Tunable Competition and Possible Coexistence of Magneto-Electric Phases in A Charge Ordered Manganite

Abstract

The magnetoelectric (ME) effect, i.e., cross control of magnetization (electric polarization) by an external electric (magnetic) field, may introduce a new design principle for novel spin devices. However, it has been a long-standing challenge to enhance the magnetoelectric effect. There are two known magnetoelectric effects: a conventional linear magnetoelectric effect in a centrosymmetry-broken magnet and a recently explored nonlinear magnetoelectric effect associated with a magnetic phase transition. To enhance the ME signal, effective control of a phase competition has recently been revealed as a promising approach. Here, we report the magnetic field control of the distinct ME phases in a charge ordered magnet Pr0.75Na0.25MnO3, in which an antiferromagnetic (AFM) phase is competing with a ferromagnetic (FM) phase. Charge ordered magnetic compounds are a far more promising class of materials with potentially large magnetoelectric coupling. The material is prepared by wet chemical route at low sintering time and temperature in order to maintain the Na stoichiometry. The phase purity and structure is well studied through different techniques. The temperature evolution of resistivity and dielectric shows anomaly at charge ordering (CO) transition. With rise in temperature raises the dielectric parameter upto CO and then decreases. The rise in this region is probably due to the formation of polar regions. However, at different frequency, the slope change in dielectric permittivity and peak in loss tangent are uncorrelated signifies this system to be a relaxor. The magnetic field dependent dielectric behavior is highly correlated but in contrast to their resistivity. Surprisingly, the dielectric parameter follows the magnetic signal. The variation of dielectric permittivity with field is intrinsically associated with the coexisting phases of contrasting order. However, the ground state of this system is proved to be ferromagnetic. Using suitably experimental protocol the magnetic phases as well as electronic phases can be tuned effectively at low magnetic field vis-à-vis to enhance the ME signal. Moreover, the FM in the proximity of AFM phase enhance the functionality of this materials with a several order in the ME parameter. The apparent change in ME signal in accordance with macroscopic phase competition are modelled through Maxwell’s dynamical theory. We envisage that this short of studies will renders valuable information for other materials which shows similar behavior.