Critical phenomena in itinerant-electron ferromagnet HfFeGa$_2$*

Aiming to study quantum critical behavior in itinerant-electron transition-metal ferromagnets, we have recently been first to characterize the intermetallic compound HfFeGa$_2$. We have found that HfFeGa$_2$ is a ferromagnet with a low ordering temperature and a small ordered magnetic moment. We present extensive magnetization and neutron diffraction studies of single crystals of pristine HfFeGa$_2$. ac-magnetization data indicates the Curie temperature T$_{\mathrm{C}}$ $\sim$ 49 K, and above T$_{\mathrm{C}}$ we find Curie-Weiss behavior with an effective moment of $\sim$ 2.2 $\mu_{\mathrm{B}}$/Fe. HfFeGa$_2$ is ferromagnetic with the ordered magnetic moments parallel to the easy $c$-axis of the orthorhombic crystal structure, and with a zero-temperature spontaneous magnetization of $\sim$ 0.6 $\mu_{\mathrm{B}}$/Fe. By a scaling analysis of magnetization and neutron diffraction data we have determined T$_{\mathrm{C}}$ = 48.3 K as well as the critical exponents $\beta = 0.494$ and $\gamma = 1.21$. Our results indicate HfFeGa$_2$ is comparable to the well-known itinerant ferromagnet ZrZn$_2$.