ABSTRACT
Recently, Heusler alloy-based spin gapless semiconductors (SGSs) with high Curie temperature (TC) 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 La1-xNaxMnO3 (≈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 La0.7Sr0.3MnO3 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.
ABSTRACT
The magnetic proximity effect (MPE) has recently been explored to manipulate interfacial properties of two-dimensional (2D) transition metal dichalcogenide (TMD)/ferromagnet heterostructures for use in spintronics and valleytronics. However, a full understanding of the MPE and its temperature and magnetic field evolution in these systems is lacking. In this study, the MPE has been probed in Pt/WS2/BPIO (biphase iron oxide, Fe3O4 and α-Fe2O3) heterostructures through a comprehensive investigation of their magnetic and transport properties using magnetometry, four-probe resistivity, and anomalous Hall effect (AHE) measurements. Density functional theory (DFT) calculations are performed to complement the experimental findings. We found that the presence of monolayer WS2 flakes reduces the magnetization of BPIO and hence the total magnetization of Pt/WS2/BPIO at T > ~120 K-the Verwey transition temperature of Fe3O4 (TV). However, an enhanced magnetization is achieved at T < TV. In the latter case, a comparative analysis of the transport properties of Pt/WS2/BPIO and Pt/BPIO from AHE measurements reveals ferromagnetic coupling at the WS2/BPIO interface. Our study forms the foundation for understanding MPE-mediated interfacial properties and paves a new pathway for designing 2D TMD/magnet heterostructures for applications in spintronics, opto-spincaloritronics, and valleytronics.
ABSTRACT
Temperature-dependent transport properties of the recently discovered layered bismuth-rich tellurobromides BinTeBr (n = 2, 3) are investigated for the first time. Dense homogeneous polycrystalline specimens prepared for different electrical and thermal measurements were synthesized by a ball milling-based process. While the calculated electronic structure classifies Bi2TeBr as a semimetal with a small electron pocket, its transport properties demonstrate a semiconductorlike behavior. Additional bismuth bilayers in the Bi3TeBr crystal structure strengthens the interlayer chemical bonding thus leading to metallic conduction. The thermal conductivity of the semiconducting compositions is low, and the electrical properties are sensitive to doping with a factor of four reduction in resistivity observed at room temperature for only 3% Pb doping. Investigation of the thermoelectric properties suggests that optimization for thermoelectrics may depend on particular elemental substitution. The results presented are intended to expand on the research into tellurohalides in order to further advance the fundamental investigation of these materials, as well as investigate their potential for thermoelectric applications.
