow through the spintronic device  330 . Polarized electrons from the STL  320  are reflected off from a first interface  301  between the TS  240  and the first spacer layer  390 , such as between the TS hot seed layer  380  and the first spacer layer  390 , back toward the STL  320 . Spin accumulation and spin torque occurs at a second interface  302  between the first spacer layer  390  and the STL  320 . 
     The STL  320  is initially magnetized in the same direction as magnetization of the main pole  220  and the TS  240 , which is in a direction from the main pole  220  to the TS  240  and is in the same direction as the electron flow. The spin torque acts on the STL  320  causing spin flipping of the STL  320  and precession of magnetization M of the STL  320 . Precession of the magnetization M of the STL  320  can generate an assisting magnetic field, such as a DC field, emitted to a magnetic recording medium. The assisting magnetic field reduces the coercive force of the recording medium and enhances the write field from the main pole  220  to write to the recording medium. 
     The bias voltage (Vjump) at which spin flipping occurs is estimated according to formula (1): 
                   Vjump   =       J   c     *   RA             (   1   )               
in which J c  is the critical current density for STT switching against the gap field.
 
     The multilayer structure  310  includes a first layer structure  311  on the main pole  220  and a second layer structure  314  on the first layer structure  311 . The spintronic device includes at least one negative polarization layer (NPL)  312 . The second layer structure  314  is between the first layer structure  311  and the STL  320 , and is in contact with the first layer structure  311  and the STL  320 . The first layer structure  311  includes the negative polarization layer (NPL)  312 . The negative polarization layer  312  is magnetic and includes a magnetic material, and is magnetized in the same direction as the main pole  220  and the electron flow. In one embodiment, which can be combined with other embodiments, the first layer structure  311  is a monolayer including the negative polarization layer  312  where the negative polarization layer  312  is in contact with the main pole  220  and the second layer structure  314 , and is magnetically stitched to the main pole  220 . In one example, the negative polarization layer  312  is magnetically stitched to the main pole  220 . A notch in the main pole  220  can be created during the formation process of the spintronic device  330 . In one embodiment, which can be combined with other embodiments, the first layer structure  311  is a bilayer and a ferromagnetic layer  313  is disposed between the main pole  220  and the negative polarization layer  312 . 
     In one embodiment, which can be combined with other embodiments, the negative polarization layer  312  includes a plurality of electron energy bands that includes a majority spin channel and a minority spin channel. For the negative polarization layer  312 , the minority spin channel includes a conductivity that is larger than a conductivity of the majority spin channel. 
     In one embodiment, which can be combined with other embodiments, the ferromagnetic layer  313  includes a plurality of electron energy bands that includes a majority spin channel and a minority spin channel. For the ferromagnetic layer  313 , the majority spin channel includes a conductivity that is larger than a conductivity of the minority spin channel. 
     The NPL  312  includes one or more of Fe, Cr, N, Co, and/or Gd, such as FeCr, or an iron nitride (Fe x N x ). In one embodiment, which can be combined with other embodiments, the NPL  312  includes one or more ferromagnetic materials that have a negative spin accumulation. In one embodiment, which can be combined with other embodiments, the NPL  312  includes an alloy of two materials with lattices that are oppositely aligned, such as Co and Gd in an antiparallel alignment. The first layer structure  311  includes a first thickness T1. The first thickness T1 is within a range of 3 nm to 10 nm. The first thickness T1 may be varied according to a diffusion length of the NPL  312 . In one example, the NPL  312  includes a spin diffusion length of about 2 nm. The NPL  312  includes a thickness T3 that is within a range of 3 nm to 6 nm, such as 5 nm. In one example, such as an example where the first layer structure  311  is a monolayer, the first thickness T1 of the first layer structure  311  is equal to the thickness T3 of the NPL  312 . The ferromagnetic layer  313 , if included, includes a thickness T4 that is up to 6 nm. 
