Magnetic properties of HoFe₆Al₆H hydride: A single-crystal study

Crystal structure and magnetic properties were studied on a single crystal of HoFe₆Al₆H and compared with those of the parent HoFe₆Al compound with a tetragonal crystal structure of the ThMn₁₂₆Al₆ is a ferrimagnet with exact compensation of the Ho and Fe sublattices magnetizations at low temperatures. Both the hydride and the parent compound display a high magnetic anisotropy of the easy-plane type, a noticeable anisotropy exists also within the easy plane with the [110] axis as the easy magnetization direction. The hydrogenation increases slightly (from 10 to 10.45 µ_B) the magnetic moment of the Fe sublattice as a result of volume expansion. It leads to a decompensation of the Fe and Ho sublattices and HoFe₆Al₆H has a spontaneous moment 0.45 µ_B/f.u. The enhancement of the Fe-Fe intra-sublattice exchange interaction results in a higher Curie temperature (T_C) value, 350 K in the hydride as compared to 315 K of HoFe₆Al₆. The Ho-Fe inter-sublattice interaction is also enhanced in the hydride. The molecular field H_mol created on Ho Ions by Fe sublattice is 38 T in HoFe₆Al₆ and 48 T in HoFe₆Al₆H. The inter-sublattice exchange constant n_HoFe is 3.8 T/µ_B and 4.6 T/µ_B, respectively. High-field measurements confirm the enhancement of the Ho-Fe exchange interaction in the hydride found from the temperature dependence of magnetization.