Patent Publication Number: US-11657844-B1

Title: Heat-assisted magnetic recording head with a heat sink having a liner

Description:
TECHNICAL FIELD 
     The disclosure relates to a near-field transducer for a heat-assisted magnetic recording head of a hard disk drive. 
     BACKGROUND 
     Some hard disk drives (HDDs) utilize heat-assisted magnetic recording (HAMR) to increase the areal density of the HDD. A recording head of a HAMR HDD typically includes a laser, a near-field transducer (NFT) configured to briefly heat a small hot spot on a surface of a magnetic disk of the HDD, and a write pole configured to write data to the magnetic disk in the vicinity of the hot spot. The process of generating and condensing localized surface plasmons (LSPs) on the NFT to produce the hot spot generates enormous amounts of heat which may degrade and/or deform various components of the NFT, thus potentially reducing the performance and/or life expectancy of the HAMR head and the HDD. 
     SUMMARY 
     The present disclosure describes a heat-assisted magnetic recording (HAMR) head having a near-field transducer (NFT) that includes a near-field emitter and a more thermally stable middle disk. In some examples, the near-field emitter is a single, continuous feature that includes a peg disposed near a media-facing surface of the HAMR head and an anchor disk disposed behind the peg relative to the media-facing surface. The middle disk includes at least one thermally stable material. Providing a middle disk that includes a thermally stable material may, in some examples, reduce or prevent the occurrence of certain failure modes under thermal exposure (e.g., middle disk recession). A thermally stable middle disk may improve the reliability of HAMR heads. 
     The present disclosure also describes a HAMR head having a heat sink that includes a core and a liner that encloses the core. The liner includes a thermally stable material. In some examples, utilizing a heat sink with a liner of a thermally stable material reduces defects in the heat sink (e.g., reducing recession of the heat sink under thermal exposure). Providing a liner of a thermally stable material on a heat sink may, in some examples, improve the physical integrity of the heat sink and may enable the heat sink to dissipate heat away from features of the HAMR head (e.g., an NFT) more effectively and consistently over the lifetime of the HAMR head. 
     In one example, a heat-assisted magnetic recording head includes a near-field transducer including: a middle disk; and a near-field emitter including: a peg configured to produce a hot spot on a proximal magnetic disk, the peg disposed proximal to a media-facing surface of the heat-assisted magnetic recording head; and an anchor disk disposed behind the peg relative to the media-facing surface; and a heat sink including: a core including a primary metal; and a liner including a primary metal, wherein the liner is coupled to the core and is disposed along an outer surface of the core, wherein the middle disk is disposed between and coupled to the liner and the anchor disk, and wherein the primary metal of the liner comprises at least one of iridium, rhodium, tantalum, tungsten, or ruthenium. 
     These and other features and aspects of various examples may be understood in view of the following detailed discussion and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an example hard disk drive, in accordance with aspects of this disclosure. 
         FIG.  2    is a perspective view of an example slider, in accordance with aspects of this disclosure. 
         FIG.  3    is a cross-sectional view of an example HAMR head, in accordance with aspects of this disclosure. 
         FIG.  4    is a perspective view of an example HAMR head, in accordance with aspects of this disclosure. 
         FIG.  5    is a cross-sectional view of an example HAMR head, in accordance with aspects of this disclosure. 
         FIG.  6    is a perspective view of an example HAMR head, in accordance with aspects of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a perspective view of an example heat assisted magnetic recording (HAMR) hard disk drive (HDD), in accordance with aspects of this disclosure. HDD  100  includes a head stack assembly (HSA)  110  and one or more magnetic disks  108 . HSA  110  includes a plurality of head gimbal assemblies (HGA)  120 . Each HGA  120  includes a slider  122 . HSA  110  of  FIG.  1    includes a voice coil drive actuator  112 . Voice coil drive actuator  112  produces a magnetic field which exerts a force on an actuator mechanism  114 , causing actuator mechanism  114  to rotate about a shaft  116  in either rotational direction. Rotatable drive actuator arms  118  are mechanically coupled to actuator mechanism  114  and to each HGA  120  such that rotating actuator mechanism  114  causes rotatable drive actuator arms  118  and HGAs  120 , and thus sliders  122 , to move relative to magnetic disks  108 . 