     The second layer structure  314  includes a material that has a long diffusion length, such as a diffusion length that is longer than the diffusion length of the NPL  312 . The second layer structure  314  includes one or more layers each including one or more of Cr or Cu. The second layer structure  314  is a composite structure including at least two differing materials. In one embodiment, which can be combined with other embodiments, the second layer structure  314  is a monolayer including one or more of Cr or Cu. In one embodiment, which can be combined with other embodiments, the second layer structure  314  is a bilayer and includes a first layer  315  disposed on the NPL  312 , and a second layer  316  disposed on the first layer  315  and between the first layer  315  and the STL  320 . The first layer  315  and the second layer  316  each includes one or more of Cr or Cu. The first layer  315  includes Cr and the second layer  316  includes Cu. The first layer  315  includes a material having a negative interface polarization factor ( ), such as about −0.2. The negative interface polarization factor ( ) is at the interface between the first layer  315  and the NPL  312 . The second layer structure  315  includes a second thickness T2 that is within a range of 3 nm to 8 nm. The first layer  315  includes a thickness T5 that is within a range of 0.5 nm to 1.5 nm, such as 1.0 nm. The second layer  316  includes a thickness T6 that is within a range of 1.5 nm to 7.5 nm, such as within a range of 1.5 nm to 2.5 nm, for example 2.0 nm. The second layer structure  314  is a spacer layer structure that is a second spacer layer if the first spacer layer  390  is included. In one example, such as when the second layer structure is a bilayer, the second thickness T2 is equal to the thickness T5 added with the thickness T6. 
     In one embodiment, which can be combined with other embodiments, the first layer structure  311  is a monolayer including the NPL  312  where the NPL  312  is an FeCr layer having the first thickness T1, the second layer structure  314  is a bilayer including the first layer  315  and the second layer  316 , the first layer  315  is a Cr layer having the thickness T5, and the second layer  316  is a Cu layer having the thickness T6. 
       FIG.  3 B  is a schematic illustration of a plan view of an MFS of the write head  210  shown in  FIG.  2   , according to one implementation. The write head  210  includes a spintronic device  395  between the main pole  220  and the TS  240  in the track direction. The spintronic device  395  may be used as the spintronic device  230  shown in  FIG.  2   . 
     The spintronic device  395  is similar to the spintronic device  330  shown in  FIG.  3 A , and includes one or more of the aspects, features, components, and/or properties thereof. The spintronic device  395  includes a multilayer structure  394  that is similar to the multilayer structure  310  shown in  FIG.  3 A . In the spintronic device  395 , the dispositions of the multilayer structure  394  and the first spacer layer  390  are switched relative to the dispositions of the multilayer structure  310  and the first spacer layer  390  shown in  FIG.  3 A . In the spintronic device  395  shown in the implementation of  FIG.  3 B , the first spacer layer  390  is formed between the STL  320  and the main pole  220 , and the multilayer structure  394  is formed between the STL  320  and the TS hot seed layer  380 . In the multilayer structure  394  of the spintronic device  395 , dispositions of the layers  312 ,  313 ,  315 ,  316  are reversed relative to the dispositions of the layers  312 ,  313 ,  315 ,  316  shown in the spintronic device  330  of  FIG.  3 A . The dispositions of the layers  312 ,  313 ,  315 ,  316  are such that the ferromagnetic layer  313  is disposed at a first end of the multilayer structure  394  and in contact with the TS hot seed layer  380 , and such that the second layer  316  is disposed at a second end of the multilayer structure  394  and in contact with the STL  320 . 
     In the implementation shown in  FIG.  3 B , the directions of the current through the spintronic device  395  and the electron flow through the spintronic device  395  are reversed relative to the directions of the current and the electron flow shown in  FIG.  3 A . The current flowing through the spintronic device  395  flows from the main pole  220  and to the TS  240 . The electron flow flowing through the spintronic device  395  flows from the TS  240  and to the main pole  220 . The direction of the current supplied using the current source  270  through the spintronic device  395  is opposite of the direction of the electron flow through the spintronic device  395 . 
     Polarized electrons from the STL  320  are reflected off from a first interface  301  between the main pole  220  and the first spacer layer  390 , and back toward the STL  320 . Spin accumulation and spin torque occurs at a second interface  302  between the first spacer layer  390  and the STL  320 . 
     The magnetizations of the main pole  220 , the NPL  312 , the STL  320 , and the TS  240  in the spintronic device  395  shown in  FIG.  3 B  are in the same directions as the magnetizations of the main pole  220 , the NPL  312 , the STL  320 , and the TS  240  shown in and described in relation to the spintronic device  330  of  FIG.  3 A . The present disclosure contemplates that, depending on a polarity of the write current through a write coil (such as the coil  218  shown in  FIG.  2   ), the magnetizations of magnetic layers (such as the main pole  220 , the NPL  312 , the STL  320 , and the TS  240 ) may be in a direction from the main pole  220  and toward the TS  240  (as shown in  FIG.  3 A  and  FIG.  3 B ) or may be in a direction from the TS  240  and toward the main pole  220 . 
