Micromagnetic structures of magnetite and iron single crystals

The micromagnetic structures of magnetite and iron single crystals have been investigated using a magnetic force microscope (MFM) operated in an external magnetic field. Several MFM probe tips with various magnetic and geometric properties were utilized for this work. In many instances, comparison of MFM measurements of a sample structure made with the same tip magnetized in different directions provided additional useful information. Knowledge of the field dependence of the MFM tip magnetization was critical for accurate interpretation of the experimental data.; A millimeter thick magnetite single crystal with a (110) orientation allowed for the study of 180{dollar}spcirc,{dollar} 109{dollar}spcirc{dollar} and 71{dollar}spcirc{dollar} domain walls, the three fundamental types in bulk magnetite. The symmetry of MFM profiles across domain walls were consistent with the existence of Neel caps for all three wall types. Measurements of the perturbation of the domain walls' structure by the localized magnetic field of the MFM tip were analyzed. The influence of the tip field on a domain wall resulted in an overall more attractive interaction. The difference between opposite polarity domain wall profiles provided a qualitative measurement of the reversible changes in domain wall structure due to the tip field. The dependence of the measured alteration on tip-sample separation was fit with a power law at different positions across the domain wall. The rate of decay of the alteration was much slower than expected from a simple model.; The micromagnetics of the magnetization reversal process in epitaxial iron films of thickness 140 to 315 nm grown on (111) single crystal silicon surfaces have also been studied. The (111) orientation of these films resulted in a domain structure consisting of alternating surface polarity stripes of width approximately equal to the film thickness. Variations of the domain period and pattern complexity with applied field were correlated with the bulk magnetization curve measured using conventional magnetometry. A model of the remanent magnetization state and the reversal process was presented which qualitatively explained the experimental data. Preliminary results from a similar experiment on a nickel (001) epitaxial film, an analogous system, were consistent with the results for the iron.