Electrical & Computer Engineering Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1658
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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.Item Magnetoresistive effects in planar NiFe nanoconstrictions(American Institute of Physics, 2004-06-01) Florez, S. H.; Dreyer, M.; Schwab, K.; Sanchez, C.; Gomez, R.D.This study focuses on domain wall resistance in Ni80Fe20 nanowires containing narrow constrictions down to 15 nm in width. Distinct differences in the magnetoresistance curves were found to depend on the constriction size. Wider constrictions are dominated by the overall anisotropic magnetoresistance of the structure, while constrictions narrower than ;40 nm exhibit an additional distinct contribution from a domain wall. The effect is negative and typically varies from 1% to 5%.Item „(Towards) Spin-polarized scanning tunneling microscopy of NiFe films on a chromium„001… single crystal: Growth and electronic structure of Permalloy(American Institute of Physics, 2005-05-10) Dreyer, M.; Lee, J.; Krafft, C.; Gomez, R.This paper shows spin-polarized tunneling on the terraces of antiferromagnetic chromiums001d. Details on the morphological and chemical composition are shown as a function of various stages of surface preparation, and protocols for obtaining Crs001d that reveal spin-polarized contrast are reported. On the clean crystal the chromium surface state at the Fermi level could be observed. The spin splitting of the state was measured by using an iron coated tungsten tip. A spin polarization of 10% was observed. The properties of NiFe grown on Crs001d measured using nonpolarized tunneling spectroscopy are also reported. Monolayer thick permalloy grows in Volmer–Weber mode, exhibiting pyramidal islands oriented along the chromium k110l direction. Spectroscopic data reveal that NiFe alloying is preserved.