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

TL;DR

This study investigates the unusual electrical transport behaviors of EuTi$_{1-x}$Nb$_{x}$O$_3$, revealing complex scattering mechanisms, a resistivity minimum linked to Kondo effects, and a crossover from Fermi-liquid to non-Fermi-liquid behavior.

Contribution

It provides a detailed analysis of resistivity in EuTi$_{1-x}$Nb$_{x}$O$_3$, highlighting the impact of Nb doping, Kondo scattering, and magnetic field effects on transport properties, which is novel for this itinerant ferromagnet.

Findings

Resistivity exhibits a $T^2$ dependence below $T_C$ due to electron-magnon scattering.

A resistivity minimum at $T_{min}$ indicates Kondo scattering by Nb electrons.

Unusual crossover from Fermi-liquid to non-Fermi-liquid behavior with increasing temperature.

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.