Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4

TL;DR

This study investigates the anisotropic colossal magnetoresistance effects in Fe_{1-x}Cu_xCr_2S_4 single crystals, revealing how magnetic anisotropy and field direction influence transport properties at low temperatures.

Contribution

It provides a detailed experimental analysis of magnetic anisotropy and magnetoresistance dependence on field direction in Fe_{1-x}Cu_xCr_2S_4, incorporating both ionic and band models.

Findings

Magnetic anisotropy develops below the Curie temperature and is affected by Cu concentration.

Magnetoresistance shows strong directional dependence, with sign changes when field is applied along different axes.

Magnetoresistance remains positive at low temperatures, with a maximum influenced by magnetic field orientation.

Abstract

A detailed study of the electronic transport and magnetic properties of Fe$_{1-x}$Cu$_x$Cr$_2$S$_4$ ($x \leq 0.5$) on single crystals is presented. The resistivity is investigated for $2 \leq T \leq 300$ K in magnetic fields up to 14 Tesla and under hydrostatic pressure up to 16 kbar. In addition magnetization and ferromagnetic resonance (FMR) measurements were performed. FMR and magnetization data reveal a pronounced magnetic anisotropy, which develops below the Curie temperature, $T_{\mathrm{C}}$, and increases strongly towards lower temperatures. Increasing the Cu concentration reduces this effect. At temperatures below 35 K the magnetoresistance, $MR = \frac{\rho(0) - \rho(H)}{\rho(0)}$, exhibits a strong dependence on the direction of the magnetic field, probably due to an enhanced anisotropy. Applying the field along the hard axis leads to a change of sign and a strong increase of the absolute value of the magnetoresistance. On the other hand the magnetoresistance remains positive down to lower temperatures, exhibiting a smeared out maximum with the magnetic field applied along the easy axis. The results are discussed in the ionic picture using a triple-exchange model for electron hopping as well as a half-metal utilizing a band picture.