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Title: Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications

Abstract

Here, we report on the out-of-plane thermal conductivities of tetragonal L1 0 FePt (001) easy-axis and cubic A1 FePt thin films via time-domain thermoreflectance over a temperature range from 133 K to 500 K. The out-of-plane thermal conductivity of the chemically ordered L10 phase with alternating Fe and Pt layers is ~23% greater than the thermal conductivity of the disordered A1 phase at room temperature and below. However, as temperature is increased above room temperature, the thermal conductivities of the two phases begin to converge. Molecular dynamics simulations on model FePt structures support our experimental findings and help shed more light into the relative vibrational thermal transport properties of the L1 0 and A1 phases. Furthermore, unlike the varying temperature trends in the thermal conductivities of the two phases, the electronic scattering rates in the out-of-plane direction of the two phases are similar for the temperature range studied in this work.

Authors:
 [1];  [2];  [2];  [3];  [1]
  1. Univ. of Virginia, Charlottesville, VA (United States)
  2. HGST, a Western Digital company, San Jose, CA (United States)
  3. Chemnitz Univ. of Technology, Chemnitz (Germany); Helmholtz-Zentrum Dresden- Rossendorf, Dresden (Germany)
Publication Date:
Research Org.:
Univ. of Virginia, Charlottesville, VA (United States). Dept. of Mechanical and Aerospace Engineering
Sponsoring Org.:
USDOE
OSTI Identifier:
1378367
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Information storage; Surfaces, interfaces and thin films

Citation Formats

Giri, Ashutosh, Wee, Sung Hun, Jain, Shikha, Hellwig, Olav, and Hopkins, Patrick E. Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications. United States: N. p., 2016. Web. doi:10.1038/srep32077.
Giri, Ashutosh, Wee, Sung Hun, Jain, Shikha, Hellwig, Olav, & Hopkins, Patrick E. Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications. United States. doi:10.1038/srep32077.
Giri, Ashutosh, Wee, Sung Hun, Jain, Shikha, Hellwig, Olav, and Hopkins, Patrick E. 2016. "Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications". United States. doi:10.1038/srep32077. https://www.osti.gov/servlets/purl/1378367.
@article{osti_1378367,
title = {Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications},
author = {Giri, Ashutosh and Wee, Sung Hun and Jain, Shikha and Hellwig, Olav and Hopkins, Patrick E.},
abstractNote = {Here, we report on the out-of-plane thermal conductivities of tetragonal L10 FePt (001) easy-axis and cubic A1 FePt thin films via time-domain thermoreflectance over a temperature range from 133 K to 500 K. The out-of-plane thermal conductivity of the chemically ordered L10 phase with alternating Fe and Pt layers is ~23% greater than the thermal conductivity of the disordered A1 phase at room temperature and below. However, as temperature is increased above room temperature, the thermal conductivities of the two phases begin to converge. Molecular dynamics simulations on model FePt structures support our experimental findings and help shed more light into the relative vibrational thermal transport properties of the L10 and A1 phases. Furthermore, unlike the varying temperature trends in the thermal conductivities of the two phases, the electronic scattering rates in the out-of-plane direction of the two phases are similar for the temperature range studied in this work.},
doi = {10.1038/srep32077},
journal = {Scientific Reports},
number = 1,
volume = 6,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
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  • A comparison was made of FePt-B and FePt-B-Ag thin films having different volume contents of boron, which were RF sputtered with in-situ heating at 425-575 deg. C onto Si substrates with 20 nm thick (002) MgO. By introducing boron into FePt and varying the sputtering conditions, films with grain sizes ranging from 2.5 to 10 nm were produced. The boron promoted columnar growth, but made ordering more difficult. However, by adding Ag into FePt-B, ordering improved while coercivity increased from 7 to 11 kOe with no significant impact on the microstructure. We obtained films with grain sizes down to 2.5more » nm with center-to-center spacing of 3.1 nm. The reduced grain size, columnar microstructure and increase in ordering and coercivity by adding Ag into the FePt-B thin films are favorable for application in heat assisted magnetic recording.« less
  • We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L1{sub 0} FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated.
  • We investigated the Ag distribution in a FePtAg-C granular film that is under consideration for a heat assisted magnetic recording medium by aberration-corrected scanning transmission electron microscope-energy dispersive X-ray spectroscopy and X-ray absorption fine structure. Ag is rejected from the core of FePt grains during the deposition, forming Ag-enriched shell surrounding L1{sub 0}-ordered FePt grains. Since Ag has no solubility in both Fe and Pt, the rejection of Ag induces atomic diffusions thereby enhancing the kinetics of the L1{sub 0}-order in the FePt grains.
  • In heat-assisted magnetic recording, optical energy is transferred to a small optical spot on the recording media using a near field transducer. In this study, a scattered field finite difference time domain simulation is used to analyze the performance of a lollipop transducer in heat assisted magnetic recording on both a patterned FePt media and a continuous thin film. To represent wear, sharp corners of the peg are approximated with curved ones, which are found to narrow the track width without excessive loss of intensity. Compared with continuous media, the patterned media exhibits higher energy efficiency and a better concentratedmore » optical beam spot. This effect is due to the near field effects of patterned media on the performance of the transducer.« less
  • Recently a novel media structure for thermally assisted magnetic recording was proposed consisting of a layer of FePt exchange coupled to a FeRh layer. The FePt forms a high magnetocrystalline anisotropy, high coercivity ferromagnetic layer. The FeRh layer is antiferromagnetic at room temperature, but upon heating above a transition temperature becomes ferromagnetic with a large magnetic moment and low magnetocrystalline anisotropy. The coupled ferromagnetic FePt and FeRh layers form an exchange-spring system significantly lowering the coercive field of the composite system compared to a single layer of FePt. This feature opens intriguing possibilities for media applications for thermally assisted magneticmore » recording where the ferromagnetic phase of FeRh is exploited to help write the media while the low-temperature antiferromagnetic phase supports the long-term stability. Here temperature-dependent structural and magnetic measurements of undoped and doped FeRh single layer and FePt-FeRh bilayer films are presented and the promises and challenges of the exchange spring media structure are discussed.« less