Relaxations as key to the magnetocapacitive effects in the perovskite   manganites
  We present a detailed dielectric study of the relaxation effects that occur in several perovskite rare-earth manganites, including the multiferroics TbMnO3 and DyMnO3. We demonstrate that the strong magnetocapacitive effects, observed for electrical fields E||c, are nearly completely governed by magnetic-state induced changes of the relaxation parameters. The multiferroic materials, which undergo a transition into a spiral magnetic state, show qualitatively different relaxation behavior than those compounds transferring into an A-type antiferromagnetic state. We ascribe the relaxations in both cases to the off-center motion of the manganese ions, which in the multiferroic systems also leads to the ferroelectric ordering. 
F. Schrettle, P. Lunkenheimer, J. Hemberger, V. Yu. Ivanov, A. A.   Mukhin, A. M. Balbashov, and A. Loidl