Large Thermo-Spin Effects in Heusler Alloy-Based Spin Gapless Semiconductor Thin Films

Amit Chanda; Deepika Rani; Derick DeTellem; Noha Alzahrani; Dario A Arena; Sarath Witanachchi; Ratnamala Chatterjee; Manh-Huong Phan; Hariharan Srikanth

doi:10.1021/acsami.3c12342

Large Thermo-Spin Effects in Heusler Alloy-Based Spin Gapless Semiconductor Thin Films

ACS Appl Mater Interfaces. 2023 Nov 22;15(46):53697-53713. doi: 10.1021/acsami.3c12342. Epub 2023 Nov 8.

Authors

Amit Chanda¹, Deepika Rani², Derick DeTellem¹, Noha Alzahrani¹, Dario A Arena¹, Sarath Witanachchi¹, Ratnamala Chatterjee², Manh-Huong Phan¹, Hariharan Srikanth¹

Affiliations

¹ Department of Physics, University of South Florida, Tampa, Florida 33620, United States.
² Physics Department, Indian Institute of Technology Delhi, New Delhi 110016, India.

PMID: 37939351
DOI: 10.1021/acsami.3c12342

Abstract

Recently, Heusler alloy-based spin gapless semiconductors (SGSs) with high Curie temperature (T_C) and sizable spin polarization have emerged as potential candidates for tunable spintronic applications. We report comprehensive investigation of the temperature-dependent ANE and intrinsic longitudinal spin Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our findings show that the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm) film is ≈1.86 μV K^-1 at room temperature, which is nearly 2 orders of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (≈0.018 μV K^-1) and almost 3 orders of magnitude higher than that of the half-metallic ferromagnet La_1-xNa_xMnO₃ (≈0.005 μV K^-1) but comparable to that of the magnetic Weyl semimetal Co₂MnGa thin film (≈2-3 μV K^-1). Furthermore, the LSSE coefficient for our MgO/CoFeCrGa (95 nm)/Pt (5 nm) heterostructure is ≈20.5 nV K^-1 Ω^-1 at room temperature, which is twice larger than that of the half-metallic ferromagnetic La_0.7Sr_0.3MnO₃ thin films (≈9 nV K^-1 Ω^-1). We show that both ANE and LSSE coefficients follow identical temperature dependences and exhibit a maximum at ≈225 K, which is understood as the combined effects of inelastic magnon scatterings and reduced magnon population at low temperatures. Our analyses not only indicate that the extrinsic skew scattering is the dominating mechanism for ANE in these films but also provide critical insights into the functional form of the observed temperature-dependent LSSE at low temperatures. Furthermore, by employing radio frequency transverse susceptibility and broad-band ferromagnetic resonance in combination with the LSSE measurements, we establish a correlation among the observed LSSE signal, magnetic anisotropy, and Gilbert damping of the CoFeCrGa thin films, which will be beneficial for fabricating tunable and highly efficient Heusler alloy-based spin caloritronic nanodevices.

Keywords: Gilbert damping; Heusler alloy; anomalous Nernst effect; longitudinal spin Seebeck effect; magnetic anisotropy; spin gapless semiconductor.