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Spin and Charge Ordering in La1-xCaxMnO3 (x = 0.5 and 0.6) Thin Films
V. G. Prokhorov,박정수,K. K. Yu,S. Y. Park,V. A. Komashko,V. L. Svetchnikov,이영백 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
The magnetic and the transport properties of La0.5Ca0.5MnO3 and La0.4Ca0.6MnO3 films with different thickness were investigated. The electron-diffraction study showed that the charge-ordered phase was observed at room temperature for both films. A paramagnetic-to-ferromagnetic (FM) transition at TC 250 K upon cooling in the La0.5Ca0.5MnO3 films and an antiferromagnetic (AFM) phase appeared at TN . 140 K. In the La0.4Ca0.6MnO3 films only the AFM transition was observed at the same temperature. For the La0.5Ca0.5MnO3 film, the FM phase was shown to coexist with the AFM one at low temperatures, and the volume fraction of the FM phase did not exceed 30 %. The magnetoresistive properties of both films could be explained in the framework of the spin-assisted polaron-hopping model.
Structural Clustering and Magnetic Phase Separation in La0.7(Ca1-ySry)0.3MnO3 Thin Films
V. G. Prokhorov,박정수,J.-H. Kang,K. K. Yu,S. Y. Park,V. A. Komashko,V. L. Svetchnikov,이영백 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
The structural, magnetic, and transport properties of the La0.7(Ca1.ySry)0.3MnO3 films prepared by rf-magnetron sputtering have been investigated. At 0.3 y 0.5, both the rhombohedral (R3c) and orthorhombic (Pnma) crystal phases in the form of nanoscale clusters were found to co-exist at room temperature. The observed structural clustering is accompanied by two-stage magnetic and electronic transition, has a metallurgical origin, and is governed by the nonuniform distribution of the lattice strain through the film. The magnetotransport properties of the films can be explained within the framework of a field-dependent activation energy model, considering the spin-dependent trapping of charges and the Weiss-magnetization contribution.
Peculiar Magnetic Dynamics in Amorphous, Nano-Clustered and Self-Organized Nd0.5Sr0.5MnO3 Films
V. G. Prokhorov,이영백,S. Y. Park,현영훈,J. S. Park,G. H. Kim,J.-H. Kang,V. L. Svetchnikov 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3
Amorphous, nano-clustered and self-organized bilayer Nd0.5Sr0.5MnO3 films were prepared by rf magnetron sputtering. The amorphous lm turns out to be a typical paramagnet with free motion of the individual Mn spins. The nano-clustered film manifests magnetic properties, mimicking su- perparamagnetic particles folowing nonclassical magnetic dynamics. The self-organized bilayer film demonstrates a negative exchange bias in spite of the fact that both layers have ferromagnetic ori- gins. The magnetic properties of the films are discussed in detail on the basis of modern theoretical models.
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>