Unconventional transport properties of an itinerant ferromagnet: EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20)

Abstract

We report the temperature and magnetic field dependence of resistivity ($\rho$) for single-crystalline EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20), an itinerant ferromagnetic system with very low Curie temperature ($T_C$). The detailed analysis reveals that the charge conduction in EuTi$_{1-x}$Nb$_{x}$O$_3$ is extremely sensitive to Nb concentration and dominated by several scattering mechanisms. Well below the $T_C$, where the spontaneous magnetization follows the Bloch's $T^{3/2}$ law, $\rho$ exhibits $T^2$ dependence with a large coefficient $\sim$10$^{-8}$ $\Omega$ cm K$^{-2}$ due to the electron-magnon scattering. Remarkably, all the studied samples exhibit a unique resistivity minimum at $T$$=$$T_{\rm min}$ below which $\rho$ shows logarithmic increment with $T$ (for $T_{\rm C}$$<$$T$$<$$T_{\rm min}$) due to the Kondo scattering of Nb 4$d^1$ itinerant electrons by the localized 4$f$ moments of Eu$^{2+}$ ions which suppresses strongly with applied magnetic field. In the paramagnetic state, $T^{2}$ and $T^{3/2}$ dependence of the resistivity have been observed, suggesting an unusual crossover from a Fermi-liquid to a non-Fermi-liquid behavior with increasing $T$. The observed temperature and magnetic field dependence of resistivity has been analysed using different theoretical models.