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V. G. Prokhorov,이영백,조광환,S. Y. Park,V. A. Komashko,V. L. Svetchnikov 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
The magnetic and the transport properties of an amorphous, a partially amorphous and a latticestrained crystalline La0:7Ca0:3MnO3 lm have been investigated. It was shown that the amorphous lm exhibited Pauli paramagnetism with a small ferromagnetic contribution provided by the interfacial crystalline inclusions. A crystalline lm with nano-scale amorphous inclusions demonstrates a superposition of the ferromagnetic (corresponding to the crystalline matrix) and the superparamagnetic (corresponding to the amorphous inclusions) contributions to the magnetization. The tted average size of the superparamagnetic particles, obtained by using a Langevin function, is completely coincident with the size of amorphous clusters represented by high-resolution electronmicroscopy images. The percolating nature of the metal-insulator transition is demonstrated for the lattice-strained crystalline film.
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.
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.
J. H. Lee,이상영,V. A. Komashko 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.5I
Availability of high-temperature superconductor (HTS) films with a critical temperature of 90 K and a surface resistance of 300 μ at 10 GHz and 77 K has enabled the use of superconducting microwave devices for mobile communications. We investigated the microwave surface resistance of YBa2Cu3O7. (YBCO) films grown on CeO2 buffered r-cut sapphire substrates (CbS) and LaAlO3 (LAO) substrates measured at temperatures of 7 . 88 K. The intrinsic surface resistance (Rs) and the penetration depth () of the YBCO films were measured using a rutile-loaded resonator and a sapphire-loaded resonator at the respective resonant frequencies of 8.5 GHz and 19.5 GHz at temperatures below 90 K, for which the effects of the finite film thickness were considered. An Rs of 150 μ was observed at 77 K and 8.5 GHz for the YBCO film on CbS, with the value appearing to be comparable to that of YBCO films on single-crystal LAO substrates. However, at temperatures below 20 K, the RS of the YBCO films on CbS still remained higher than that of the YBCO films on LAO. The reduction in the RS of our YBCO films on CbS near the temperature of 77 K was attributed to a small impurity scattering time (imp) of 0.83 ps, with a much larger imp of 1.2 ps being observed for YBCO on LAO.t[(bt
J.S.Park,C.O.Kim,이영백,V.G.Prokhorov,G.G.Kaminsky,V.A.Komashko,H.C.Ri 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.3
The magnetic and the transport properties of a 20-nm-scale twinned La0:65Ca0:35MnO3 lm have been investigated in a temperature range of 77 - 300 K. The coexistence of ferromagnetic metallic and charge-ordered insulating phases is suggested by the temperature and the current dependences of the resistance at low temperatures. It is shown that thermocycling leads to the formation of a nonequilibrium state in the ensemble of charge-ordered domains and to the appearance of a giant switching in resistance up to 100 %. The experimental results are discussed on the basis of phase separation.
Magnetic and transport properties of La0.8Sr0.2MnO₃/ La0.8Ca0.2MnO₃ bilayer
S. F. Li,J. B. Kim,Y. H. Hyun,Y. P. Lee,V. G. Prokhorov,V. A. Komashko 한국진공학회(ASCT) 2003 Journal of Korean Vacuum Science & Technology Vol.7 No.1
The effects of lattice strain on the magnetic and the transport properties of La_(0.8)Sr_(0.2)MnO₃ films grown on a LaAlO₃ (001) substrate and on a La_(0.8)Ca_(0.2)MnO₃ layer have been studied. It was observed that the metal-insulator and the ferromagnetic transitions turn out to be at higher temperatures for the film deposited on La_(0.8)Ca_(0.2)MnO₃ layer with respect to that on LaAlO₃. The dependence of Curie temperature on the bulk and the Jahn-Teller strains has also been determined.