Chang Hoon Sung

Electrical Transport Properties and Magnetoresistance of (1-x)La 0.7 Sr 0.3 MnO 3 /xZnFe 2 O 4 Composites

Abstract The (1- x )La 0.7 Sr 0.3 MnO 3 (LSMO)/ x ZnFe 2 O 4 (ZFO) ( x = 0, 0.01, 0.03, 0.06 and 0.09) composites were prepared bya conventional solid-state reaction m ethod. We investigated the structural properties, m agnetic properties and electricaltransport properties of (1- x )LSMO/ x ZFO composites using X-ray diffraction (XRD), scanning electron microscopy (SEM),field-cooled dc magnetization and magnetoresistance (MR) measurements. The XRD and SEM results indicate that LSMOand ZFO coexist in the composites and the ZFO mostly segregates at the grain boundaries of LSMO, which agreed wellwith the results of the magnetic measurements. The resistivity of the samples increased by the increase of the ZFO dopinglevel. A clear metal-to-insulator (M-I) transition was observed at 360K in pure LSMO. The introduction of ZFO furtherdownshifted the transition temperature (350K-160K) while the transition disappeared in the sample ( x = 0.09) and itpresented insulating/semiconducting behavior in the measured temperature range (100K to 400K). The MR was measuredin the presence of the 10kOe field. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR)was observed in the composites. It was clearly observed that the magnetoresistance effect of x = 0.03 was enhanced at roomtemperature range. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundaryeffect and the intrinsic transport properties together.Key words - (1 x a )L

Magnetic and electrical transport properties on (La0.7Sr0.3MnO3)1−x/(CuFe2O4)x composites

The magnetic and electrical properties of (La0.7Sr0.3MnO3)1?x/(CuFe2O4)x have been investigated. The (La0.7Sr0.3MnO3)1-x/(CuFe2O4)x composites with x = 0, 0.01, 0.03, 0.06 and 0.09 wt.% were prepared by conventional solid state reaction method, respectively. The structures, morphology, magnetic and electrical properties of the samples have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and physical property measurement system (PPMS). The resistance measured as a function of temperature demonstrates that the pure LSMO samples display metal to semiconductor transition. On the other hand, the others indicated semiconductor/insulator behaviors. The MR was measured in an applied magnetic field of 0.5T. The results clearly show that the magnetoresistance (MR) effect is enhanced at a wide temperature range with CuFe2O4 composition. It may be helpful to improve the low-field magnetoresistance (LFMR) under the influence of the spin-polarized tunneling and the spin-dependent scattering.

Electrical and Optical Properties of Ga-doped SnO 2 Thin Films Via Pulsed Laser Deposition

Ga₂O₃-doped SnO₂ thin films were grown by using pulsed laser deposition (PLD) technique on glass substrate. The optical and electrical properties of these films were investigated for different doping concentrations, oxygen partial pressures, substrate temperatures, and film thickness. The films were deposited at different substrate temperatures (room temperature to 600℃). The best opto-electrical properties is shown by the film deposited at substrate temperature of 300℃ with oxygen partial pressure of 80 m Torr and the gallium concentration of 2 wt%. The as obtained lowest resistivity is 9.57 × 10?³ Ω ㎝ with the average transmission of 80% in the visible region and an optical band gap (indirect allowed) of 4.26 eV.

Influence of CoO Phase on Structural, Magnetic and Electrical Properties of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3

The composites of (1-x)La0.7Ca0.3MnO3/xCoO and (1-x)La0.7Sr0.3MnO3/xCoO (x =0 ~ 0.09) were fabricated by conventional solid state reaction method, and their electrical transport and magnetoresistance (MR%) properties were investigated by physical property measurement system (PPMS). The result of x-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicated that no new phase appeared in the composites except manganites matrix and CoO phases. CoO is mainly distributed at the grain boundaries and surfaces of the matrix. The resistivity LCMO and LSMO based composites were measured in the range 90-320K and 90-400K, respectively. The applied magnetic field is 0T and 0.5T. The observed variation of MR with varying Ca and Sr concentration has been qualitatively investigated.