Magnetization and magnetic phases in metallic and semiconducting Ho_xCa_1-xMnO₃

Abstract

We have measured the magnetization, susceptibility, specific resistance, X-ray and neutron diffraction data of the series Ho_xCa_l-xMnO₃ (x≤0.5; step width Δx = 0.1 or less). The compounds analyzed have distorted perovskite structures: they are orthorhombic for 0≤x≤0.13, and have an orthorhombic to monoclinic phase transition for 0.13≤x≤0.33. Ho ions are paramagnetic for 4 K≤T≤300 K. Their magnetization and susceptibility at low temperatures are, however, reduced from what one expects for free ions. We calculate a crystal field correction M_Ho(T, H) and χ_Ho(T). The resulting data for Mn show a reduced magnetic moment (x≥0.2) and a ferromagnetic phase at x = 0.1 ± 0.05 with ordering temperatures T_N/T_C ≈ 110 K. These results show that (Ho_xCa_1-x)MnO₃ belongs to the family of the giant magnetoresistance compounds (La_xCa_1-x)MnO₃ with, however, the ferromagnetic phase occuring at x = 0.1 as compared to x = 0.67 in the La-compound.