Browsing by Author "Poh, CK"

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    Re-entrant ferromagnet PrMn2Ge0.8Si1.2: magnetocaloric effect
    (American Institute of Physics, 2009-04-01) Wang, JL; Campbell, SJ; Zeng, R; Poh, CK; Dou, SX; Kennedy, SJ
    The structural and magnetic properties of the re-entrant ferromagnet PrMn2Ge0.8Si1.2 have been investigated by various experimental methods. Similar to the canonical re-entrant ferromagnet SmMn2Ge2, multiple magnetic phase transitions have been detected in PrMn2Ge0.8Si1.2 over the temperature range from 10 to 550 K with re-entrant ferromagnetism occurring around similar to 54 K. The magnetocaloric effect has been measured in terms of the isothermal magnetocaloric entropy change and found to be positive at the re-entrant ferromagnetic transition with a maximum value of around 1.9 J/kg K at 58 K for a magnetic field change of 0-3 T. On the other hand, the entropy change becomes negative (similar to-0.5 J/kg K) at the antiferromagnetic to ferromagnetic transition for the same field change. © 2009, American Institute of Physics
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    Stress/strain induced flux pinning in highly dense MgB2 bulks
    (Institute of Electrical and Electronics Engineers (IEEE), 2009-06-01) Zeng, R; Dou, SX; Lu, L; Li, WX; Poh, CK; Kim, JH; Horvat, J; Shi, DQ; Wang, JL; Munroe, P; Wang, XF; Zheng, RK; Ringer, SP; Rindfleisch, M; Tomsic, M
    We have systematically studied the flux pinning behavior of MgB(2) bulks synthesized by direct diffusion of Mg into pressed pellets of high purity crystalline B powder, with and without mixing with C and SiC nanoparticles, at a reaction temperature of 850 degrees C for 10 hrs. All of the samples showed very high purity and high density, but their microstructure and flux pinning behavior showed significant differences. It was found that the pure MgB(2) agrees with the delta T(c) pinning model, nano-C doped MgB(2) agrees with the delta l pinning model, while the SiC + MgB(2) composite agrees with the delta epsilon pinning model (stress/strain field pinning), since the dominant micro-defects that influence the flux pinning in these three samples are different. © 2009, Institute of Electrical and Electronics Engineers (IEEE)