Paramagnetic to ferromagnetic phase transition in lightly Fe-doped Cr$_2$B

TL;DR

This study demonstrates how light Fe doping induces a paramagnetic to ferromagnetic phase transition in Cr$_2$B, revealing a quantum phase transition near 2% doping with observable magnetic and electronic changes.

Contribution

It reports the first observation of ferromagnetism in lightly Fe-doped Cr$_2$B and identifies a quantum phase transition around 2% Fe doping.

Findings

Ferromagnetism appears with less than 3% Fe doping.

Curie-Weiss temperature shifts from negative to positive with doping.

T$_C$ increases linearly with Fe doping, reaching 46 K at 5%.

Abstract

Cr$_2$B displays temperature independent paramagnetism. We induce ferromagnetism by replacing less than $3\,\%$ of the Cr atoms by Fe. By the lowest Fe doping level made, Curie-Weiss behavior is observed; $\Theta_{CW}$ changes from $-20\,$K for $0.5\,\%$ Fe-doped Cr$_2$B to positive values of about 50 K by $5\,\%$ Fe doping. The ferromagnetic T$_C$ is 8 K for $2.5\,\%$ Fe doping and increases linearly to 46 K by $5\,\%$ doping; we infer that a quantum phase transition occurs near the $2.0\,\%$ Fe level. Magnetic fluctuations at the intermediate doping levels are reflected in the linear resistance and an anomalous heat capacity at low temperatures. Imaging and chemical analysis down to the atomic scale show that the Fe dopant is randomly distributed.