Ac susceptibility of Ho (Fe,CO)11Ti compounds and their hydrides

Abstract The structural characterization and ac susceptibility behavior of polycrystalline samples of HoFe 11− x Co x TiH y ( x =1, 2, 4, 6, 7, 9, 11 and y =0, 1) intermetallics are investigated. All compounds crystallize in tetragonal ThMn 12 -type structure. The replacement of Fe by Co causes the lattice constants to decrease, while hydrogen insertion leads to cell volume expansion. A spin-reorientation (SR) transition from a uniaxial to cone/planar structure is observed for the HoFe 11− x Co x Ti compounds of higher Co content ( x >7). By hydrogenation, SR transition appears in all samples due to relative reinforcement of Ho contribution to anisotropy. T SR values increase by Co-content because of the preferential substitution of Fe by Co atoms and consequently, concentration-dependence of contribution of transition metal sublattice to anisotropy, as well as that of Ho. The concentration-dependence of magnetization direction and hydrogen-induced SR in the studied samples are discussed in the framework of two-magnetic sublattice model by bearing in mind the temperature-dependent competition of their anisotropies and dependence of magnetic anisotropy on crystal field interactions.