Magnetic-anisotropy-enhanced electrical transport properties of Co/Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/PVDF flexible thermoelectromagnetic films

A built-in magnetic field by magnetic embedding has been proven to be an effective approach to improve the electro-thermal conversion performance of thermoelectric materials. However, the function of the built-in magnetic field direction is still unknown. In this study, ferromagnetic Co particles with different morphologies are introduced into Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/PVDF thermoelectric films to control the direction of the built-in magnetic field. Co particles with shape anisotropy establish magnetic anisotropy fields inside the flexible thermoelectromagnetic films, which make the magnetic moments tend to be aligned parallel to the film surface, causing spiral motion of carriers. The atomic-scale micro-electric field established by the in situ reaction of Co and Te induces hopping migration of carriers. The coupling of the magnetic anisotropy field and micro-electric field brings about a substantial increase in carrier mobility, thus greatly enhancing conductivity. The carrier energy filtering effect generated by Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/CoTe${}_2$/Co hetero interface and additional magnetic scattering provided by the CoTe${}_2$/Co micro-magnetic field maintain the Seebeck coefficient at a high level. The maximum power factor of Co/Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/PVDF flexible thermoelectromagnetic film with sheet Co particles reaches 1.45 mW m${}^{-1}$ K${}^{-2}$ at 300 K, increased by 54% and 6% as compared with that of Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/PVDF thermoelectric film and Co/Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$/PVDF flexible thermoelectromagnetic film with spherical Co particles, respectively. (© 2022 Wiley‐VCH GmbH)