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Flux pinning and the paramagnetic Meissner effect in MgB<sub>2</sub> with TiO<sub>2</sub> inclusions
Prokhorov, V G,Svetchnikov, V L,Park, J S,Kim, G H,Lee, Y P,Kang, J-H,Khokhlov, V A,Mikheenko, P IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.4
<P>The mixed-state superconducting properties of bulk MgB<SUB>2</SUB>+2 at.%TiO<SUB>2</SUB>, prepared by the <I>in situ</I> solid state reaction, have been investigated. The high-resolution transmission electron microscopy study reveals that the sample has combined microstructures, consisting of regions with small- and large-size MgB<SUB>2</SUB> grains, and the MgO inclusions. The particular grains are separated by thin TiB<SUB>2</SUB> interlayers along the <I>c</I> axis. Analysis on the mixed-state parameters, such as the upper critical field, the coherence length and the Ginzburg–Landau parameter κ, proves that the MgB<SUB>2</SUB>+2 at.<I>% </I>TiO<SUB>2</SUB> belongs to a high-κ type-II superconductor in the dirty limit. The non-uniformly scaled microstructure results in an unusual (close to the double peak) magnetic field dependence of the pinning force density. The field-cooled temperature dependence of magnetic moment exhibits a transition of the sample to the paramagnetic state at certain applied magnetic fields, which is treated as a manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the basis of modern theoretical approaches.</P>
Flux-Pinning Effects in MgB2 Doped with Nano-Scale TiO2 and SiC Inclusions
이영백,J. S. Park,G. H. Kim,V. L. Svetchnikov,V. G. Prokhorov,J.-H. Kang,V. A. Khokhlov,P. Mikheenko 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3
Bulk MgB2 doped with TiO2 and SiC was prepared by using an in-situ solid state reaction. A high-resolution TEM study revealed that TiO2 doping led to finer grains than doping with SiC one, while small-sized MgO inclusions were presented in both cases. At the same time, the TiO2-doped MgB2 manifested an improved upper critical eld and critical current density over the entire temperature and magnetic eld ranges. We conclude that the observed improvements on superconducting properties are attributable to an enhanced flux pinning by the grain boundaries.