Crystal and Magnetic Structure of Polar Oxide HoCrWO$_6$

Polar magnetic oxide HoCrWO$_6$ is synthesized and its crystal structure, magnetic structure, and thermodynamic properties are investigated. HoCrWO$_6$ forms the polar crystal structure (space group Pna2$_1$ (#33)) due to the cation ordering of W$^{6+}$ and Cr$^{3+}$. There is an antiferromagnetic transition at TN = 24.5 K along with the magnetic entropy change (~5 J.Kg.$^{-1}$K$^{-1}$ at 70 kOe). Neutron diffraction measurement indicates that both Cr and Ho sublattices are ordered with the moment of 2.32(5)$\mu_B$ and 8.7(4)$\mu_B$ at 2 K, respectively. While Cr forms A-type collinear antiferromagnetic (AFM) structure with magnetic moment along the $b$ axis, Ho sublattice orders in a non-coplanar AFM arrangement. A comparison with isostructural DyFeWO$_6$ and DyCrWO$_6$ indicates that the magnetic structure of this family of compounds is controlled by the presence or absence of eg electrons in the transition metal sublattice.