Magnetic studies of colossal magnetoresistance materials and FePt nanocrystals
Hyun, Changbae, 1974-
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This dissertation introduces scanning probe microscopy (SPM) and describes the construction and design of a home built low temperature magnetic force microscope (MFM). Then the magnetic coatings on atomic force microscope cantilevers with a focused ion beam (FIB) will be explained. This technique allows the convenient deposition of complex or expensive materials such as CoCrPt. With the MFM tip coated by FIB, the ferromagnetic domain structure of a La[subscript 0.67]Ca[subscript 0.33]MnO₃ film is studied as a function of an in-plane magnetic field below room temperature. Next I will discuss the use of chemically-synthesized FePt nanocrystals as a good candidate for high density storage media. This nanocrystal film showed sintering problems during the annealing process, which is essential to make FePt a hard ferromagnet. A silica overcoating method was used to prevent nanocrystal sintering, which allowed the MFM study of films made from these nanocrystals. I will also discuss resistance measurements of the FePt nanocrystals.