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RISS 인기검색어
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- 저자 : I. Pasuk (검색결과 3 건)
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V. Mihalache,M. Cernea,I. Pasuk 한국물리학회 2017 Current Applied Physics Vol.17 No.8
The magnetic properties, in the 5 Ke350 K temperature range, were investigated in relationship with the structure and morphology of Zn1xFexO (x ¼ 0, 0.01, 0.03) powders prepared by hydrothermal route. The magnetization measurements reveal that all powders are ferromagnetic at room temperature, with Curie temperature Tc, higher than 350 K. The coercivity Hc takes values between 58 Oe and 107 Oe at 300 K and, between 217 Oe and 613 Oe at 5 K. The weak magnetization of the un-doped ZnO powder is temperature independent and was associated with the high surface to volume ratio of the powder particles (or the number of surface defects). The saturation magnetization Ms was substantially enhanced (up to a factor of about 20 at 300 K and of about 200 at 5 K) at all temperatures as Fe concentration increased, in spite of reduction of the surface to volume ratio of the powder particles. The Hc vs. T and FC/ ZFC curves for the un-doped ZnO show typical ferromagnetic behavior, whereas for the Fe doped powders exhibit RudermaneKitteleKasuyaeYosida (RKKY) - like and spin-glass-like behavior. The observed magnetic phenomena in Fe doped ZnO can be explained on the basis of “donor defects concentration e magnetic cations concentration” phase diagram for dilute magnetic semiconductors.
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Structural, electric and pyroelectric properties of up and down graded PZT multilayers
M. Botea,L. Hrib,I. Pasuk,A. Iuga,L. Trupina,R. Negrea,N. Becherescu,L. Pintilie 한국물리학회 2019 Current Applied Physics Vol.19 No.7
Multi-layered structures, composed of thin films from materials with different compositions or physical properties, represents a way to obtain enhanced properties or even new functionalities. In this work, lead zirconate titanate PbZrxTi1-xO3 (PZT; x=0.20, 0.52, 0.80) multilayers were grown by pulsed laser deposition (PLD) on a single crystal strontium titanate (SrTiO3, STO) substrate, using a strontium ruthenate (SrRuO3, SRO) film as buffer layer for epitaxial growth, and also as back electrode. Up and down multi-layers were grown and their physical and structural properties were compared, up being the structure in which Zr concentration was varied from 20% near the STO substrate to 80% at the surface, while down is for the structure in which the Zr concentration starts with 80% near the substrate and ends with 20% at the surface. It was found that the electric and pyroelectric properties of the two graded structures are significantly different. The up structure presents electric properties that are comparable with those of single composition PZT films while the properties of the down structure are deteriorated, especially in terms of the leakage current magnitude. Pyroelectric signal could be measured only for the up structure. These differences were attributed to larger density of structural defects in the down structure compared to the up one. This is due to the different growth sequence: up structure starts with tetragonal PZT on cubic substrate (lower lattice mismatch, 1.1%) while down structure starts with rhombohedral PZT on cubic substrate (larger lattice mismatch, almost 5%).
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B4C in ex-situ spark plasma sintered MgB2
M. Burdusel,G. Aldica,S. Popa,M. Enculescu,V. Mihalache,A. Kuncser,I. Pasuk,P. Badica 한국물리학회 2015 Current Applied Physics Vol.15 No.10
Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C)x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 ℃ for 3 min. The average particle size of B4C raw powder was relatively high of 4 mm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density Jc at high magnetic fields and of the irreversibility field Hirr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a Jc of 100 A/cm2 is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions.
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