Meier, D.; Ryll, H.; Kiefer, K.; Klemke, B.; Hoffmann, J.-U.; Ramesh, R.; Fiebig, M.: Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO3. Physical Review B 86 (2012), p. 184415/1-8
10.1103/PhysRevB.86.184415
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Abstract:
The complex interplay between the 3d and 4f moments in hexagonal ErMnO3 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 T between 10 K and TN with Mn3+ order according to the Gamma4 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 Gamma2 induces a magnetic reorientation (Gamma4-->Gamma2) 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 RMnO3 system.