S. Kolesnik

Structural and magnetic properties of transition metal substituted ZnO

Structural and magnetic properties have been studied for polycrystalline Zn1−xTMxO, where TM (transition metal ions)=Mn, Fe, and Co. No bulk ferromagnetism was observed for single-phase materials, contrary to the existing theories. Single-phase samples demonstrate paramagnetic Curie–Weiss behavior with antiferromagnetic interactions, similar to other diluted magnetic semiconductors. Nonoptimal synthesis conditions lead to formation of second phases that are responsible for spin-glass behavior {ZnMnO3 impurity for Zn1−xMnxO [S. Kolesnik et al., J. Supercond. 15, 251 (2002)]} or high-temperature ferromagnetic ordering [Co metal for Zn1−xCoxO with the Curie temperature TC>800 K or (Zn,Fe)3O4 for Zn1−xFexO with TC=440 K].Structural and magnetic properties have been studied for polycrystalline Zn1−xTMxO, where TM (transition metal ions)=Mn, Fe, and Co. No bulk ferromagnetism was observed for single-phase materials, contrary to the existing theories. Single-phase samples demonstrate paramagnetic Curie–Weiss behavior with antiferromagnetic interactions, similar to other diluted magnetic semiconductors. Nonoptimal synthesis conditions lead to formation of second phases that are responsible for spin-glass behavior {ZnMnO3 impurity for Zn1−xMnxO [S. Kolesnik et al., J. Supercond. 15, 251 (2002)]} or high-temperature ferromagnetic ordering [Co metal for Zn1−xCoxO with the Curie temperature TC>800 K or (Zn,Fe)3O4 for Zn1−xFexO with TC=440 K].

Absence of room temperature ferromagnetism in bulk Mn-doped ZnO

Structural and magnetic properties have been studied for polycrystalline Zn1−xMnxO (x=0.02,0.03,0.05). Low-temperature (∼500 °C) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 °C. Single-phase samples show paramagnetic Curie–Weiss behavior.

Tolerance factor rules for Sr1−x−yCaxBayMnO3 perovskites

Abstract Synthesis of new perovskite Sr1−x−yCaxBayMnO3−δ compounds is described in detail and dependence of their phase stability and structural distortions on the tolerance factor is discussed. Oxygen contents have been measured over extended temperature and composition ranges. Neutron powder diffraction was used to precisely measure the A–O and Mn–O bond lengths and derive accurate interatomic distances [Ca–O], [Sr–O], [Ba–O], and [Mn–O]. By using these parameters instead of tabulated ionic radii we have derived the functional dependence of the tolerance factor t=t(x,y,T,δ) on composition, temperature, and oxygen content. At a fixed oxygen content, the tolerance factor is an increasing function of temperature as a result of greater thermal expansion of the average 〈A–O〉 bond relative to the 〈Mn–O〉 bond. We find that the stability of the perovskite phase at high temperature is governed, as expected, by the magnitude of tolerance factor (t⩽1) which can be adjusted by controlling the oxygen content 3−δ. This dependence of the tolerance factor on oxygen content and temperature can be utilized to design synthesis conditions for the controlled formation of the new, kinetically stable, perovskite phases.

Origin of Spin-Glass Behavior of Zn1 − xMnxO

Alternating current susceptibility has been studied for polycrystalline Zn1 − xMnxO. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn1 − xMnxO by precipitation of ZnMnO3 in the paramagnetic matrix.

Superconductivity in Ru 1 − x Sr 2 GdCu 2 + x O 8 − y compounds

We report on the properties of new ruthenocuprates

Contribution of oxygen partial pressures investigated over a wide range to SrRuO3 thin-film properties in laser deposition processing

{\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{2}{\mathrm{GdCu}}_{2+x}{\mathrm{O}}_{8\ensuremath{-}y}

Effect of substrate on the atomic structure and physical properties of thermoelectric Ca 3 Co 4 O 9 thin films

(x=0,

Comparison of magnetic and thermoelectric properties of (Nd,Ca)BaCo2O5.5 and (Nd,Ca)CoO3

0.1, 0.2, 0.3, 0.4, and 0.75) that extend the superconductivity found previously in

Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites

{\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}{(T}_{c}=45\mathrm{K})