Temperature dependent transport spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi_1−xNb_xO₃

Abstract

The physical systems with ferromagnetism and "bad" metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi1−xNbxO3 emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a T2 temperature dependence possibly due to electron-magnon scattering and above the Curie temperature Tc, the dependence changes to T3/2 behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization in EuTi_1−xNb_xO₃, a low Curie temperature ferromagnet, is as high (∼40%) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi_1−xNb_xO₃, the temperature (T) dependence of Pt could be measured systematically up to Tc which revealed a proportionate relationship with magnetization Ms vs. T. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped understand the origin of such high spin polarization in EuTi_1−xNb_xO₃ but also provided a route to estimate the Hubbard U parameter in complex metallic ferromagnets in general using experimental inputs.