Enhancement of the Curie temperature in single crystalline ferromagnetic LaCrGe$_3$ by electron irradiation-induced disorder

TL;DR

This study demonstrates that electron irradiation-induced disorder unexpectedly increases the Curie temperature in LaCrGe$_3$, suggesting disorder can enhance ferromagnetism by modifying the density of states.

Contribution

It reveals that controlled electron irradiation can increase the Curie temperature in LaCrGe$_3$, providing new insights into disorder effects on itinerant ferromagnets.

Findings

Curie temperature increases from 90 K to nearly 100 K with irradiation

Electron irradiation does not change carrier density significantly

Disorder broadens the density of states peak, increasing $D(E_F)$

Abstract

LaCrGe$_3$ has attracted attention as a potential candidate for studies of quantum phase transitions in a ferromagnetic material. The application of pressure avoids a quantum critical point by developing a new magnetic phase. It was suggested that the disorder may provide an alternative route to a quantum critical point. We used low-temperature 2.5 MeV electron irradiation to induce relatively small amounts of point-like disorder in single crystals of LaCrGe$_3$. Irradiation leads to an increase of the resistivity at all temperatures with some deviation from the Matthiessen rule. Hall effect measurements show that electron irradiation does not cause any detectable change in the carrier density. Unexpectedly, the Curie temperature, $T_{\text{FM}}$, \emph{increases} with the increase of disorder from approximately 90 K in pristine samples up to nearly 100 K in the heavily irradiated sample, with a tendency towards saturation at higher doses. Although the mechanism of this effect is not entirely clear, we conclude that it cannot be caused by effective ``doping" or ``pressure" due to electron irradiation. We suggest that disorder-induced broadening of a sharp peak in the density of states, $D(E)$, situated at $E_p=E_F-0.25$ eV below the Fermi energy, $E_F$, causes an increase in $D(E_F)$, leading to an enhancement of $T_\text{FM}$ in this itinerant ferromagnet.