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Fe-SiO_2 , and CoTiO_2 thin film magnetic and magneto- resistance effect

Author: JiaLiYun
Tutor: HouDengLu
School: Hebei Normal
Course: Condensed Matter Physics
Keywords: Discontinuous multilayer Magnetoresistance Diluted magnetic semiconductors Fe-SiO2
CLC: O484.43
Type: Master's thesis
Year: 2006
Downloads: 89
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Abstract


Magnetoresistance and diluted magnetic semiconductor have attracted more attention. For Magnetoresistance film, tunnel junction is instability and breakdown when there are low voltages. Moreover, granular films need great saturation field. For diluted magnetic semiconductors, CoTiO2 system is a hopeful diluted magnetic semiconductor because of its Tc higher than room temperature. In this paper, Fe-SiO2 discontinuous multilayers were fabricated onto glass substrates using dc facing-target magnetron sputtering and rf sputtering. CoTiO2 thin films were fabricated using a dc facing-target magnetron sputtering system. The microstructure, magnetic properties, and magnetoresistance were studied systemically with X-ray diffraction （XRD）, scanning probe microscope （SPM）, vibrating sample magnetometer （VSM）, and Physical Property Measurement System （PPMS）.Fe-SiO2 film annealed at 400°C showed smooth surface and apparent domain. The hysteresis loop has been obtained from VSM, and it showed that there was soft magnetic property at room temperature. The effect of Fe contents on the hysteresis loop of Fe-SiO2 film has been researched. Coercive force and remanence was increase with Fe content increasing. These films exhibit giant MR arising from spin-dependent tunneling and spin-dependent scattering between neighboring superparamagnetic Fe granules for both systems, and they show a maximum value of 14% at room temperature and thevalue of 30% at 240 K. The spin-dependent scattering and spin-dependent tuneling play important roles.The concentration of Co and annealing temperature （Ta） play an important role in CoTiO2 films. Co was in the +2 formal oxidation states throughout the film, and substitutes for Ti in the lattice create a nearby oxygen vacancy in the process. There was no evidence for either elemental Co or the cluster of metal Co in the films, and the magnetism in the films was caused by CoTiC>2 crystal.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > The nature of the films > Magnetic properties
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