       FIG.  2    is a perspective view of an example slider  222 , in accordance with aspects of this disclosure. Slider  222  is an example of slider  122  of  FIG.  1   . In the example of  FIG.  2   , slider  222  includes a slider body  224 , a laser  226 , a submount  228 , and a HAMR head  240 . 
     HAMR head  240  is configured to read data from and write data to a surface of a magnetic disk. HAMR head  240  includes a waveguide  230 , a near-field transducer (NFT)  250 , a writer  260 , and a reader  270 . In the example of  FIG.  2   , some features or parts of features of NFT  250 , writer  260 , and reader  270  are presented on a media-facing surface  205  that is positioned over a surface of a magnetic disk during some operations of the HDD (e.g., write operations, read operations). In some examples, media-facing surface  205  is an air-bearing surface (ABS) that is configured to maintain HAMR head  240  at a target spacing (e.g., a head-media spacing) from a surface of the magnetic disk during some operations of HDD  100 . During such operations, media-facing surface  205  faces and is held proximate to the moving surface of the magnetic disk by a cushion of gas, known as an active air bearing (AAB), that is produced from a dynamic flow of gas across a pattern of recessed sub-surfaces bound within the volume of slider body  224  by media-facing surface  205 . 
     Laser  226  is configured to emit photons of a target wavelength. In some examples, laser  226  emits photons with a wavelength in the near infrared range (e.g., approximately 830 nm) or visible range. Examples of laser  226  include an optically pumped semiconductor laser, a quantum well laser, an integrated laser, or other suitable laser. Laser  226  of this example may be configured as an edge emitting laser (EEL), vertical cavity surface emitting laser (VCSEL), or other type of laser. Other example HAMR heads may include other types of light sources such as light emitting diodes (LEDs) and surface emitting diodes. 
     In one example, laser  226  is coupled to slider body  224  via submount  228 . In the example of  FIG.  2   , laser  226  and submount  228  are located on a face of slider body  224  which is opposite to media-facing surface  205 . In some examples, laser  226  may be directly mounted to the slider body  224 . Submount  228  may be configured to redirect photons output from laser  226  so that the photons are directed into waveguide  230  in the negative y-direction of  FIG.  2    (e.g., toward NFT  250 ). The path between laser  226  and waveguide  230  may include one or more optical couplers, mode converters, and/or mode couplers. Waveguide  230  is formed integrally within slider body  224  and is configured to deliver photons from laser  226  to NFT  250 . While  FIG.  2    illustrates laser  226  coupled to slider body  224  via submount  228 , in some examples, laser  226  may be directly mounted to slider body  224 . 
     NFT  250  is configured to create a small hot spot on a magnetic disk. For example, NFT may generate and support a distribution of localized surface plasmons (LSPs) upon receiving incident photons from laser  226  by way of waveguide  230  and may condense the LSP distribution on an area or feature of NFT  250 . NFT  250  amplifies a near-field of the condensed LSP distribution and focuses the near-field toward a surface of a magnetic disk (e.g., a magnetic disk  108  of  FIG.  1   ) to produce a hot spot. Writer  260  is configured to generate a magnetic field from an electrical current and direct the magnetic field at the hot spot on the magnetic disk. The near-field energy heats and lowers the coercivity of the magnetic grains in the hot spot, thereby enabling these magnetic grains to be oriented by the magnetic field generated by writer  260 . Turning off laser  226  or moving NFT  250  toward a different location of the magnetic disk (or moving the magnetic disk such that NFT  250  faces a different location of the magnetic disk) removes the focused near-field energy from the hot spot. Removing the near-field energy allows the magnetic grains contained in the spot to cool. The cooling locks in the grain orientation induced by the magnetic field generated by writer  260 , thus preserving the bits of written data. 
       FIG.  3    is a cross-sectional view of an example HAMR head, in accordance with aspects of this disclosure. HAMR head  340  includes a waveguide  330 , an NFT  350 , a write pole  362 , a heat sink  355 , and a diffuser  336 . NFT  350  includes a plasmonic disk  353 , a near-field emitter  352 , and a middle disk  354 . 
