The anomalous Hall Effect and magnetoresistance in the layered ferromagnet Fe_{1/4}TaS_2: the inelastic regime

TL;DR

This study investigates the anomalous Hall effect and magnetoresistance in Fe_{1/4}TaS_2, revealing temperature-dependent behaviors and inelastic contributions, with implications for understanding ferromagnetic transport phenomena.

Contribution

It identifies an inelastic AHE conductivity component scaling with resistivity squared and explains complex magnetoresistance features in Fe_{1/4}TaS_2.

Findings

Inelastic AHE conductivity scales as $( ho- ho_0)^2$ above 50 K.

Temperature-independent AHE conductivity at low T aligns with Berry-phase theory.

Magnetoresistance exhibits complex behavior explained by anisotropic effects and magnon suppression.

Abstract

The large magnetic anisotropy in the layered ferromagnet Fe_{1/4}TaS_2 leads to very sharp reversals of the magnetization $\bf M$ at the coercive field. We have exploited this feature to measure the anomalous Hall effect (AHE), focussing on the AHE conductivity $\sigma^A_{xy}$ in the inelastic regime. At low temperature T (5-50 K), $\sigma^A_{xy}$ is T-independent, consistent with the Berry-phase/Karplus-Luttinger theory. Above 50 K, we extract an inelastic AHE conductivity $\sigma^{in}_{xy}$ that scales as the square of $\Delta\rho$ (the T dependent part of the resistivity $\rho$). The term $\sigma^{in}_{xy}$ clarifies the T dependence and sign-reversal of the AHE coefficient R_s(T). We discuss the possible ubiquity of $\sigma^{in}_{xy}$ in ferromagnets, and ideas for interpreting its scaling with $(\Delta\rho)^2$. Measurements of the magnetoresistance (MR) reveal a rich pattern of behavior vs. T and field tilt-angle. We show that the 2 mechanisms, the anisotropic MR effect and field-suppression of magnons, account for the intricate MR behavior, including the bow-tie features caused by the sharp reversals in $\bf M$.