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Abstract: We present detailed magnetization and magneto-transport studies on the title compound SmCoAsO. In a recent paper we reported (Awana et al., 2010 ) the complex magnetism of this compound. SmCoAsO undergoes successive paramagnetic (PM)–ferro-magnetic (FM)–anti-ferro-magnetic (AFM) transitions with decrease in temperature. This is mainly driven via the c-direction interaction of Sm4f (SmO layer) spins with adjacent (CoAs layer) ordered Co3d spins. In this article we present an evidence of kinetic arrest for FM–AFM transition. The isothermal magnetization (MH) loops for SmCoAsO exhibited the meta-magnetic transitions at 6, 8 and 10K at around 80, 60 and 50kOe fields, respectively, with characteristic hysteresis shoulders along with the non-zero moment at the origin, thus suggesting the possibility of kinetic arrest. Suggested kinetic arrest is further evident in zero field-cooled (ZFC) and field-cooled (FC) hysteresis under high fields of up to 140kOe magnetization (MT) and the magneto-transport measurements R(T)H during FM–AFM transition. The time dependent moment experiments exhibited very small (∼2–3%) increase of the same below 20kOe and decrease for 30kOe at 15K. [Copyright &y& Elsevier]

Abstract: We report the synthesis and magnetization of Sr2RuREO6 (RE/Ru-211O6) with RE=Gd and Eu. Both Gd and Eu/Ru-211O6 are formed in distorted perovskite-type single phase with monoclinic P21/n space group. Magnetization (M/T) measurements exhibited antiferromagnetic ordering of Ru moments for both Gd and Eu compounds at a T N of around 30K due to super-exchange Ru–O–O–Ru interaction. Interestingly enough, detailed M/H plots of Gd/Ru-211O6 exhibited the development of a ferromagnetic (FM) component at 20K. Furthermore, below 10K, the FM component disappears, and rather spin freezing field (H SF) of around 1000Oe is seen at 5K. In case of Eu/Ru-211O6, the basic antiferromagnetic ordering of Ru moments remains invariantly down to 5K, and the appearance of the FM component is not seen. It seems that the high magnetic moment of 8μ B for Gd3+ influences the anti ferromagnetic (AFM) ordering of Ru in case of Gd/Ru-211O6. [Copyright &y& Elsevier]

Abstract: The magnetic and magnetocaloric properties of polycrystalline La0.70(Ca0.30−x Sr x )MnO3:Ag 10% manganite have been investigated. All compositions are crystallized in single phase orthorhombic Pbnm space group. Both, the insulator–metal transition temperature (T IM ) and Curie temperature (T c ) are observed at 298K for x=0.10 composition. Though both T IM and T c are nearly unchanged with Ag addition, the MR is increased. The MR at 300K is found to be as large as 31% with magnetic field change of 1T, whereas it reaches up to 49% at magnetic field of 3T for the La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample. The maximum entropy change (ΔS Mmax ) at near its T c (300.5K) is 7.6Jkg−1 K−1 upon the magnetic field change of 5T. The La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample having good MR (31%1T, 49%3T) and reasonable change in magnetic entropy (7.6Jkg−1.K−1, 5T) at 300K can be a potential magnetic refrigerant material at ambient temperatures. [Copyright &y& Elsevier]

Abstract: The structural magnetic and magneto-transport properties of double perovskite system Ba2− x Sr x FeMoO6 (0⩽x⩽1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe–Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba2FeMoO6 exhibits saturation magnetic moment value of 3.54μB/f.u. at 85K in a magnetic field of 6000Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73μB/f.u. and MR value of 7.08% (1T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail. [Copyright &y& Elsevier]