| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 88 === In this experiment, two-step evaporation method and a heating process was used to prepare Mn and Fe metallic films in turn with a short evaporation time. The CoxAg100-xwas overcoated on it by ion beam sputtering method. In CoxAg100-x/FeMn bilayer system, magnetoresistance characteristics by changing the thickness of thin films and conditions of heat treatment, and the effect of atomic ratio of Co and Ag was studied. The MR﹪(Δρ┬andΔρ┴)was measured at room temperature under applied magnetic field (H) up to 16.67kOe.
The MR﹪of single layer FeMn was positive which increased with increase of heat treatment temperature and decrease of thickness of the thin film. The FeMn with thickness of 80A had maximum positive MR﹪of 1.97﹪when heating at 500℃ for 20 minutes. As for the CoxAg100-x thin film, the MR﹪changed from negative to positive with decreasing thickness; meanwhile, it was affected by the atomic ratio of Co and Ag. Co64Ag36 film with thickness of 80A had a maximum positive MR﹪of 2.31﹪；Co20Ag80 with thickness of 2000A had the maximum negative MR﹪of 1.76﹪.
For the CoxAg100-x(80A)/FeMn system, positive MR﹪was affected by atomic ratio of Co and Ag, the thickness changes of FeMn, heat treatment conditions and roughness of the interface. The maximum MR﹪of 2.43﹪was obtained for Co64Ag35(80A)/FeMn(80A, annealed at 500℃ for 20 minutes). For Co20Ag80(tA,t = 80、216、432、864、1728、2000A)/FeMn(320A, annealed at 500℃ for 20 minutes) and Co20Ag80(tA, t = 80、216、432、864、1728、2000A)/FeMn(320A, annealed at 500℃ for 20 minutes) systems, the effect of positive MR﹪gradually decreased with the increase of Co20Ag80 thickness, and the sign of MR﹪ even became negative; it was close to a saturated negative magnetoresistance value finally. Co20Ag80(2000A)/FeMn(320A, annealed at 500℃ for 20 minutes) had the maximum negative MR﹪of 1.97﹪.
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