Robust electronic and tunable magnetic states in Sm2 NiMnO6ferromagnetic insulator.

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 unscreeneddnand screeneddn+1L̲(L̲: O 2phole) states. The electronic structure across the Fermi level (EF) exhibits closely spaced Ni 3d, Mn 3dand O 2pstates. 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 2phybridization takes place across the FM transition temperature. Existence of ASD broadens the Ni, Mn 3dspectral 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.

Elucidating the origin of magnetic ordering in ferroelectric BaTiO3- d thin film via electronic structure modification.

With the motive of unraveling the origin of native vacancy induced magnetization in ferroelectric perovskite oxide systems, here we explore the consequences of electronic structure modification in magnetic ordering of oxygen deficient epitaxial BaTiO[Formula: see text] thin films. Our adapted methodology employs state-of-the-art experimental approaches viz. photo-emission, photo-absorption spectroscopies, magnetometric measurements duly combined with first principles based theoretical methods within the frame work of density functional theory (DFT and DFT+U) calculations. Oxygen vacancy (O[Formula: see text]) is observed leading partial population of Ti 3d (t 2g ), which induces defect state in electronic structure near the Fermi level and reduces the band gap. The oxygen deficient BaTiO2.75 film reveals Mott-Hubbard insulator characteristic, in contrast to the band gap insulating nature of the stoichiometric BaTiO3. The observed magnetic ordering is attributed to the asymmetric distribution of spin polarized charge density in the vicinity of O[Formula: see text] site, which originates unequal magnetic moment values at first and second nearest neighboring Ti sites, respectively. Hereby, we present an exclusive method for maneuvering the band gap and on-site electron correlation energy with consequences on magnetic properties of BaTiO[Formula: see text] system, which can open a gateway for designing novel single phase multiferroic system.

Effect of impurities on the long-distance and Zhang-Rice dimers in the quantum magnet Sr14Cu24O41.

We study the effect of impurities on the two types of spin-dimers in the hybrid chain-ladder spin 1/2 quantum magnet Sr[Formula: see text]Cu[Formula: see text]O[Formula: see text]. Four different impurities were used, namely, the non-magnetic Zn (0.0025 and 0.01 per Cu) and Al (0.0025 and 0.01 per Cu), and magnetic Ni (0.0025 and 0.01 per Cu) and Co (0.01, 0.03, 0.05 and 0.1 per Cu). These impurities were doped in high-quality single-crystals synthesized by the floating-zone method. The magnetic susceptibility of pristine Sr[Formula: see text]Cu[Formula: see text]O[Formula: see text] is analyzed rigorously to confirm that at low temperatures ([Formula: see text] K), the 'free' spins in the chains undergo a long-distance dimerization as proposed in a recent study (Sahling et al 2015 Nat. Phys. 11 255). The effect of impurity on these dimers is analyzed by measuring the specific heat down to [Formula: see text] K. We found that even at the lower impurity concentration, the long-distance dimers are significantly severed but the quantum entangled spin dimerized state of the chains persists. On the other hand, the other type of spin dimers that form at relatively higher temperatures via an intervening Zhang-Rice singlet are found to be practically unaffected at the lower impurity concentration; but at 1% doping these dimers are considerably severed. The effect of Co impurity turned out to be most unusual displaying a strongly anisotropic response, and with a dimerization gap that suppresses faster along the chain/ladder direction than perpendicular to it as a function of increasing Co concentration.