Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO 3

The complex interplay between the 3d and 4f moments in hexagonal ErMnO 3 is investigated by magnetization, optical second harmonic generation, and neutron-diffraction measurements. We revise the phase diagram and provide a microscopic model for the emergent spin structures, with a special focus on the intermediary phase transitions. Our measurements reveal that the 3d exchange between Mn3 + ions dominates the magnetic symmetry at 10K<T<T N with Mn3 + order according to the Γ 4 representation triggering 4f ordering according to the same representation on the Er3 +(4b) site. Below 10 K the magnetic order is governed by 4f exchange interactions of Er3 + ions on the 2a site. The magnetic Er3 +(2a) order according to the representation Γ 2 induces a magnetic reorientation (Γ 4→Γ 2) at the Er3 +(4b) and the Mn3 + sites. Our findings highlight the fundamentally different roles that Mn3 +, R3 +(2a), and R3 +(4b) magnetism play in establishing the magnetic phase diagram of the hexagonal RMnO 3 system. © 2012 American Physical Society.