Neutron-scattering studies of magnetism in multiferroic HoMnO3 (invited).

Hexagonal HoMnO3 is a frustrated antiferromagnet (TN=72 K) ferroelectric (TC=875 K) with a rich magnetic phase diagram consisting of multiple temperature- and field-dependent phases. Previously observed anomalies in the dielectric constant at magnetic phase transitions indicate strong coupling between the ferroelectricity and magnetism. Neutron-diffraction measurements in a magnetic field reveal new intermediate-field phases at low temperatures. Inelastic neutron-scattering measurements are used to establish the primary magnetic interactions and demonstrate that the spin dynamics in HoMnO3 are well described by a simple two-dimensional nearest-neighbor Heisenberg antiferromagnetic exchange J=2.44 meV and a temperature-dependent anisotropy D. [ABSTRACT FROM AUTHOR]