| Summary: | 碩士 === 國立彰化師範大學 === 物理學系 === 93 === The objective of this study is to investigate the magnetoresistance of patterned spin-valve devices .The fabrication processes were combining a two-step electron beam lithography and ion beam milling. Four nonmagnetic current/voltage leads were patched on the elliptical devices in the second step of electron beam lithography. Then, the magnetoresistance measurements were carried out under the external magnetic field applied along the long axis of the elliptical devices.
Comparing the magnetoresistance (MR) measurements of the patterned devices and sheet film, we found that the MR ratio of patterned devices was less than that of sheet film, which was due to the redeposition during the ion beam etching process. Moreover, temperature dependent MR measurements were also carried out. It has been found that the exchange biasing field (Hex) and minor loop shifting (Hin) decreased with increasing temperature, which is due to the strength of exchange biasing coupling and interlayer coupling decrease with increasing temperature. Furthermore, low field ac sensing current superimposed with various dc currents was introduced to study the possible spin transfer torque effect .It has been observed that Hex and Hin decreased with increasing dc current, which is believed to be caused by the joule heating effect. Besides, abrupt drops were observed in the minor loop and that occurred easily in small aspect ratio devices .The mechanism of the occurrence of abrupt drops is still unknown.
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