Abstract
In rare-earth () ferroborates, R() with R = Eu, Gd, and Tb, the magnetoelectric (ME) responses appear to stem from both the antiferromagnetic order of the iron (Fe) spins and the magnetic moments on the ions. We measured the electric polarization () along the axis while rotating a magnetic field () around the axis and found that the target compounds show mutually distinctive -direction dependencies. () (R = Eu) shows an almost constant spontaneous with a slight modulation when is slanted from the axis. The -angle () dependence of the can be described by a formula . As for () and (), they show highly anisotropic dependence of , which characterizes the respective ME responses from their magnetic moments. In certain regions of , the can be described by and for R = Gd and Tb, respectively. We devised a theory for the ME response of the individual magnetic ions in a R() crystal and applied it to these compounds focusing on their local symmetry and their ground-state multiplet structures. The above formulas successfully reproduce the observed results as the summation of from each magnetic subsystem, which in turn enables us to assign the first and second terms to the spontaneous due to a collinear antiferromagnetic ordering of the Fe spins and the ME response of the ion under , respectively. The thermal and -induced evolutions of the magnetic-ion resolved quantitatively agree with the theoretical predictions, ensuring the relevant microscopic ME mechanism for each magnetic ion. The measurement of angular dependence of is particularly useful to decompose the overlapped ME responses into the respective origins in the system with multiple magnetic subsystems.
5 More- Received 1 April 2014
DOI:https://doi.org/10.1103/PhysRevB.89.195126
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