ORCID Profile
0000-0002-7426-7731
Current Organisation
University of Leeds
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Publisher: AIP Publishing
Date: 10-2010
DOI: 10.1063/1.3488618
Abstract: Broadband ferromagnetic resonance responses for metallic single-layer and bilayer magnetic films with total thicknesses smaller than the microwave magnetic skin depth have been studied. Two different types of microwave stripline transducers were used to excite and detect magnetization precession: a coplanar waveguide and a microstrip line both with characteristic width larger than the free propagation path for traveling spin waves along the film. Both transducers show efficient excitation of higher-order standing spin wave modes across the film thickness in s les 30–91 nm thick. The ratio of litudes of the first standing spin wave to the fundamental resonant mode is independent of frequency for single-layer permalloy films. In contrast, we find a strong variation in the litudes with frequency for cobalt–Permalloy bilayers and the ratio is strongly dependent on the ordering of layers with respect to a stripline transducer. Most importantly, cavity ferromagnetic resonance measurements on the same s les show considerably weaker litudes for the standing spin waves. All experimental data are consistent with expected effects of eddy currents in films with thicknesses below the microwave magnetic skin depth. Finally, conditions for observing eddy current effects in different types of experiments are critically examined.
Publisher: American Physical Society (APS)
Date: 06-12-2011
Publisher: American Physical Society (APS)
Date: 12-09-2011
Publisher: Springer Science and Business Media LLC
Date: 17-12-2006
DOI: 10.1038/NMAT1809
Abstract: Exchange bias is commonly manifested as the hysteresis-loop shift observed when a ferromagnet is in contact with an antiferromagnet. Here, we report observations of exchange bias with unusual features of a ferromagnet in contact with a spin glass, demonstrating that this is a phenomenon of greater generality. The easily measured properties of the ferromagnet allow access to the internal magnetic degrees of freedom of the glass to which they are coupled. Our results show that a Co/CuMn bilayer system exhibits all the rich phenomena of coercivity enhancement, bias-field shifts and training effects associated with a conventional ferromagnet/antiferromagnet system. Nevertheless, striking differences arise, such as an orientation reversal of the bias field in a small temperature range just below the blocking temperature. We argue that all features can be understood within the context of a random-field model for long-ranged oscillatory Ruderman-Kittel-Kasuya-Yosida (RKKY) coupled spins.
Publisher: American Physical Society (APS)
Date: 12-12-2022
Publisher: American Physical Society (APS)
Date: 17-01-2012
Publisher: EDP Sciences
Date: 09-2012
Publisher: AIP Publishing
Date: 30-04-2018
DOI: 10.1063/1.5027202
Abstract: Tapered coplanar waveguides with integrated photoconductors were designed, fabricated, and measured, with pulsed transmission results comparing well with High Frequency Structure Simulator simulations which predict increased confinement and electric field concentration in the tapered region. Devices made with titanium/gold metallisation were used to demonstrate transmission and confinement, while the magnetoresistive properties of devices with cobalt/copper multilayers were used to demonstrate the field concentration. In the latter case, a mathematical framework was developed to understand the relationship between tapering effects and the picosecond magnetoresistance response.
Publisher: American Physical Society (APS)
Date: 08-02-2011
Publisher: AIP Publishing
Date: 04-05-2005
DOI: 10.1063/1.1857432
Abstract: Fe 3 O 4 ∕ Ga As hybrid structures have been studied using reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), x-ray magnetic circular dichroism (XMCD), and low-temperature vibrating-s le magnetometry (VSM). The s les were prepared by oxidizing epitaxial Fe thin films in a partial pressure of 5×10−5mbar of oxygen at 500K for 180s. Clear RHEED patterns were observed, suggesting the epitaxial growth of Fe oxides with a cubic structure. The XPS spectra show that the oxides were Fe3O4 rather than γ-Fe2O3, as there were no shake-up satellites between the two Fe 2p peaks. This was further confirmed by the XMCD measurements, which show ferromagnetic coupling between the Fe cations, with no evidence of intermixing at the interface. The VSM measurements show that the films have a magnetic uniaxial anisotropy and a “quick” saturation property, with the easy axes along the [01¯1] direction. This detailed study offers further insight into the structure, interface, and magnetic properties of this hybrid Fe3O4∕GaAs(100) structure as a promising system for spintronic application.
Publisher: AIP Publishing
Date: 27-02-2017
DOI: 10.1063/1.4977490
Abstract: We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG s les with thickness varying from 14.8 nm to 80 nm, with the Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics.
Publisher: American Physical Society (APS)
Date: 03-12-2015
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Mannan Ali.