Identification of spin-dependent thermoelectric effects in metamagnetic FeRh/heavy-metal bilayers

Abstract

A vertical flux of heat can bring about hybrid generation of charge and spin currents and eventually convert into the transverse electric voltage in the bilayers composed of metallic magnet and non-magnetic heavy metal (HM). We identified the thermoelectric effects in the sputter-deposited metallic film of CsCl-ordered FeRh/HM throughout its metamagnetic transition from ferromagnetic (FM) to antiferromagnetic (AFM) phase. With the employment of different HMs (Pt, Au) as the spin detective layers, we found that the FM phase allows for hybrid generation of charge and spin currents by heat, respectively, attributed to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), while the AFM phase merely retains the ANE from residual nanoscale FM domains at cryogenic temperatures, which was further confirmed by the control measurement based on the adjustment of spin Hall angle for W during its β to α phase transition. Contribution from the proximity-induced ANE of HM was verified to be negligible compared with that of ANE and SSE of FeRh. Our method opens up more access to quantitatively discern the entangled thermo-charge/spin contributions in metallic magnets, and the combination of thermoelectric effects with metamagnetic phase transition gives impetus to exploiting more versatile and energy-saving thermo-spin logic applications.