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

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−x Na x MnO 3 (≈0.005 μV K −1 ) but comparable to that of the magnetic Weyl semimetal Co 2 MnGa 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 0.7 Sr 0.3 MnO 3 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.

Temperature Evolution of Magnon Propagation Length in Tm3Fe5O12 Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping

“…To quantify the temperature evolution of ⟨ξ⟩ for our TmIG/Pt bilayer films, we have employed a model proposed by Jimenez-Cavero et al, according to which the total temperature difference (Δ T ) across the GSGG/TmIG/Pt heterostructure can be expressed as a linear combination of temperature drops in the Pt layer, at the TmIG/Pt interface, in the TmIG layer, at the GSGG/TmIG interface,and across the GSGG substrate as well as in the N-grease layers (thickness ∼1 μm) on both sides of the GSGG/TmIG heterostructures as, Δ T = Δ T P t + Δ T normalPt / normalTmIG + Δ T TmIG + Δ T normalTmIG / normalGSGG + Δ T GSGG + 2 Δ T N ‐grease (see Figure a). Assuming negligible drops in Δ T in the Pt layer and at the GSGG/TmIG and Pt/TmIG interface, , the total temperature difference can be approximately written as Δ T = Δ T normalPt / normalTmIG + Δ T TmIG + Δ T GSGG + 2 Δ T N ‐g r e a s e Considering these contributions, the temperature drops in the TmIG layer and at the TmIG/Pt interface can be written as ,…”

“…(see Figure 5a). Assuming negligible drops in ΔT in the Pt layer and at the GSGG/TmIG and Pt/TmIG interface, 68,69 the total temperature difference can be approximately written as Considering these contributions, the temperature drops in the TmIG layer and at the TmIG/Pt interface can be written as 68,69 = + + T T…”