Electrical & Computer Engineering Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1658
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Item Analytical solution for the side-fringing fields of narrow beveled heads(American Institue of Physics, 1997-04-15) Mayergoyz, I. D.; Madabhushi, R.; Burke, E. R.; Gomez, R. D.By using conical coordinates, exact analytical solutions for three-dimensional side-fringing fields of recording heads that are beveled in the down-track direction are found. These solutions are derived under the assumption of zero gap length. The side-fringing fields for the two limiting cases of infinitesimally narrow heads and semi-infinitely wide heads are presented and compared.Item Spin-stand imaging of overwritten data and its comparison with magnetic force microscopy(American Institute of Physics, 2001-06-01) Mayergoyz, I. D.; Tse, C.; Krafft, C.; Gomez, R. D.A new technique of magnetic imaging on a spin-stand [Mayergoyz et al., J. Appl. Phys. 87, 6824 (2000)] is further developed and extensively tested. The results of successful imaging of digital patterns overwritten with misregistration ranging from 0.3 to 0.07 mm are reported. The results are compared with magnetic force microscopy (MFM) images and the conclusion is reached that the spin-stand imaging technique can provide (at least) the same level of resolution and accuracy as the MFM imaging technique.Item Switching characteristics of submicron cobalt islands(American Institute of Physics, 1996-07-01) Gomez, R. D.; Shih, M. C.; New, R. M. H.; Pease, R. F. W.; White, R. L.The magnetic characteristics of 0.230.430.02 mm3 cobalt islands were investigated using magnetic force microscopy in the presence of an applied field. The islands were noninteracting and showed a wide variety of single and multidomain configurations. The distribution of magnetization directions supports earlier models which suggest that crystalline anisotropy plays a dominant role in establishing a dispersion of easy axis directions about the long axis of the particles. The magnetic evolution, involving rotation and switching of individual islands, was observed at various points along the microscopic magnetization curve. A magnetization curve of an ensemble of islands was derived from the images and compares remarkably well with macroscopic M–H measurements.Item Domain wall motion in micron-sized Permalloy elements(American Institute of Physics, 1999-04-15) Gomez, R. D.; Luu, T. V.; Pak, O. A.; Mayergoyz, I. D.; Kirk, K. J.; Chapman, J. N.Item Domain configurations of Permalloy elements(American Institute of Physics, 1999-04-15) Gomez, R. D.; Luu, T. V.; Pak, A. O.; Kirk, K. J.; Chapman, J. N.Item Slow magnetization dynamics of small permalloy islands(American Institute of Physics, 2000-05-01) Koo, H.; Luu, T. V.; Gomez, R. D.; Metlushko, V. V.The conditions that lead to specific domain configurations and the associated switching characteristics of small permalloy islands were studied by using magnetic force microscopy. By measuring a large number of particles, it was established that islands that have nonzero remanent moments ~nonsolenoidal! exist in one of three distinct configurations, namely: ~a! true single domain, ~b! quasisingle domain with edge closure patterns, and ~c! multidomain with nonuniform internal magnetization. The configuration depended upon the island width as well as the aspect ratio. Islands that are 310 nm wide or less are true single domain particles at low aspect ratios (;1.87) and higher, while islands wider than 500 nm always exhibited edge closure domains even for very large aspect ratios. In the range between 310 and 500 nm, the onset of single domain behavior was a function of the aspect ratio and thickness. Our studies involving in situ applied field similarly revealed the mechanisms of the reversal processes for each of the configurations, which correlated quite well with the values of the switching fields.Item Dependence of the perpendicular anisotropy in Co/Au multilayers on the number of repetitions(American Institute of Physics, 2003-05-15) Gubbiotti, G.; Carlotti, G.; Albertini, F.; Casoli, F.; Bontempi, E.; Depero, L. E.; Mengucci, P.; Di Cristoforo, A.; Koo, H.; Gomez, R. D.The correlations between structure and magnetism in [Co(0.9 nm)/Au(5 nm)]XN multilayer films with different number of repetitions N510, 30, and 50, have been studied by the combined use of complementary structural and magnetic techniques, such as x-ray reflectivity, x-ray diffraction, and transmission electron microscopy, alternating gradient force magnetometry, magnetic force microscopy and Brillouin light scattering. On increasing the value of N, an overall improvement of the multilayer quality is observed which corresponds to a change in the micromagnetic structure and to an enhancement of the perpendicular anisotropy. These effects have been attributed to a reduction of the magnetostatic energy associated with the formation of perpendicular magnetic domains in multilayers with increasing number of layers repetitions.Item Quantification of magnetic force microscopy images using combined electrostatic and magnetostatic imaging(American Institute of Physics, 1998-06-01) Gomez, R. D.; Pak, A. O.; Anderson, A. J.; Burke, E. R.; Leyendecker, A. J.; Mayergoyz, I. D.A method for calibrating the force gradients and probe magnetic moment in phase-contrast magnetic force microscopy ~MFM! is introduced. It is based upon the combined electrostatic force microscopy EFM and MFM images of a conducting non magnetic metal strip. The behavior of the phase contrast in EFM is analyzed and modeled as a finite area capacitor. This model is used in conjunction with the imaging data to derive the proportionality constant between the phase and the force gradient. This calibration is further used to relate the measured MFM images with the field gradient from the same conducting strip to derive the effective magnetic moment of the probe. The knowledge of the phase-force gradient proportionality constant and the probe’s effective moment is essential to directly quantify field derivatives in MFM images.Item Low temperature behavior of magnetic domains observed using a magnetic force microscope(American Institute of Physics, 2001-06-01) Chung, S. H.; Shinde, S. R.; Ogale, S. B.; Venkatesan, T.; Greene, R. L.; Dreyer, M.; Gomez, R. D.A commercial atomic force microscope/magnetic force microscope ~MFM! was modified to cool magnetic samples down to around 100 K under a high vacuum while maintaining its routine imaging functionality. MFM images of a 120 nm thick La0.7Ca0.3MnO3 film on a LaAlO3 substrate at low temperature show the paramagnetic-to-ferromagnetic phase transition. Evolution of magnetic domains and magnetic ripples with decreasing temperature are also observed near the edge of a 20 nm thick patterned Co film on a Si substrate.Item Ultrahigh vacuum scanning tunneling microscopy/magnickel oxide filmsnetic force microscopy study of ultrathin iron films grown on polycrystalline nickel oxide films(American Institute of Physics, 2002-05-15) Dreyer, M.; Hwang, D. G.; Gomez, R. D.The thickness dependence of the topographic and magnetic structure of ultrathin Fe films grown on polycrystalline NiO films under ultrahigh vacuum ~UHV! conditions was studied to investigate the growth mechanism of the ferromagnetic film and the corresponding magnetic interaction with the antiferromagnetic substrate. Externally prepared NiO films of 60 nm thickness were cleaned by heating in UHV. Ultrathin layers of Fe in the range of 1–27 nm were deposited on top of the NiO film and were analyzed at specific coverages. Iron grows as a polycrystalline film with the grains increasing in size with the thickness. The contours of the underlying NiO crystallites were evident at low coverages but gradually disappeared as the Fe grains coalesced at thicker coverages. Magnetic force microscopy images of the 1 nm thick film show randomly oriented magnetic grains with an average domain size of 30 nm. With an increase in film thickness the size of the domains grows to about 200 nm at 15 nm of iron. At a film thickness of 19 nm cross-tie domain walls become visible, indicating the crossover of some parts of the film from random magnetic grains into continuous domains with in-plane magnetization. A further increase in the film thickness leads to larger in-plane domains, while there are some areas with localized grains on the surface.