The Effect of Plastic Deformation on a Series of Thin Magnetic Films
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Thin magnetic films of FeSi and NiFe were grown on super-elastic Nitinol using dual ion beam and magnetron sputtering techniques, then submitted to varying degrees of lateral strain to induce plastic deformation in the thin magnetic film by (1) bending over a cylinder of fixed radius and (2) straining the sample laterally using an Instron 5566 materials tester. The magnetic properties were measured after each straining session via VSM using a sample holder developed for these experiments, which would allow the characterization. The quantity of plastic deformation introduced into the film was documented via optical microscopy. After films had been submitted to a maximal amount of strain, the overall adhesion of the film was tested using a Scotch tape approach. No effect of plastic deformation was observed by optical microscopy for the samples deformed by bending over a cylindrical object, and none of the thin films would detach from the Nitinol substrates when up to 4% strain was applied using this technique. The plastic deformation in the samples stretched by the Instron 5566 materials tester appeared to be inhomogeneous. Two types of plastic deformation were observed by optical microscopy on the samples stretched in the Instron. In the magnetron sputtered samples, cracks were introduced perpendicular to the strain direction at strains above 1 %, resulting in some of the thin film detaching from the Nitinol substrate. The DIBS FeSi-0.5% samples did not detach from the substrates upon straining up to 5%. After the larger strain cycles, small blisters over less than 1% of the film were observed by optical microscopy. The VSM measurements revealed at strains above 1% the magnetic properties of each sample changed permanently, indicating magneto-plastic effects. The magnetic measurements on the DIBS samples showed very little optical evidence of plastic deformation, which suggests that the plastic deformation is not homogeneous, and that the areas of the thin film exposed to large strains have very different magnetic properties from the original, unstrained film. Although several possible effects have been identified to explain the observed magneto-plastic properties, no conclusive theory has yet been developed to explain the observed magneto-plastic properties. Portions of the content related in this thesis was presented or published at the Fall meetings of the TSAPS [1, 2, 3], at the 2007 Texas State honor’s conference , at the 2008-MMM conference , and in IEEE Trans. on Magn. .