Glassy dielectric response in Tb₂NiMnO₆ double perovskite with similarities to a Griffiths phase

¹ Department of Physics, Indian Institute of Science - Bangalore 560012, India
² Jülich Center for Neutron Sciences and Peter Grünberg Institute, JARA- FIT, Forschungszentrum Jülich GmbH - 52425 Jülich, Germany
³ Center for Soft Mater Research - Jalahalli, Bangalore 560013, India

Received: 25 November 2013
Accepted: 18 December 2013

Abstract

Results of frequency-dependent and temperature-dependent dielectric measurements performed on the double-perovskite Tb₂NiMnO₆ are presented. The real and imaginary parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from the bulk, grain boundaries and the sample-electrode interfaces, respectively. The and are successfully simulated by a RC circuit model. The complex plane of impedance, , is simulated using a series network with a resistor R and a constant phase element. Through the analysis of using the modified Debye model, two different relaxation time regimes separated by a characteristic temperature, , are identified. The temperature variation of R and C corresponding to the bulk and the parameter α from modified Debye fit lend support to this hypothesis. Interestingly, the compares with the Griffiths temperature for this compound observed in magnetic measurements. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is markedly clear. We assume that the observed features have their origin in the polar nanoregions which originate from the inherent cationic defect structure of double perovskites.