• Journal of the Korean Magnetics Society
• /
• v.14 no.1
• /
• pp.38-44
• /
• 2004

The iron doped colossal magnetoresistance materials with La-Ba-Mn-O perovskites structure have been synthesized by chemical reaction of sol-gel methods. Their crystallographic and magnetic properties have been studied with x-ray diffraction, VSM, RBS, Mossbauer spectroscopy, and magnetoresistance measurements. The crystal structure of the La$\_$0.67/Ba$\_$0.33/Mn$\_$0.99/Fe$\_$0.01/ $O_3$ at room temperature was determined to be orthorhombic of Pnma. The lattice parameters a$\_$0/ and c$\_$0/ increased gradually, but b$\_$0/ deceased with increase of iron substitution. The magnetization and coercivity deceased, also the Curie temperature decreased from 360 K as x increased from 0.00 to 0.05. Magnetoresistence measurements were carried out, and the maximum MR ($\Delta$$\rho$/$\rho$(0)) was observed at 281 K, about 9.5 % in 10 kOe. The temperature of maximum resistance (R$\_$MAX/) decreased with increasing substitution of Fe ions and a semiconductor-metal transition temperature (T$\_$SC-M/) decreased too. This phenomena show that ferromagnetic transition temperature decreased by substituting Fe for Mn ions, it decreases double exchange interaction. This result accords with magnetic structure of neutron diffraction. Mossbauer spectra of La$\_$0.67/Ba$\_$0.33/Mn$\_$0.99/Fe$\_$0.01/ $O_3$were taken at various temperatures ranging from 15 to 350 K. With lowering temperature of the sample, two magnetic phases were increased and finally it showed the two sharp sextets of spectra at 15 K. The isomer shift at all temperature range is about 0.3 mm/s relative to Fe metal, which means that both Fe ions are Fe$\^$3+/ states.Fe$\^$3+/ states.

• Journal of Sensor Science and Technology
• /
• v.6 no.4
• /
• pp.328-336
• /
• 1997

The CdSe thin films were grown on the Si(100) wafers by a hot wall epitaxy method (HWE). The source and substrate temperature are $600^{\circ}C$ and $430^{\circ}C$ respectively. The crystalline structure of epilayers was investigated by double crystal X-ray diffraction(DCXD). Hall effect on the sample was measured by the van der Pauw method and studied on the carrier density and mobility dependence on temperature. From Hall data, the mobility was increased in the temperature range 30K to 150K by impurity scattering and decreased in the temperature range 150k to 293k by the lattice scattering. In order to explore the applicability as a photoconductive cell, we measured the sensitivity(${\gamma}$), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation(MAPD), spectral response and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in Cu vapor compare with in Cd, Se, air and vacuum vapour. Then we obtained the sensitivity of 0.99, the value of pc/dc of $1.39{\times}10^{7}$, the MAPD of 335mW, and the rise and decay time of 10ms and 9.5ms, respectively.