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Relaxations as key to the magnetocapacitive effects in the perovskite manganites 



Various perovskite rare-earth manganites are renowned for being multiferroics, i.e. for the simultaneous occurrence of ferromagnetic and ferroelectric order. This is accompanied by strong magnetocapacitive effects where the electrical properties can be influenced by a magnetic field and vice versa. Magnetocapacitance has found tremendous interest in recent years due to its high potential for applications, e.g., in electronic information storage devices. Via a detailed study of various magnetocapacitive manganites with dielectric spectroscopy, we have demonstrated that the strong magnetocapacitive effects, observed for electrical fields E||c, are nearly completely governed by magnetic-state induced changes of relaxation processes. These relaxations show up by a characteristic signature, e.g., in the temperature-dependent dielectric constant (see Figure 1).

relaxation process
Figure 1: ε'(T) of GdMnO3and multiferroic DyMnO3. The steplike decrease of ε' with decreasing temperature indicates a relaxation process. At the magnetic ordering temperatures close to 20 K, significant anomalies show up.

 

A careful analysis revealed strong anomalies of the relaxation parameters, including the relaxation time, at the magnetic phase transitions in these materials and also a significant dependence on magnetic field (Figure 2). It is this variation of the relaxation, which causes the magnetocapacitance in these materials. We ascribe the relaxations to the off-center motion of the manganese ions, which in the multiferroic systems also leads to the ferroelectric ordering.

 relaxation times

Figure 2: Arrhenius plot of the relaxation times of all investigated compounds. The strong anomalies showing up at the magnetic phase transitions explain the magnetocapacitance observed in these materials.

 

To learn more, see:

Relaxations as key to the magnetocapacitive effects in the perovskite manganites
F. Schrettle, P. Lunkenheimer, J. Hemberger, V.Yu. Ivanov, A.A. Mukhin, A.M. Balbashov, and A. Loidl
Phys. Rev. Lett. 102, 207208 (2009)