Optimizing the Optical and Thermal Design of Heat-Assisted Magnetic Recording Media

Jubert, Pierre‐Olivier; Zong, Fenghua; Grobis, M.

doi:10.1109/tmag.2016.2604261

Cited by 8 publications

(2 citation statements)

References 16 publications

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“…The in-plane thermal conductivity is known to have a significant effect on the temperature gradient and the laser power required to attain a fixed trackwidth. 7) Ballistic effects on in-plane thermal conductivity and lateral heat flow may therefore be significant and could be investigated by extension of the model. The ballistic contribution to transient heat transfer can also be incorporated using the lumped heat capacity method 8) in which the temperature is regarded to be constant within each layer as well as 3D finite element models.…”

Section: Discussionmentioning

confidence: 99%

“…Heat-assisted magnetic recording (HAMR) allows writing on media with very high coercivity such as chemically ordered granular L1 0 FePt:X thin films, 1) with areal density capacity beyond 1 Tbit in −2 . The thermal transport in HAMR multilayers is of interest [2][3][4][5][6][7][8] due to the critical importance of the temperature in nucleating magnetic reversal and defining the position of magnetic transitions. The magnetization switches direction along the write field when the temperature is smaller but close to the Curie temperature T ; T c .…”

Section: Introductionmentioning

confidence: 99%

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Model of ballistic-diffusive thermal transport in HAMR media

Lyberatos

Parker

2019

Jpn. J. Appl. Phys.

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A model is presented that considers the grain size and temperature dependence of the thermal conductivity and specific heat of L1 0 FePt nanoparticles and is applied to study the temperature distribution within the top recording layer in heat assisted magnetic recording. Ballistic effects on the thermal conductivity are included assuming diffuse scattering of the electron heat carriers at interfaces and grain boundaries. The magnetic contribution to the specific heat during laser heating close to the Curie temperature is determined using Monte Carlo simulations based on the effective classical spin Hamiltonian of chemically ordered L1 0 FePt. Following the application of a nanosecond laser pulse, the perpendicular heat flow through a FePt/MgO/heat-sink stack is calculated using the finite element method. The temperature drop across the thickness of the FePt layer is shown to be significant for grains of small in-plane size. Size induced grain temperature variations are small due to the temperature dependence of the specific heat of FePt, so the resultant contribution to transition jitter is expected to be limited in extent.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Model of ballistic-diffusive thermal transport in HAMR media

Lyberatos

Parker

2019

Jpn. J. Appl. Phys.

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Thermal stability and magnetization reversal mechanism in granular L1 FePt thin films

Pǎpuşoi

Jain

Yuan

et al. 2017

Journal of Applied Physics

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The relationship between coercivity HC and magneto-crystalline anisotropy field HK of L10 FePt granular alloy thin films is investigated as a function of film thickness in the range of 3.5–12.5 nm. While HK exhibits a decrease from 82 kOe to 71 kOe with increasing film thickness, HC displays a pronounced peak at a critical film thickness of tCR ≅ 7 nm. In order to explain the non-monotonic behavior of HC as a function of film thickness, the time dependence of HC at ambient temperature (TRT = 300 K) and the temperature dependence of the AC susceptibility in the range TRT – 800 K are measured as a function of film thickness and interpreted in the frame of the Stoner–Wohlfarth model of coherent rotations. It is demonstrated that the HC decrease with increasing film thickness above tCR is a consequence of a transition from coherent to an incoherent magnetization reversal mechanism in isolated grains. For a 7 nm thick film (tCR), the average grain size of ∼7.4 nm is comparable with the film thickness, suggesting that the domain-wall (DW) width δ ≅ tCR. Previous theoretical work has demonstrated a strong dependence of δ on the orientation of the DW with respect to the (001) planes of an L10 FePt lattice. By using the values of the micromagnetic exchange coupling A theoretically evaluated for parallel and vertical DW orientation with respect to the (001) planes, one obtains δ = 5.2 nm for parallel and δ = 6.7 nm for vertical DWs. The latter is closer to the experimental value of δ, suggesting that the nucleation of vertical DWs inside the grains (probably at grain boundaries) is the dominant mechanism responsible for the incoherent magnetization reversal evidenced in the investigated films.

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Using structural phase transitions to enhance the coercivity of ferromagnetic films

et al. 2019

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Storing information in magnetic recording technologies requires careful optimization of the recording media’s magnetic properties. For example, heat-assisted magnetic recording (HAMR) relies on a prerecording heating step that momentarily lowers the coercivity of the ferromagnetic recording media, and thereby decreases the energy expenditure for each writing operation. However, this process currently requires local temperature increases of several hundred Kelvins, which in turn can cause heat spreading, damage the write head, and limit recording rates. Here, we describe a general mechanism for dramatically tuning the coercivity of ferromagnetic films over small temperature ranges, by coupling them to an adjacent layer that undergoes a structural phase transition with large volume changes. The method is demonstrated in Ni/FeRh bilayers where the Ni layer was deposited at 300 K and 523 K, above and below the FeRh metamagnetic transition at 370 K. When the Ni layer is grown at high temperatures, the 1% FeRh lattice expansion relative to room temperature alters the Ni’s crystallographic texture during growth and leads to a 500% increase in coercivity upon cooling through the FeRh’s metamagnetic transition. Our analysis suggests this effect is related to domain wall pinning across grain boundaries with different orientations and strain states. This work highlights the promise of thermally tuning the coercivity of ferromagnetic materials through structural coupling to underlying films that could enable simplified heatsink designs and expand the selection of materials compatible with HAMR.

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Optimizing the Optical and Thermal Design of Heat-Assisted Magnetic Recording Media

Cited by 8 publications

References 16 publications

Model of ballistic-diffusive thermal transport in HAMR media

Model of ballistic-diffusive thermal transport in HAMR media

Thermal stability and magnetization reversal mechanism in granular L1 FePt thin films

Using structural phase transitions to enhance the coercivity of ferromagnetic films

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