     Waveguide  330  is disposed in an up-track direction relative to plasmonic disk  353 , near-field emitter  352 , and middle disk  354 . Waveguide  330  directs photons from a light source (e.g., laser  226  of  FIG.  2   ) toward NFT  350 . In some examples, waveguide  330  includes multiple optical layers. Waveguide  330 , for example, may include a waveguide core  332  and a core-to-NFT spacing (CNS) layer  334 . CNS layer  334  may be part of a cladding structure that also includes a rear cladding layer  331  and/or a front cladding layer  333 . In some examples, waveguide core  332  includes a first dielectric material (e.g., niobium oxide, tantalum oxide) of a first refractive index, and CNS layer  334  includes a second dielectric material (e.g., aluminum oxide, silicon dioxide) of a second refractive index. Photons directed by waveguide  330  toward NFT  350  may couple to free electrons of NFT  350  and excite one or more LSP resonance modes of NFT  350 . 
     NFT  350  is configured to amplify and emit a near-field  394  to produce a hot spot  387  on a magnetic disk  308 . Near-field  394  and a magnetic field from write pole  362  are directed to be partially coincident on spot  387  such that the temperature increase resulting from near-field  394  reduces the magnetic coercivity of the grains within hot spot  387  and enables the magnetic field from write pole  362  to orient them more easily, thus producing more stable bits of written data upon cooling. 
     Heat sink  355  is disposed in a down-track direction relative to middle disk  354  and is coupled to middle disk  354 . In some examples, heat sink  355  and middle disk  354  are coupled to each other at an interface  374  that is substantially orthogonal to media-facing surface  305 . Interface  374  includes a down-track surface of middle disk  354  and an up-track surface of heat sink  355 . Heat sink  355  is configured to draw heat away from regions of NFT  350  and direct the heat toward other regions of HAMR head  340 . In the example of HAMR head  340 , heat sink  355  is coupled to diffuser  336 , with diffuser  336  disposed in a down-track direction relative to heat sink  355 . Diffuser  336  is a heat sink that is configured to draw heat from NFT  350  and dissipate the heat toward other areas of HAMR head  340  (e.g., toward other heat sinks). In some examples, drawing heat away from regions of NFT  350  that are prone to thermal degradation may reduce defect formation in NFT  350  and/or extend the operating lifetime of HAMR head  340 . Heat sink  355  and/or diffuser  336  may include a thermally conductive material (e.g., gold). In some examples, heat sink  355  includes rhodium, copper, tungsten, tantalum, iridium, platinum, ruthenium, nickel, iron, or combinations thereof. 
     Plasmonic disk  353  is disposed in an up-track direction relative to near-field emitter  352  and middle disk  354 . Plasmonic disk  353  is coupled to waveguide  330 . In some examples, plasmonic disk  353  and waveguide  330  are coupled to each other at an interface  370  that is substantially orthogonal to media-facing surface  305 . Interface  370  includes a down-track surface of waveguide  330  and an up-track surface of plasmonic disk  353 . 
     Plasmonic disk  353  is configured to generate and support LSPs through resonance coupling of electrons with incident photons which are generated by a light source (e.g., laser  226  of  FIG.  2   ) and are directed toward NFT  350  by waveguide  330 . Plasmonic disk  353  includes a plasmonic metal. As used herein, a plasmonic metal is a metal that possesses properties (e.g., electrical properties, optical properties) that promote resonance coupling between photons incident upon the plasmonic metal and free electrons of the plasmonic metal. Such resonant coupling of a photon with free electrons of the plasmonic metal may excite one or more plasmonic modes of the plasmonic metal, which may result in the generation of an LSP on a surface of the plasmonic metal. Plasmonic metals that demonstrate efficient plasmon generation in response to photons of a wavelength target or range are said to have a high plasmonic figure of merit. Examples of plasmonic metals include gold, silver, ruthenium, copper, aluminum, and/or rhodium. In some instances, plasmonic disk  353  includes one of these plasmonic metals, an alloy of one of these plasmonic metals, and/or another noble metal including palladium, osmium, iridium, or platinum. 
