The Structural And Magnetic Properties Of The Mechanically Alloyed Ferro-antiferromagnetic Systems

Since the giant magnetoresistance (GMR) effect was first discovered in Fe/Cr multilayers, the intensive study on the Fe/Cr systems has possessed theoretical and practical significance. Though Fe and Cr are immiscible at room temperature, nanocrystalline solid solution can be prepared by mechanical alloying (MA). When Mn or V is doped into Fe-Cr alloys, the ternary alloys exhibit many interesting magnetic properties as a consequence of the variation in composition and temperature, however, the structural and magnetic properties of the ternary Fe-Cr-Mn(V) alloys prepared by mechanical alloying have not been reported yet. Consequently, the structural and magnetic properties of the MA ternary Fe-Cr-Mn(V) alloys had been intensively investigated on this thesis. For the important role of ferromagnetic/ antiferromagnetic interactions on the practice of the GMR equipments,α-Fe was chosen as the ferromagnetic material and the materials whose Néel temperatures are above room temperature and elemental composition is free of Fe as the antiferromagnetic one, and the relationship between the microstructures indicated by M?ssbauer spectroscopy and the ferro-antiferromagnetic interactions had been investigated on the thesis.The history and present status about the structural and magnetic properties of MA Fe-Cr systems have been briefly reviewed and summarized on the thesis. The basic phenomena of exchange bias and the exchange bias in thin film were summarized, and the development of the exchange bias in high-energy ball milled ferro-antiferromagnetic powders was also briefly introduced. The main contents are as follows:The structural properties of mechanically alloyed Fe₆₀Cr₄₀ powders under two different atmosphere were investigated by X-ray diffraction (XRD) and M?ssbauer spectroscopy. The results show that the residual N₂ and O₂ in the mill vials have drastically effect on the structures of the final milling products. When the vials are full of Ar without vacuumize, the paramagnetic Fe-Cr+N+O structure almost represent 100% of the final product after powders milled for 85h. When the vials are full of Ar with previous vacuumize, the final milling product is disorder nanocrystalline Fe-Cr solid solution with ferromagnetism similar to the bulk alloys.The structural and magnetic properties of MA Fe_xCr_90-xV₁₀(x=18,35) were investigated by XRD, M?ssbauer spectroscopy and magnetic measurements. A simple...