Browsing by Author "Pokhil, Taras"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item A combined magnetooptic/magnetic force microscope study of Co/Pd multilayer films(Journal of Applied Physics (American Institute of Physics), 1997) Pokhil, Taras; Proksch, RogerWe have combined a magnetic force/atomic force microscope (MFM/AFM) with a magneto-optic (MO) microscope. This instrument combines the high spatial resolution of the MFM/AFM and its capability to correlate magnetic structure with the structure of the sample surface with the real-time imaging capabilities and large field of view of the MO microscope. Our MO/MFM setup is based on the Nanoscope III Multimode™ MFM/AFM (Digital Instruments, Santa Barbara, CA). Currently, the spatial resolution of the MO microscope is about 3 μm and polarization sensitivity is on the order of 0.5°. Using this instrument, we observed domain structures in Co/Pd multilayerfilms. We found that in a film with 20 Co/Pd layer pairs and 16 nm total thickness, nucleation of domains during sample remagnetizations occurs repeatedly in the same points, and that displacement of domain walls is unidirectional. The high topographic resolution of the AFM allowed us to show that domains nucleate at small defects on the sample surface. The depth of the defects is 1–2 nm, they are 20–30 nm wide and up to 500 nm long. The unidirectional displacement of the domain walls was found to correlate with the anisotropic structure of the sample surface.Item Domain wall displacements in amorphous films and multilayers studied with magnetic force microscope(Journal of Applied Physics (American Institute of Physics), 1997) Pokhil, TarasThe magnetic force microscope(MFM) was used to study the displacement of domain walls (DW) in amorphous TbFe alloy films and Co/Pd multilayerfilms with high spatial resolution. The reversible bending of domain wall segments pinned to defects and irreversible, jumplike displacement of domain wall segments were imaged with the MFM in an applied magnetic field. The maximum reversible displacement of domain walls was 50–100 nm and the length of the segments which reversibly curved in the field was about 150 nm. Measurement of the change in radius of curvature of a DW segment in response to an applied field allowed estimation of the DW energy density and self-demagnetizing field of the film acting on the DW. The DW energy density for the TbFe films was about 1 erg/cm2. It was shown that the self-demagnetizing field acting on a domain wall depends on the domain structure surrounding the studied DW segment. For instance, for a film with saturation magnetization 100 G and thickness 80 nm, which exhibited a mazelike domain structure, the demagnetizing field varied from 100 G in the center of a mazelike domain to 400 G near the edge of a domain. The irreversible displacement of a DW was not a continuous process. The 200–400 nm long DW segments exhibited jumplike motion over distances of 100–150 nm.Item IRM Quarterly, Volume 04, Number 4 (Winter 1994-1995). Cover article: Plethora of Postdocs is Plainly a Plus(University of Minnesota. Institute for Rock Magnetism, 1995) Oches, Eric; Housen, Bernard; Pokhil, TarasItem IRM Quarterly, Volume 07, Number 2 (Summer 1997). Cover article: Postdoctoral Transitions II(University of Minnesota. Institute for Rock Magnetism, 1997) Pokhil, TarasItem Magnetic domains and domain walls in pseudo-single-domain magnetite studied with magnetic force microscopy(Journal of Geophysical Research (American Geophysical Union), 1997) Pokhil, Taras; Moskowitz, BruceMagnetic domain and domain wall structures in pseudo-single-domain grains (5–20 μm) of magnetite (Fe3O4) were studied using magnetic force microscopy. Many of the observed micromagnetic features can be explained by the magnetostatic effects of surfaces and grain edges and interactions within and between walls. Domain walls were frequently subdivided into 1–3 opposite polarity segments separated by Bloch lines, although some walls contained no Bloch lines. Subdivided walls display a characteristic zigzag structure along the easy axis direction, where zigzag angles can be as high as 20°–40°. The zigzagging structure, in addition to wall segmentation, further minimizes the magnetostatic energy of the walls. Bloch lines can be (de)nucleated during wall displacement or after repeated alternating field (AF) demagnetization. Within individual walls, the number of Bloch lines and their pinning locations were found to vary after repeated AF demagnetization demonstrating that walls, like individual grains, can exist in several different local energy minima. The number of Bloch lines appears to be independent of domain state, but frequently the polarity of the wall was coupled with the direction of magnetization in the adjoining domains, such that wall polarity alternates in sign between adjacent walls across an entire grain. Even after the domain magnetization is reversed, the same sense of wall chirality is maintained across the grain producing unique grain chiralities. For one particular grain it was possible to reconfigure a likely three-dimensional (3-D) domain structure. The body and surface structures result primarily from a combined volume magnetostatic interaction between all grain surfaces and magnetocrystalline anisotropy. Finally, commonly observed open-flux features within the interior of grains or along grain edges terminating planar domains are inconsistent with the prediction of edge closure domain formation based on recent 2-D micromagnetic models. Our observations suggest that 3-D micromagnetic models are required to model results even for grains larger than 1 μm.Item Magnetic force microscope study of domain wall structures in magnetite(Journal of Applied Physics (American Institute of Physics), 1996) Pokhil, Taras; Moskowitz, BruceDomain walls (DW) in a small multidomain grain (≊20 μm) of magnetite (Fe3O4) exhibiting a planar domain pattern were studied using a magnetic force microscope(MFM). Most walls were subdivided with one or two Bloch lines and all walls displayed asymmetric MFM responses. Domain walls were observed to have small offsets either at the location of Bloch lines or at other locations without Bloch lines. The experimental data were described by a model in which (1) the easy axis of magnetization is not exactly parallel to the grain surface but is slightly inclined, and (2) there is also some plane dividing the grain in two parts with slightly different inclined easy axis directions. The inclined easy axis produces asymmetric spin distributions across the DW and wall offsets occur to reduce the surface magnetostatic energy of the wall.