Room-temperature surface multiferroicity in Y$_2$NiMnO$_6$ nanorods

TL;DR

This study demonstrates room-temperature multiferroicity in Y$_2$NiMnO$_6$ nanorods caused by surface defects, showing strong magnetoelectric coupling at room temperature, unlike the bulk material which only exhibits multiferroicity below 70 K.

Contribution

It reveals that surface defects in nanorods can induce room-temperature multiferroicity and magnetoelectric coupling, a phenomenon not observed in the bulk form of the material.

Findings

Surface ferromagnetism of 0.005 emu/g at 50 kOe

Ferroelectric polarization of ~2 nC/cm$^2$

80% decrease in polarization under 15 kOe magnetic field

Abstract

We report observation of surface-defect-induced room temperature multiferroicity - surface ferromagnetism ($M_S$ at 50 kOe $\sim$0.005 emu/g), ferroelectricity ($P_R$ $\sim$2 nC/cm$^2$), and significantly large magnetoelectric coupling (decrease in $P_R$ by $\sim$80\% under $\sim$15 kOe field) - in nanorods (diameter $\sim$100 nm) of double perovskite Y$_2$NiMnO$_6$ compound. In bulk form, this system exhibits multiferroicity only below its magnetic transition temperature $T_N$ $\approx$ 70 K. On the other hand, the oxygen vacancies, formed at the surface region (thickness $\sim$10 nm) of the nanorods, yield long-range magnetic order as well as ferroelectricity via Dzyloshinskii-Moriya exchange coupling interactions with strong Rashba spin-orbit coupling. Sharp drop in $P_R$ under magnetic field indicates strong cross-coupling between magnetism and ferroelectricity as well. Observation of room temperature magnetoelectric coupling in nanoscale for a compound which, in bulk form, exhibits multiferroicity only below 70 K underscores an alternative pathway for inducing magnetoelectric multiferroicity via surface defects and, thus, in line with magnetoelectric property observed, for example, in domain walls or boundaries or interfaces of heteroepitaxially grown thin films which do not exhibit such features in their bulk.