Mapping the magnetic state as a function of anti-site disorder in Sm$ _{2} $NiMnO$ _{6} $ double perovskite thin films

TL;DR

This study maps how anti-site disorder in Sm$_{2}$NiMnO$_{6}$ thin films affects their magnetic and electronic properties, revealing how defect control can tune magnetic phases and anisotropy.

Contribution

It provides a detailed analysis of the relationship between anti-site disorder and magnetic/electronic states in double perovskite thin films, with controlled defect engineering.

Findings

Disorder affects magnetic transition temperature and saturation magnetization.

Increased ASD reduces magnetic anisotropy and enhances moment pinning.

Charge disproportionation signatures are independent of ASD levels.

Abstract

The predictability of any characteristic functional aspect in a double perovskite system has always been compromised by its strong dependence over the inevitably present anti-site disorders (ASD). Here, we aim to precisely map the quantitative and qualitative nature of ASD with the corresponding modifications in observables describing the magnetic and electronic state in epitaxial Sm$ _{2} $NiMnO$ _{6} $ (SNMO) double perovskite thin films. The concentration and distribution patterns of ASD are effectively controlled by optimizing growth conditions and estimated on both local and global scales utilizing extended X-ray absorption fine structure and bulk magnetometry. Depending upon the defect densities, the nature of disorder distribution can vary from homogeneous to partially segregated patches. Primarily, the effect of varying B-site cationic arrangement in SNMO is reflected as the competition of long range ferromagnetic (FM) and short scale antiferromagnetic (AFM) interactions originated from ordered Ni-O-Mn and disordered Ni-O-Ni or Mn-O-Mn bonds, respectively, which leads to systematic shift in magnetic transition temperature and drastic drop in saturation magnetization. In addition, we have observed that the gradual increment in density of ASD leads to significant deviation from uniaxial anisotropy character, reduction in anisotropy energy and enhancement of moment pinning efficiency. However, the observed signatures of $ Ni^{2+}+Mn^{4+} \longrightarrow Ni^{3+}+Mn^{3+} $ charge disproportionation is found to be independent of cation disorder densities. This work serves as a basic route-map to tune the characteristic magnetic anisotropy, magnetic phase transitions, and magnetization reversal mechanism by controlling ASD in a general double perovskite system.