Role of the rare earth in lattice and magnetic coupling in multiferroic h−HoMnO3
Résumé
We used Raman scattering to study the lattice and magnetic excitations in the hexagonal HoMnO 3 single crystals. The E 2 phonon mode at 237 cm −1 is affected by the magnetic order. This mode is related to the displacement of Mn and O ions in the a-b plane and modulates the Mn-O-Mn bond angles in the a-b plane and in the in-plane Mn-Mn superexchange interaction. The mode at 269 cm −1 associated to the displacement of the apical Ho 3+ ions along the c direction presents an abrupt change of slope at T N , showing that the role of the rare-earth ions cannot be neglected in the magnetic transition. We have identified magnon and crystal-field excitations. The temperature dependence of the magnetic excitations has been compared to the Mn and Ho moment and indicates that the exchange-interaction pattern between Mn and Ho atoms drives the uniaxial anisotropy gap above the Mn-spin-rotation transition.
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