Exchange bias in Sm$ _{2} $NiMnO$ _{6}$/BaTiO$ _{3}$ ferromagnetic-diamagnetic heterostructure thin films

TL;DR

This study demonstrates exchange bias effects in epitaxial Sm$_{2}$NiMnO$_{6}$/BaTiO$_{3}$ heterostructure thin films, revealing the influence of cation disorder, charge transfer, and interface exchange coupling on magnetic properties.

Contribution

It reports the first observation of exchange bias and training effects in SNMO/BTO heterostructures, highlighting the role of cation disorder and interface charge transfer in magnetic behavior.

Findings

Exchange bias depends on cooling field and shows training effects.

Cation disorder introduces local AFM interactions within the FM matrix.

Charge transfer across interfaces can induce magnetism in BTO layers.

Abstract

Exchange bias (EB) shifts are commonly reported for the ferromagnetic (FM)/antiferromagnetic (AFM) bilayer systems. While stoichiometric ordered Sm$_{2}$NiMnO$_{6}$ (SNMO) and BaTiO$_{3}$ (BTO) are known to possesses FM and diamagnetic orderings respectively, here we have demonstrated the cooling field dependent EB and training effects in epitaxial SNMO/BTO/SNMO (SBS) heterostructure thin films. The polarized Raman spectroscopy and magnetometric studies reveal the presence of anti-site cation disorders in background of ordered lattice in SNMO layers, which introduces Ni-O-Ni or Mn-O-Mn local AFM interactions in long range Ni-O-Mn FM ordered host matrix. We have also presented growth direction manipulation of the degree of cation disorders in the SNMO system. Polarization dependent X-ray absorption measurements, duly combined with configuration interaction simulations suggest charge transfer from Ni/Mn 3\textit{d} to Ti 3\textit{d} orbitals through O 2\textit{p} orbitals across the SNMO/BTO (SB) interfaces, which can induce magnetism in the BTO spacer layer. The observed exchange bias in SBS heterostructures is discussed considering the pinning of moments due to exchange coupling at SB (or BTO/SNMO) sandwich interface.