     Near-field emitter  352  is configured to emit near-field  394  to produce hot spot  387  on magnetic disk  308 . Near-field emitter  352  includes a peg  352 A and an anchor disk  352 B. Peg  352 A is disposed proximal to a media-facing surface  305  of HAMR head  340 . In some instances, one or more portions of peg  325 A are exposed on media-facing surface  305 . Peg  352 A is configured to receive and amplify a near-field of the distribution of LSPs and emit near-field  394  to produce hot spot  387  on magnetic disk  308 . 
     Anchor disk  352 B is disposed behind peg  352 A relative to media-facing surface  305  (e.g., in the +y dimension, opposite the −y media-facing dimension). Anchor disk  352 B is coupled to plasmonic disk  353 . In some examples, anchor disk  352 B and plasmonic disk  353  are coupled to each other at an interface  373  that is substantially orthogonal to media-facing surface  305 . Interface  373  includes a down-track surface of plasmonic disk  353  and an up-track surface of anchor disk  352 B. Anchor disk  352 B is coupled to middle disk  354 . In some examples, middle disk  354  and anchor disk  352 B are coupled to each other at an interface  372  that is substantially orthogonal to media-facing surface  305 . Interface  372  includes a down-track surface of anchor disk  352 B and an up-track surface of middle disk  354 . 
     Anchor disk  352 B is configured to support a distribution of LSPs. In some examples, anchor disk  352 B is configured to participate in LSP generation. For example, peg  352 A may generate hotspot  387  by receiving and condensing a distribution of LSPs from anchor disk  352 B and/or other features, amplifying a near-field of the LSP distribution, and emitting amplified near-field  394  toward the surface of magnetic disk  308 . 
     In some examples, near-field emitter  352  is a single, continuous feature comprising peg  352 A and anchor disk  352 B. That is, peg  352 A and anchor disk  352 B may be regions or features of a single piece. Near-field emitter  352  may, for example, be deposited during a single manufacturing level or step (e.g., a photolithography level, a metal deposition step), with the shape and dimensions of the peg  352 A and anchor disk  352 B defined by a lithography pattern. In these examples, near-field emitter  352  may taper or narrow toward peg  352 A. Peg  352 A may protrude from anchor disk  352 B in the vicinity of media-facing surface  305  to enable LSPs to be transferred from anchor disk  352 B to peg  352 A and to enable peg  352 A to amplify and emit near-field  394  toward magnetic disk  308 . In some examples, peg  352 A and anchor disk  352 B each include one or more of the same materials. For example, peg  352 A and anchor disk  352 B may both include iridium, rhodium, ruthenium, gold alloy(s), gold composite(s) (e.g., a gold-nanoparticle composite), or combinations thereof. 
     Middle disk  354  is disposed in a down-track direction relative to near-field emitter  352  and is coupled to anchor disk  352 B. In some examples, middle disk  354  is configured to direct localized surface plasmons toward peg  352 A of near-field emitter  352 . In some examples, middle disk  354  is configured to mitigate background fields. 
     In accordance with aspects of this disclosure, middle disk  354  has a high melting temperature (e.g., at least 1500° C.). In some examples, middle disk  354  has a melting temperature of at least 1800° C. or at least 2200° C. A middle disk  354  having a high melting temperature may increase the lifespan of NFT  350  by reducing the likelihood of melting, void formation, diffusion, densification, and/or other defects at temperatures that are reached in a HAMR head under normal operating conditions. 
     A high melting temperature may be achieved by including one or more metals in middle disk  354 . For example, middle disk  354  may include a transition metal. A transition metal of middle disk  354  may be a platinum group metal (e.g., iridium, ruthenium, rhodium, osmium, platinum, palladium). 
     In some examples, the transition metal is a primary metal of middle disk  354 . As used herein the term “primary metal” refers to a metal that is present in a feature in an amount (e.g., atomic percentage or weight percentage) that is greater than any other metal that is also present in the same feature. That is, the primary metal constitutes greater than 50 atomic percent of middle disk  354  while the other portion of middle disk  354  includes one or more other materials. For example, the primary metal constitutes at least 50 atomic percent of middle disc  354 . In some examples, the primary metal constitutes at least 90 atomic percent of middle disc  354  (e.g., 95%, 99%, 99.9%). 
