Ferromagnetism and the Effect of Free Charge Carriers on Electric Polarization in Y_2NiMnO_6 Double Perovskite

TL;DR

This study investigates the magnetic and dielectric properties of Y_2NiMnO_6, revealing ferromagnetism at 81 K and showing that electric polarization arises from free charge carriers, not spontaneous ferroelectricity.

Contribution

It provides detailed structural, magnetic, and dielectric analysis of Y_2NiMnO_6, clarifying the origin of electric polarization as due to free charge carriers rather than intrinsic ferroelectricity.

Findings

Ferromagnetic transition at 81 K confirmed by neutron diffraction.

Dielectric anomaly coincides with ferromagnetic transition.

Pyrocurrent results indicate charge carrier re-orientation, not spontaneous polarization.

Abstract

The double perovskite Y_2NiMnO_6 displays ferromagnetic transition at Tc = 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (M_s) and also, validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P 21/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of frequency dependent dielectric constant and equivalent circuit analysis of impedance data takes into account the bulk contribution to total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T_c). Pyrocurrent measurements register a current flow with onset near Tc and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to re-orientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material