Neutron Scattering Studies of a Multiferroic: Spin-Waves and Magnetic Order in HoMnO₃

Owen Vajk, NCNR

Hexagonal HoMnO₃ is a ferroelectric (T_C=875 K) frustrated antiferromagnet (T_N=72 K) in which these two order parameters are coupled. Our neutron measurements of the spin wave dispersion for the S=2 Mn³⁺ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy D that is 0.093 meV above the spin reorientation transition at 40 K, and 0.126 meV below. For H || c the magnetic phase diagram has been determined, and reveals additional transitions below 8 K where the ferroelectrically displaced Ho³⁺ ions are ordered magnetically.

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