     In some examples, the transition metal is a component of an alloy of middle disk  354 . That is, the transition metal may be included with one or more other metals (e.g., other transition metals such as gold, non-transition metals) to form an alloy of middle disk  354 . 
       FIG.  4    is a perspective view of an example HAMR head, in accordance with aspects of this disclosure.  FIG.  4    may be a perspective view of HAMR head  340  of  FIG.  3   , with the view of the section of HAMR head  340  illustrated in  FIG.  3    indicated by the line  3 - 3  of  FIG.  4    facing in the direction of the arrows. HAMR head  440  includes an NFT  450  and a heat sink  455 . NFT  450  includes a plasmonic disk  453 , a near-field emitter  452 , and a middle disk  454 . 
     Heat sink  455  is disposed in a down-track direction relative to the middle disk  454 . Heat sink  455  and middle disk  454  are coupled to each other at an interface  474 . In some examples, interface  474  is substantially orthogonal to a media-facing surface  405  and substantially parallel to cross-track and media-facing dimensions (z and y, respectively) of HAMR head  440 . 
     Near-field emitter includes a peg  452 A and an anchor disk  452 B. Peg  452 A is disposed proximal to media-facing surface  405  of HAMR head  440 . Anchor disk  452 B is disposed behind peg  452 A relative to media-facing surface  405 . In some examples, near-field emitter  452  is a single, continuous feature including peg  452 A and anchor disk  452 B. Anchor disk  452 B occupies an area of a plane that is defined by a cross-track dimension (z) of HAMR head  440  and a media-facing dimension (y) of HAMR head  440  (hereafter, a near-field emitter plane). The near-field emitter plane may be orthogonal to media-facing surface  405 . Peg  452 A occupies an area of the near-field emitter plane that is smaller than the area of the near-field emitter plane that is occupied by anchor disk  452 B. 
     Plasmonic disk  453  is disposed in an up-track direction relative to the near-field emitter  452 . Anchor disk  452 B is coupled to plasmonic disk at an interface  473 . In some examples, interface  473  is substantially orthogonal to media-facing surface  405 . 
     Middle disk  454  is disposed in a down-track direction relative to near-field emitter  452 . Anchor disk  452 B is coupled to middle disk  454  at an interface  472 . In some examples, interface  472  is substantially orthogonal to media-facing surface  405 . Middle disk  454  includes a thermally stable primary metal. 
       FIG.  5    is a cross-sectional view of an example HAMR head, in accordance with aspects of this disclosure. HAMR head  540  includes a waveguide  530 , an NFT  550 , a write pole  562 , a heat sink  555 , and a diffuser  536 . NFT  550  includes a plasmonic disk  553 , a near-field emitter  552 , and a middle disk  554 . 
     Waveguide  530  is disposed in an up-track direction relative to plasmonic disk  553 , near-field emitter  552 , and middle disk  554 . In some examples, waveguide  530  includes multiple optical layers. Waveguide  530 , for example, may include a waveguide core  532  and a core-to-NFT spacing (CNS) layer  534 . CNS layer  534  may be part of a cladding structure that also includes a rear cladding layer  531  and/or a front cladding layer  533 . In some examples, waveguide core  532  includes a first dielectric material (e.g., niobium oxide, tantalum oxide) of a first refractive index, and CNS layer  534  includes a second dielectric material (e.g., aluminum oxide, silicon dioxide) of a second, different refractive index. 
     Plasmonic disk  553  is disposed in an up-track direction relative to near-field emitter  552  and middle disk  554 . Plasmonic disk  553  is coupled to waveguide  530 . In some examples, plasmonic disk  553  and waveguide  530  are coupled to each other at an interface  570  that is substantially orthogonal to a media-facing surface  505  of HAMR head  540 . Interface  570  includes a down-track surface of waveguide  530  and an up-track surface of plasmonic disk  553 . 
