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Substrate-dependent Magneto-Thermoelectric Properties in FeRh Thin Films during Antiferromagnetic-Ferromagnetic Phase Transition
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  • Sabbir Akhanda,
  • Sourav Das,
  • Megan Lenox,
  • Benjamin Aronson,
  • Shelby Fields,
  • Steven Bennett,
  • Jae Won Choi,
  • Jung-Min Cho,
  • Bellave Shivaram,
  • Sang-Kwon Lee,
  • Jon Ihlefeld,
  • Mona Zebarjadi
Sabbir Akhanda
University of Virginia
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Sourav Das
University of Virginia
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Megan Lenox
University of Virginia
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Benjamin Aronson
University of Virginia
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Shelby Fields
US Naval Research Laboratory
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Steven Bennett
US Naval Research Laboratory
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Jae Won Choi
Chung-Ang University - Seoul Campus
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Jung-Min Cho
Chung-Ang University - Seoul Campus
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Bellave Shivaram
University of Virginia
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Sang-Kwon Lee
Chung-Ang University - Seoul Campus
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Jon Ihlefeld
University of Virginia
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Mona Zebarjadi
University of Virginia

Corresponding Author:mz6g@virginia.edu

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Abstract

FeRh is an intermetallic magnetic compound featuring a B2-ordered structure and exhibiting a first-order antiferromagnetic (AFM) to ferromagnetic (FM) phase transition near room temperature. Here, we explore the magneto-thermoelectric properties encompassing the resistivity, Seebeck coefficient, and Thomson coefficient in near-equimolar FeRh thin films grown on three different substrates, namely Al2O3 (sapphire), SiO2/Si, and MgO. The substrate affects the phase transition temperature by inducing in-plane strain (compressive for MgO, tensile for sapphire and SiO2/Si), while film thickness shifts the transition to higher temperatures. At the same thickness of 80 nm, the MgO films have the highest phase transition temperature, the hysteresis loop of sapphire films starts at around 300K, and that of SiO2/Si shifts to 200K. While the Seebeck coefficient in the FM phase remains negative consistently, the Seebeck coefficient of the AFM phase varies in sign depending on the substrate, film quality, and thickness. The larger negative Seebeck coefficient values in the FM phase are attributed to the larger FM density of states around the Fermi level. We discuss the role of crystal quality in designing a pathway for heightened Thomson response in FeRh thin films. Within the monitored temperature range, Thomson coefficient values as large as -250 µV.K−1 were observed with non-negligible values in a 50 K temperature range. We also observe a larger Nernst thermopower in the FM phase, the lower-mobility phase, and an unusual sign change in the AFM phase.