Magnetodielectric anisotropy study of multiferroicity in Y-doped hexagonal HoMnO3

Dielectric measurements are used to characterize magnetic phase transitions in the doped ferroelectric oxides Ho1−xYxMnO3 (x=0–0.8). The focus of this study is on the effects of the magnetic field direction and Y doping on the reentrant T-B-θ phase diagrams below the Néel temperature. The response of Ho sublattice to the applied magnetic field plays a major role in all magnetic phase transitions for Y doping (x=0.0–0.8), consistent with previous results (x=0,0.6,0.8). Two successive Mn spin rotations in the ab plane in the antiferromagnetic state are driven by the exchange interaction with the Ho subsystem, through magnetodielectric coupling. Difference in energy between two ground Mn spin states is correlated with magnetic field induced perturbations in Ho lattice. The coupling between Ho and Mn can be explained by simple geometric relations of uniaxial anisotropy between magnetic field direction and c-axis of hexagonal HoMnO3. The magnetic field anisotropy study is an important step toward the understanding of magnetic and electric phase competition in the diluted Ho 4 f hexagonal system by the nonmagnetic ion yttrium (Y).