     Near-field emitter  552  includes a peg  552 A and an anchor disk  552 B. Peg  552 A is disposed proximal to media-facing surface  505 . In some instances, one or more portions of peg  325 A are exposed on media-facing surface  505 . Anchor disk  552 B is disposed behind peg  552 A relative to media-facing surface  505  (e.g., in the +y dimension, opposite the −y media-facing dimension). Anchor disk  552 B is coupled to plasmonic disk  553 . In some examples, anchor disk  552 B and plasmonic disk  553  are coupled to each other at an interface  573  that is substantially orthogonal to media-facing surface  505 . Interface  573  includes a down-track surface of plasmonic disk  553  and an up-track surface of anchor disk  552 B. Anchor disk  552 B is coupled to middle disk  554 . 
     In some examples, near-field emitter  552  is a single, continuous feature including peg  552 A and anchor disk  552 B. That is, peg  552 A and anchor disk  552 B may be regions or features of a single piece. In these examples, near-field emitter  552  may taper or narrow toward peg  552 A. Peg  552 A protrudes from anchor disk  552 B in the vicinity of media-facing surface  505  to enable LSPs to be transferred from anchor disk  552 B to peg  552 A and to enable peg  552 A to amplify and emit a near-field toward magnetic disk. In one example, peg  552 A and anchor disk  552 B each include one or more of the same materials. In some examples, peg  552 A and anchor disk  552 B both include iridium, rhodium, ruthenium, gold alloy(s), gold composite(s) (e.g., a gold-nanoparticle composite), or combinations thereof. 
     Middle disk  554  is disposed in a down-track direction relative to near-field emitter  552  and is coupled to anchor disk  552 B. In some examples, middle disk  554  and anchor disk  552 B are coupled to each other at an interface  572  that is substantially orthogonal to media-facing surface  505 . Interface  572  includes a surface down-track surface of anchor disk  552 B and an up-track surface of middle disk  554 . 
     In some examples, middle disk  554  includes a primary metal. In some examples, the primary metal constitutes at least 50 atomic percent of middle disc  554 . In some examples, the primary metal constitutes at least 90 atomic percent of middle disc  554 . In some examples, the primary metal constitutes at least 95 atomic percent of middle disc  554 . In some examples, the primary metal constitutes at least 99 atomic percent of middle disc  554 . 
     Heat sink  555  is disposed in a down-track direction relative to middle disk  554  and is coupled to middle disk  554 . In some examples, heat sink  555  and middle disk  554  are coupled to each other at an interface  574  that is substantially orthogonal to a media-facing surface  505  of HAMR head  540 . Interface  574  includes a surface  584   S  of middle disk  554  and a surface  585   S  of heat sink  555 . 
     Heat sink  555  includes a core  555 A including a primary metal and a liner  555 B. Liner  555 B is coupled to core  555 A and is disposed along outer surfaces  585 A S1  and  585 A S2  of core  555 A. Middle disk  554  is disposed between and coupled to liner  555 B and anchor disk  552 B. 
     Liner  555 B includes a first portion  555 B A  that is substantially parallel to middle disk  554  and disposed between and coupled to middle disk  554  and core  555 A. Liner  555 B includes a second portion  555 B B  that is oriented substantially orthogonal to middle disk  554  and substantially parallel to a down-track dimension of the HAMR head  540 . 
     Heat sink  555  includes a down-track surface  585   S  on a side of heat sink  555  that is opposite middle disk  554 . Down-track surface  585   S  slopes away from media-facing surface  505  toward the down-track direction. Down-track surface  585   S  includes a surface  585 A S3  of core  555 A and an edge  585 B E  of liner  555 B. Down-track surface  585   S  is coupled to diffuser  536 . 
     In accordance with aspects of this disclosure, liner  555 B has a high melting temperature (e.g., at least 1500° C.). In some examples, liner  555 B has a melting temperature of at least 1800° C. or at least 2200° C. Disposing a liner  555 B having a high melting temperature along one or more outer surfaces of core  555 A may reduce thermal defect formation in a core  555 A (e.g., a core  555 A that includes gold). For example, a liner  555 B having a high melting temperature may reduce recession of a core  555 A that includes gold, wherein the recession initiates near peg  552 A and progresses away from media-facing surface  505 . In some examples, including a liner  555 B having a high melting temperature may reduce or eliminate delamination between middle disk  554  and heat sink  555  when HAMR head  540  is exposed to thermal stress. Including a liner  555 B having a high melting temperature may enable heat sink  555  to dissipate heat more effectively over extended operation of HAMR head  540  and may extend the lifetime of HAMR head  540 . 
