Role of the rare earth in lattice and magnetic coupling in multiferroic h−HoMnO3

Abstract

We used Raman scattering to study the lattice and magnetic excitations in the hexagonal HoMnO3 single crystals. The E2 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 a-b plane and modulates the Mn-O-Mn bond angles in a-b plane and 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 TN showing that the role of the rare earth ions can not 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.

Spin reorientation behaviour and dielectric properties of Fe-doped h-HoMnO3

“…This leads to the formation of 2D triangular lattices in the a-b plane composed of Mn 3+ spins, leading to frustration in these systems. However, as compared to h-RMnO 3 with a non-magnetic R 3+ ion, the value of frustration parameter, f (= θ CW /T N ; θ CW is the Curie-Weiss (C-W) temperature) [11], is low in compounds with a magnetic R ion [12] due to the presence of R-Mn interactions along the c-axis [13].The coupling between Ho and Mn moments has been confirmed earlier by both theory [14] and experiments [15][16][17]. More recent reports [18] point towards the coupling between the Mn spin waves and Ho crystal field excitations.…”