Clastin I. Sathish

Superconductivity suppression of Ba0.5K0.5Fe2−2xM2xAs2 single crystals by substitution of transition metal (M = Mn, Ru, Co, Ni, Cu, and Zn)

We investigated the doping effects of magnetic and nonmagnetic impurities on the single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu and Zn) superconductors. The superconductivity indicates robustly against impurity of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However, the present Tc suppression rate of both magnetic and nonmagnetic impurities remains much lower than what was expected for the s\pm-wave model. The temperature dependence of resistivity data is observed an obvious low-T upturn for the crystals doped with high-level impurity, which is due to the occurrence of localization. Thus, the relatively weak Tc suppression effect from Mn, Co, Ni, Cu, and Zn are considered as a result of localization rather than pair-breaking effect in s\pm-wave model.

High-temperature ferrimagnetism driven by lattice distortion in double perovskite Ca2FeOsO6.

5d and 3d hybrid solid-state oxide Ca2FeOsO6 crystallizes into an ordered double-perovskite structure with a space group of P2₁/n with high-pressures and temperatures. Ca2FeOsO6 presents a long-range ferrimagnetic transition at a temperature of ~320 K (T(c)) and is not a band insulator, but is electrically insulating like the recently discovered Sr2CrOsO6 (T(c) ~725 K). The electronic stat of Ca2FeOsO6 is adjacent to a half-metallic state as well as that of Sr2CrOsO6. In addition, the high-T(c) ferrimagnetism was driven by lattice distortion, which was observed for the first time among double-perovskite oxides and represents complex interplays between spins and orbitals. Unlike conventional ferrite and garnet, the interplays likely play a pivotal role of the ferrimagnetism. A new class of 5d-3d hybrid ferrimagnetic insulators with high-T(c) is established to develop practically and scientifically useful spintronic materials.

Superconductivity in Bismuth Oxysulfide Bi4O4S3

Bismuth oxysulfide Bi4O4S3, which has recently been claimed to be an exotic superconductor (Tc = 4.5 K), was investigated by magnetic susceptibility and electrical resistivity measurements as well as by electron probe microanalysis. Single-phase Bi4O4S3 was successfully prepared by a high-pressure method, and its lattice parameters and normal-state resistivity, as well as the density of states at the Fermi level, were found to be comparable to those determined earlier. However, the observed superconductivity was most likely impurity-driven, strictly contradictory to the observations in ongoing experiments. The present results indicate that the superconductivity of Bi4O4S3 does not truly reflect the bulk nature of the BiS2 layered phase, regardless of the manner in which Bi4O4S3 is synthesized. We discuss possible superconducting impurities.

High pressure synthesis, crystal structure, and magnetic properties of the double-perovskite Sr2FeOsO6

The double-perovskite compound Sr2FeOsO6 was synthesized using a high pressure, high-temperature method. The crystal structure, electrical resistivity, and magnetic properties of Sr2FeOsO6 were investigated. It was found that Sr2FeOsO6 crystallizes in a partially disordered structure (I4/m) and exhibits semiconductor-like behavior and an antiferromagnetic transition at 78 K.

Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15).

The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.

Carbon-Induced Ferromagnetism in the Antiferromagnetic Metallic Host Material Mn3ZnN.

Carbon-for-nitrogen substitution (51 at% at most) was achieved in the antiferromagnetic metallic host material Mn(3)ZnN. The various carbon-doped compounds were studied using synchrotron X-ray diffraction, and their electrical resistivities, specific heats, and degrees of magnetization were measured for temperatures of 2-400 K. The sharp antiferromagnetic-to-paramagnetic transition of the host material at 185 K broadened markedly as the carbon content was increased, and a significant ferromagnetic character was found to coexist with the antiferromagnetism when the carbon concentration exceeded 27 at%. This critical magnetic behavior is likely in part due to the increase in the density of states at the Fermi level and the increase in the distance between neighboring Mn atoms. The exact mechanism responsible for the induction of the complicated magnetic state could not be determined. However, the results demonstrate clearly that the chemical tuning of the X site in antiperovskite Mn(3)AX materials is as useful as that of the A and Mn sites and can be used to develop the properties of these materials for practical applications.

Unusual magnetic hysteresis and the weakened transition behavior induced by Sn substitution in Mn3SbN

Substitution of Sb with Sn was achieved in ferrimagnetic antiperovskite Mn3SbN. The experimental results indicate that with an increase in Sn concentration, the magnetization continuously decreases and the crystal structure of Mn3Sb1-xSnxN changes from tetragonal to cubic phase at around x of 0.8. In the doping series, step-like anomaly in the isothermal magnetization was found and this behavior was highlighted at x = 0.4. The anomaly could be attributed to the magnetic frustration, resulting from competition between the multiple spin configurations in the antiperovskite lattice. Meantime, Hc of 18 kOe was observed at x = 0.3, which is probably the highest among those of manganese antiperovskite materials reported so far. With increasing Sn content, the abrupt change of resistivity and the sharp peak of heat capacity in Mn3SbN were gradually weakened. The crystal structure refinements indicate the weakened change at the magnetic transition is close related to the change of c/a ratio variation from tetrago...

Thermodynamic, Electromagnetic, and Lattice Properties of Antiperovskite Mn3SbN

The physical properties of polycrystalline Mn3SbN were investigated using measurements of the magnetic, calorimetric, and electronic transport properties. At room temperature, the phase crystallizes in a tetragonal structure with symmetry. A remarkably sharp peak in the heat capacity versus temperature curve was found near 353 K. The peak reaches 723 J mol−1 K−1 at its highest, which corresponds to a transition entropy of 10.2 J mol−1 K−1. The majority of the large entropy change appears to be due to lattice distortion from the high-temperature cubic structure to the room-temperature tetragonal structure and the accompanying Ferrimagnetic transition.

Magnetic and electrical properties of antiperovskite Mn3InN synthesized by a high-pressure method

Mn3InN antiperovskite is synthesized under high-pressure conditions, followed by measurements of magnetic susceptibility, isothermal magnetization, electrical resistivity, and specific heat. Multiple magnetic interactions are observed between 2 K and 400 K: the paramagnetic state turns to an antiferromagnetic state at 300 K on cooling, and a weak ferromagnetic contribution appears at 175 K by further cooling. Below 50 K, an enhanced ferromagnetic contribution is obvious. Although a long-range antiferromagnetic order is clearly established at room temperature, the material retains a good metallic conduction over a wide temperature range (the Sommerfeld coefficient is 43.3 mJ mol−1 K−2), suggesting a possible use of the material in spintronics applications.

Crystal Structure and Magnetic Properties of Sr2LiOsO6

In recent years, 5d oxides have received considerable attention because of their distinctive features such as unusual superconductivity in KOs2O6 [1], noticeable metal-to-insulator transition in NaOsO3 [2], unusual Mott-insulating state in Sr2IrO4 [3], and unusually high Curie temperature of ~725 K in Sr2CrOsO6 [4]. In particular, osmium-containing oxides have been investigated intensively, and recently, the structure and magnetic properties of Ba2MOsO6 (M = Li, Na, Ca) [5,6], Sr2MOsO6 (M = Fe and Cr) [4,7], and Ca3OsO6 [8] have been studied. We synthesized Sr2LiOsO6 to search for a 5d feature that is distinguishable from 3d features. An early study on Sr2LiOsO6 by Sleight et al. [9] found that it is a cubic phase; however, the detailed crystal structure was not revealed. In the current study, we found that Sr2LiOsO6 crystallizes in a tetragonal double-perovskite structure at room temperature. The refined crystal structure and magnetic properties are reported here.