Enhancement of the Curie temperature in single crystalline ferromagnetic LaCrGe_3 by electron irradiation-induced disorder

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_FM, 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_FM in this itinerant ferromagnet.