Nontrivial temperature dependence of magnetic anisotropy in multiferroic Ba_{2}MnGe_{2}O_{7}

Abstract

We measured the temperature dependences of the static magnetization and the spin excitation in the square-lattice multiferroic Ba_{2}MnGe_{2}O_{7}. An anisotropy gap of the observed low-energy mode is scaled by electric polarization rather than a power of the sublattice moment. Spin-nematic interaction in the effective spin Hamiltonian, which is equivalent to interaction of the electric polarization, is responsible for the easy-axis anisotropy. The nontrivial behavior of the anisotropy gap can be rationalized as change in the hybridized d-p orbital with temperature, leading to the temperature dependence of the spin-nematic interaction.