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  • 1
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    Unconventional spin distributions in thick Ni80Fe20 nanodisks (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-05-10
    Description: We study the spin distributions in permalloy (Py: Ni 80 Fe 20 ) nanodisks as a function of diameter D (300 nm ≤  D  ≤ 1  μ m) and thickness L (30 nm ≤  L  ≤ 100 nm). We observed that beyond a certain thickness, for a fixed disk diameter, an unconventional spin topology precipitates which is marked by the presence of a divergence field within the magnetic vortex curl. The strength of this divergence changes anti-symmetrically from negative to positive—depending on the core polarity—along the axis of the cylindrical nanodisk. This is also accompanied by a skyrmion-like out-of-plane bending of the spin vectors farther away from the disk center. Additionally, the vortex core dilates significantly when compared to its typical size. This has been directly observed using magnetic force microscopy. We determined from the ferromagnetic resonance spectroscopy measurements that the unconventional topology in the thicker nanodisks gyrated at a frequency, which is significantly lower than what is predicted by a magnetic vortex based analytical model. Micromagnetic simulations involving dipolar and exchange interactions appear to satisfactorily reproduce the experimentally observed static and dynamic behaviors. Besides providing a physical example of an unconventional topology, these results can also aid the design of topologically protected memory elements.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Photo-enhanced magnetization in Fe-doped ZnO nanowires (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-07
    Description: An emerging branch of electronics, the optospintronics, would be highly boosted if the control of magnetic order by light is implemented in magnetic semiconductors' nanostructures being compatible with the actual technology. Here, we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to temperatures slightly below room temperature. This enhancement is related to the existence of an oxygen vacancy V O in the neighborhood of an antiferromagnetic superexchange Fe 3+ -Fe 3+ pair. Under illumination, the V O is ionized to V O + giving an electron to a close Fe 3+ ion from the antiferromagnetic pair. This light excited electron transition allows the transition of Fe 3+ to Fe 2+ forming stable ferromagnetic double exchange pairs, increasing the total magnetization. The results presented here indicate an efficient way to influence the magnetic properties of ZnO based nanostructures by light illumination at high temperatures.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-10-23
    Description: Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C–150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C–150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    On the polar decomposition of right linear operators in quaternionic Hilbert spaces (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-04-08
    Description: In this article, we prove the existence of the polar decomposition of densely defined closed right linear operators in quaternionic Hilbert spaces: If T is a densely defined closed right linear operator in a quaternionic Hilbert space H , then there exists a partial isometry U 0 such that T = U 0 T . In fact U 0 is unique if N ( U 0 ) = N ( T ). In particular, if H is separable and U is a partial isometry with T = U T , then we prove that U = U 0 if and only if either N ( T ) = {0} or R ( T ) ⊥ = {0}.
    Print ISSN: 0022-2488
    Electronic ISSN: 1089-7658
    Topics: Mathematics , Physics
    Published by American Institute of Physics (AIP)
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