     A high melting temperature may be achieved by including one or more metals in liner  555 B. For example, liner  555 B may include a transition metal. A transition metal of liner  555 B may be a platinum group metal (e.g., iridium, ruthenium, rhodium, osmium, platinum, palladium). In some examples, the transition metal is a component of an alloy of liner  555 B. 
     In some examples, the transition metal is a primary metal of liner  555 B. That is, the transition metal may constitute at least 50 atomic percent of liner  555 B (e.g., 90%, 95%, 99%, 99.9%). In some scenarios, the primary metal of liner  555 B is different than the primary metal of core  555 A. 
       FIG.  6    is a perspective view of an example HAMR head, in accordance with aspects of this disclosure.  FIG.  6    may be a perspective view of HAMR head  540  of  FIG.  5   , with the view of the section of HAMR head  540  illustrated in  FIG.  5    indicated by the line  5 - 5  of  FIG.  6    facing in the direction of the arrows. HAMR head  640  includes an NFT  650  and a heat sink  655 . NFT  650  includes a plasmonic disk  653 , a near-field emitter  652 , and a middle disk  654 . 
     Near-field emitter includes a peg  652 A and an anchor disk  652 B. Peg  652 A is disposed proximal to a media-facing surface  605  of HAMR head  640 . Anchor disk  652 B is disposed behind peg  652 A relative to media-facing surface  605 . In some examples, near-field emitter  652  is a single, continuous feature including peg  652 A and anchor disk  652 B. Anchor disk  652 B occupies an area of a plane that is defined by a cross-track dimension (z) of HAMR head  640  and a media-facing dimension (y) of HAMR head  640  (hereafter, a near-field emitter plane). The near-field emitter plane may be orthogonal to media-facing surface  605 . Peg  652 A occupies an area of the near-field emitter plane that is smaller than the area of the near-field emitter plane that is occupied by anchor disk  652 B. 
     Plasmonic disk  653  is disposed in an up-track direction relative to the near-field emitter  652 . Anchor disk  652 B is coupled to plasmonic disk at an interface  673 . In some examples, interface  673  is substantially orthogonal to media-facing surface  605 . 
     Middle disk  654  is disposed in a down-track direction relative to near-field emitter  652 . Anchor disk  652 B is coupled to middle disk  654  at an interface  672 . In some examples, interface  672  is substantially orthogonal to media-facing surface  605 . Middle disk  654  may includes a thermally stable primary metal. 
     Heat sink  655  is disposed in a down-track direction relative to the middle disk  654 . Heat sink  655  and middle disk  654  are coupled to each other at an interface  674 . In some examples, interface  674  is substantially orthogonal to a media-facing surface  605  and substantially parallel to cross-track and media-facing dimensions (z and y, respectively) of HAMR head  640 . 
     Heat sink  655  includes a core  655 A including a primary metal, and a liner  655 B including a primary metal. Liner  655 B includes a first portion  655 B A  that is substantially parallel to middle disk  654  and disposed between and coupled to middle disk  654  and core  655 A. Liner  655 B includes a second portion  655 B B  that is oriented substantially orthogonal to middle disk  654  and substantially parallel to a down-track dimension of HAMR head  640 . Liner  655 B encloses core  655 A on a side  655 A S1  of core  655 A that faces near-field transducer  650  and on a curved outer surface  655 A S2  of core  655 A that is substantially parallel to a down-track dimension. Heat sink  655  includes a down-track surface  685   S  on a side of heat sink  655  that is opposite middle disk  654 . Down-track surface  685   S  slopes away from media-facing surface  605  toward the down-track direction. Down-track surface  685   S  includes a surface  685 A S3  of core  655 A and an edge  685 B E  of liner  655 B.