Robust electronic and tunable magnetic states in Sm2 NiMnO6 ferromagnetic insulator

Abstract

Ferromagnetic insulators (FM-Is) are the materials of interest for the new generation quantum electronic applications. Here, we have investigated the physical observables depicting FM-I ground states in epitaxial Sm2NiMnO6 (SNMO) double perovskite thin films fabricated under different conditions to realize the different level of Ni/Mn anti-site disorders (ASDs). The presence of ASDs immensely influence the characteristic magnetic and anisotropy behaviors in SNMO system by introducing short scale antiferromagnetic interactions in predominant long range FM ordered host matrix. Charge disproportion between cation sites, in the form of Ni2+ + Mn4+ → Ni3+ + Mn3+, causes mixed valency in both Ni and Mn species, which is found insensitive to ASD concentrations. Temperature dependent photo emission, photo absorption measurements duly combined with cluster model configuration interaction simulations, suggest that the eigenstates of Ni and Mn cations can be satisfactorily described as a linear combination of the unscreened d n and screened (: O 2p hole) states. The electronic structure across the Fermi level (E F) exhibits closely spaced Ni 3d, Mn 3d and O 2p states. From occupied and unoccupied bands, estimated values of the Coulomb repulsion energy (U) and ligand to metal charge transfer energy (Δ), indicate charge transfer insulating nature, where remarkable modification in Ni/Mn 3d—O 2p hybridization takes place across the FM transition temperature. Existence of ASD broadens the Ni, Mn 3d spectral features, whereas the spectral positions are found to be unaltered. Hereby, present work demonstrates SNMO thin film as a FM-I system, where the FM state can be tuned by manipulating ASD in the crystal structure, while the I state remains intact.