       FIG.  4    is a schematic illustration of a cross-sectional throat view of the spintronic device  330  of the write head  210  shown in  FIG.  3 A , according to one implementation. The layers  310 ,  320 ,  330 , the main pole  220 , and the TS  240  can have the same cross-track widths (as shown in  FIG.  3 A ) or may have differing cross-track widths. The layers  310 ,  320 ,  330 , may have differing stripe heights (as shown in  FIG.  4   ), or may have the same stripe heights. The layers  310 ,  320 ,  330 , such as the first layer structure  311  and the second layer structure  314 , and the first spacer layer  390 , may be tapered (as shown in  FIG.  4   ) or non-tapered. 
     The STL  320  of the spintronic device  330 ,  395  of  FIGS.  3 A-B  and  4  may include one or more of NiFe, CoFe, CoFeNi, CoMnGe, NiCo, NiFeCu, CoFeMnGe, CoMnSi, CoFeSi, and/or other soft or hard ferromagnetic materials, other Heusler alloys, other suitable magnetic layers, and/or multiple layers thereof. The STL  320  can include a material having magnetic anisotropy oriented in any general direction, such as perpendicular, angled, or longitudinal, to the plane of the MFS. In one embodiment, which can be combined with other embodiments, the STL  320  includes a magnetic anisotropy initially oriented in the same direction as the magnetic orientation of the main pole  220  and the electron flow, as shown in  FIG.  3 A . 
     The first spacer layer  390  of the spintronic device  330 ,  395  shown in  FIGS.  3 A-B  and  4  includes one or more non-magnetic conductive materials, such as Au, Ag, Al, Cu, AgSn, NiAl, and/or other non-magnetic conductive materials, alloys thereof, and/or multiple layers thereof. The first spacer layer  390  may be made of a material having a high spin transmissivity for spin torque transfer on the STL  320 . 
     The second layer structure  314  is a non-magnetic spacer layer including one or more non-magnetic materials. The first and second layers  315 ,  316  of the second layer structure  314  include one or more non-magnetic conductive materials, such as Au, Ag, Al, Cu, AgSn, NiAl, Cr, and/or other non-magnetic conductive materials, alloys thereof, and/or multiple layers thereof. The first and second layers  315 ,  316  may be made of a material having a high spin transmissivity for spin torque transfer on the STL  320 . 
     The main pole  220  of the write head  210  shown in  FIGS.  3 A-B  and  4  may be any suitable shape (e.g., trapezoidal, triangular, etc.) having suitable dimensions. The write head  210  of  FIGS.  3 A-B  and  4  may include a leading shield positioned on one or more sides of the main pole  220  with a leading gap therebetween. The write head  210  of  FIGS.  3 A-B  and  4  may include a side gap positioned on the sides of the spintronic device  330 ,  395 . The side gap may include an insulating material. 
     In  FIG.  3 A  the track direction is labeled as the x-coordinate and the cross-track direction is labeled as the y-coordinate. The perpendicular direction to the MFS would be the z-coordinate into/out of the X-Y plane. In  FIG.  4   , the track direction is labeled as the x-coordinate and the general stripe height direction is labeled in the z-coordinate. 
     The multilayer structure  310  facilitates operation of the STL  320 . As an example, negative spin accumulation of the NPL  312  facilitates generating direct torque on the STL  320  to facilitate spin flipping of the STL  320  against the field direction, and to facilitate precession of the magnetization of the STL  320 . The NPL  312  facilitates applying torque to the STL  320  from both sides of the STL  320 , such as both in a direction from the TS  240  and to the STL  320 , and in a direction from the main pole  220  and to the STL  320 . As an example, the negative interface polarization factor ( ) of the second layer structure  314  enhances the negative spin polarization of the NPL  312 . Such aspects facilitate lower voltage or lower current for the spintronic device  330 ,  395  to facilitate reliability and effective performance of the write head  210  while facilitating high moment-thickness product and high ADC of magnetic recording for the write head  210 . Such aspects also facilitate modularity for various configurations of the write head  210  and the materials that may be used for various components of the write head  210 , which may further lower current density and/or voltage of the write head  210 . 
     Aspects of the multilayer structure  310  facilitate a reduction in critical current for flipping or switching of the STL  320  that is up to 30% relative to a seed layer on the main pole  220 , such as a reduction in critical current density J c  of up to 15%-20%, due to the increase in spin-transfer torque of the STL  320 . 
