HfFeGa₂ and HfMnGa₂: Transition-metal-based itinerant ferromagnets with low Curie temperatures

We present a report on the physical properties of the transition-metal- based ferromagnets HfFeGa₂ and HfMnGa₂. The magnetic susceptibility in both displays Curie-Weiss behavior at high temperature that is replaced by the critical susceptibility just above the Curie temperatures, which are 47.9 K in HfFeGa₂ and 25.6 K in HfMnGa₂. The ferromagnetically ordered state has a coercive field of 1700 Oe in HfFeGa ₂ and 320 Oe in HfMnGa₂, with strong anisotropy that largely confines the moments to the b axis. Critical exponents that are derived from neutron diffraction measurements and Arrott plot analyses of the magnetization confirm the mean-field character of the ferromagnetic transitions. Phonons dominate the specific heat at all temperatures, but clear ordering anomalies accompany the onset of ferromagnetic order, as well as an electronic component that is larger in the ordered than paramagnetic states. Both HfFeGa₂ and HfMnGa₂ are metallic, and we observe an anomalous exponent in the temperature-dependent resistivity ρ(T), where ρ(T)-ρ₀=BT5^/3, signaling that the ordered state is a marginal Fermi liquid. Overall, the robustness of ferromagnetic order, the Curie temperatures, and the impact of fluctuations in both HfFeGa₂ and HfMnGa₂ are very similar to those of previously studied ferromagnets, such as MnSi, ZrZn₂, Ni₃Al, and Sc ₃In.