Robust electronic and tunable magnetic states in Sm₂ NiMnO₆ ferromagnetic insulator

Abstract

Ferromagnetic insulators (FM-Is) are the materials of interest for 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 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 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 dn and screened dn+1L (L: O 2p hole) states. The electronic structure across the Fermi level (EF ) 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 (∆), 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 spectral positions are found to be unaltered. Hereby, present work demonstrates SNMO thin film as a FM-I system, where FM state can be tuned by manipulating ASD in the crystal structure, while I state remains intact.

Existence of inter coupled structural, electronic and magnetic states in Sm$ _{2} $NiMnO$ _{6} $ double perovskite

“…Therefore, EXAFS modeling confirms the presence of Ni/Mn cation ordered and disordered structures in SNMO lattice. Such local anti-site disorder lefts its imprint in magnetization behaviors by introducing short scale antiferromagnetic interaction in background of long range ferromagnetic ordered SNMO lattice [4,5,6].…”

“…In materials science there has been always a quest for the strong correlation between charge, spin and lattice degrees of freedom to have additional control over functional aspects of the system [1]. Double perovskites with Ni and Mn as B-site cations A 2 NiMnO 6 (ANMO), have huge potential in new generation quantum electronics owing to rare tunable ferromagnetic insulating ground state [2,3,4,5,6]. In a previous theoretical study it is predicted that LNMO (A=La) holds magnetic order dependent electronic properties [7].…”

“…Whereas, a random occupation between Ni/Mn ions are formed for orthorhombic case. However in practical crystal system, completely ordered or disordered situation is difficult to achieve due to comparable ionic sizes of Ni and Mn species [4,5,6]. Even in highly ordered system, some fraction of disorder is present owing to anti-phase boundary formation [20].…”

“…Even in highly ordered system, some fraction of disorder is present owing to anti-phase boundary formation [20]. Different ordered and disordered coordinations have drastic role in stabilizing the magnetic phase of the system [4,5,6]. The temperature effect on local and global crystal environments of ANMO is yet to be explored.…”

Magnetic properties of disordered polycrystalline bulk Sm$ _{2} $NiMnO$ _{6} $ double perovskite

“…[7,8,9,10]. The presence of anti-site disorder introduces further complexity in the phase diagram of DP structures [11,12,13]. In the present work, we aim to investigate the structural, magnetic and electronic properties of so far un-explored B-site disordered Sm 2 NiMnO 6 (SNMO) double perovskite oxide.…”