       FIG.  5    is a schematic graphical illustration of calculated torque of an STL versus an angle of magnetization for the STL, according to one implementation. The torque of the STL (normalized to critical current density J c ) is mapped on the vertical axis and the angle of magnetization θ is mapped on the horizontal axis. The torque versus the angle of magnetization θ is calculated using a Valet-Fert Transport Model. A first case  501  represents a seed layer on a main pole, and a second case  503  represents use of the NPL described herein. An increase profile  505  represents the increase of torque using the second case  503  relative to the first case  501 . As shown in  FIG.  5   , use of the NPL in the second case  503  results in an increase of torque of the STL that is up to 20% over the seed layer used in the first case  501 , across angles of magnetization θ. 
       FIG.  6    is a schematic graphical illustration of an angle of magnetization for the STL versus applied current density, according to one implementation. The angle of magnetization θ for the STL is mapped on the vertical axis and the applied current density J is mapped on the horizontal axis. The angle of magnetization θ versus the applied current density J is calculated using a Valet-Fert Transport Model. Critical current density J c  is for STL switching and corresponds to the point where the applied current density J is sufficient to rotate the magnetization of the STL from an initial orientation to switch or flip the magnetization of the STL to an opposite direction that is opposite of the initial orientation. A first case  601  represents a seed layer on a main pole, and a second case  603  represents use of the NPL described herein. As shown in  FIG.  6   , use of the NPL in the second case  603  results in a reduction  605  in applied current density J that is up to 30%-45% less than the applied current density of the first case  601 , across angles of magnetization θ. Also shown in  FIG.  6   , a critical current density Jc2 of the second case  603  is up to 30%-45% less than a critical current density Jc1 of the first case  601 . 
     Benefits of the present disclosure include simple and effective facilitated magnetic recording performance and reliability; increased ADC for magnetic recording; reduced voltage or current while maintaining or facilitating increased moment-thickness product, magnetic recording head performance and reliability; modularity in magnetic recording head materials; and modularity in magnetic recording device design configurations. 
     It is contemplated that one or more aspects disclosed herein may be combined. Moreover, it is contemplated that one or more aspects disclosed herein may include some or all of the aforementioned benefits. 
     In one embodiment, a magnetic recording head comprises a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and a first spacer layer between the STL and the trailing shield. The magnetic recording head also includes a multilayer structure disposed on the main pole and between the main pole and the STL. The multilayer structure includes a first layer structure on the main pole. The first layer structure includes a negative polarization layer. The multilayer structure also includes a second layer structure disposed on the negative polarization layer and between the negative polarization layer and the STL. The negative polarization layer is in contact with the main pole and the second layer structure is in contact with the STL. The negative polarization layer includes one or more of Fe, Cr, N, Co, or Gd. The negative polarization layer includes a ferromagnetic material, and the second layer structure includes a non-magnetic material. The negative polarization layer is an FeCr layer. The second layer structure includes a Cr layer on the negative polarization layer, and a Cu layer disposed on the Cr layer and between the Cr layer and the STL. The first layer structure also includes a ferromagnetic layer on the main pole and between the main pole and the negative polarization layer. The first layer structure includes a first thickness that is within a range of 3 nm to 10 nm. The second layer structure includes a second thickness that is within a range of 3 nm to 8 nm. The second layer structure includes a first layer disposed on the negative polarization layer of the first layer structure. The first layer of the second layer structure includes a material having a negative interface polarization factor. The second layer structure also includes a second layer disposed on the first layer and between the first layer and the STL. Each of the first layer and the second layer of the second layer structure includes one or more of Cr or Cu. The negative polarization layer is magnetically stitched to the main pole. A magnetic recording device including the magnetic recording head is also disclosed. 
     In one embodiment, a magnetic recording head comprises a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and a multilayer structure disposed on the main pole and between the main pole and the STL. The multilayer structure includes an FeCr layer between the main pole and the STL, a Cr layer disposed on the FeCr layer, and a Cu layer disposed on the Cr layer and between the Cr layer and the STL. The FeCr layer includes a thickness that is within a range of 3 nm to 6 nm. The Cr layer includes a thickness that is within a range of 0.5 nm to 1.5 nm, and the Cu layer includes a thickness that is within a range 1.5 nm to 7.5 nm. The thickness of the Cu layer is within a range of 1.5 nm to 2.5 nm. A magnetic recording device including the magnetic recording head is also disclosed. 
     In one embodiment, a magnetic recording head comprises a main pole, a trailing shield, a spin torque layer (STL) between the main pole and the trailing shield, and at least one negative polarization layer between the main pole and the STL. A magnetic recording device including the magnetic recording head is also disclosed. The at least one negative polarization layer includes a magnetic material. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.