77 research outputs found
Deconvoluting Reversal Modes in Exchange Biased Nanodots
Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been
deconvoluted into local, microscopic, bias separately experienced by nanodots
going through different reversal modes. The relative fraction of dots in each
mode can be modified by exchange bias. Single domain dots exhibit a simple loop
shift, while vortex state dots have asymmetric shifts in the vortex nucleation
and annihilation fields, manifesting local incomplete domain walls in these
nanodots as magnetic vortices with tilted cores.Comment: 17 pages, 3 figures. Phys. Rev. B in pres
Probing Magnetic Configurations in Co/Cu Multilayered Nanowires
Magnetic configurations in heterostructures are often difficult to probe when
the magnetic entities are buried inside. In this study we have captured
magnetic and magnetoresistance "fingerprints" of Co nanodiscs embedded in Co/Cu
multilayered nanowires using a first-order reversal curve method. In 200nm
diameter nanowires, the magnetic configurations can be tuned by adjusting the
Co nanodisc aspect ratio. Nanowires with the thinnest Co nanodiscs exhibit
single domain behavior, while those with thicker Co reverse via vortex states.
A superposition of giant and anisotropic magnetoresistance is observed, which
corresponds to the different magnetic configurations of the Co nanodiscs.Comment: 14 pages, 3 figure
Chirality control via double vortices in asymmetric Co dots
Reproducible control of the magnetic vortex state in nanomagnets is of
critical importance. We report on chirality control by manipulating the size
and/or thickness of asymmetric Co dots. Below a critical diameter and/or
thickness, chirality control is achieved by the nucleation of single vortex.
Interestingly, above these critical dimensions chirality control is realized by
the nucleation and subsequent coalescence of two vortices, resulting in a
single vortex with the opposite chirality as found in smaller dots.
Micromagnetic simulations and magnetic force microscopy highlight the role of
edge-bound halfvortices in facilitating the coalescence process.Comment: 15 pages, 4 figure
Controlling magnetization reversal in Co/Pt nanostructures with perpendicular anisotropy
We demonstrate a simple method to tailor the magnetization reversal
mechanisms of Co/Pt multilayers by depositing them onto large area nanoporous
anodized alumina (AAO) with various aspect ratios, A = pore depth/diameter.
Magnetization reversal of composite (Co/Pt)/AAO films with large A is governed
by strong domain-wall pinning which gradually transforms into a
rotation-dominated reversal for samples with smaller A, as investigated by a
first-order reversal curve method in conjunction with analysis of the angular
dependent switching fields. The change of the magnetization reversal mode is
attributed to topographical changes induced by the aspect ratio of the AAO
templates.Comment: 12 pages, 3 figure
Quantitative Decoding of Interactions in Tunable Nanomagnet Arrays Using First Order Reversal Curves
To develop a full understanding of interactions in nanomagnet arrays is a
persistent challenge, critically impacting their technological acceptance. This
paper reports the experimental, numerical and analytical investigation of
interactions in arrays of Co nanoellipses using the first-order reversal curve
(FORC) technique. A mean-field analysis has revealed the physical mechanisms
giving rise to all of the observed features: a shift of the non-interacting
FORC-ridge at the low-H end off the local coercivity H axis; a stretch
of the FORC-ridge at the high-H end without shifting it off the H axis;
and a formation of a tilted edge connected to the ridge at the low-H end.
Changing from flat to Gaussian coercivity distribution produces a negative
feature, bends the ridge, and broadens the edge. Finally, nearest neighbor
interactions segment the FORC-ridge. These results demonstrate that the FORC
approach provides a comprehensive framework to qualitatively and quantitatively
decode interactions in nanomagnet arrays.Comment: 19 pages, 4 figures. 9 page supplemental material including 3 figure
Homodyne-detected ferromagnetic resonance of in-plane magnetized nanocontacts: Composite spin-wave resonances and their excitation mechanism
This work provides a detailed investigation of the measured in-plane field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an extended Co/Cu/NiFe pseudo-spin-valve stack using a nanocontact (NC) geometry. The magnetodynamics are generated by a pulse-modulated microwave current, and the resulting rectified dc mixing voltage, which appears across the NC at resonance, is detected using a lock-in amplifier. Most notably, we find that the measured spectra of the NiFe layer are composite in nature and highly asymmetric, consistent with the broadband excitation of multiple modes. Additionally, the data must be fit with two Lorentzian functions in order to extract a reasonable value for the Gilbert damping of the NiFe. Aided by micromagnetic simulations, we conclude that (i) for in-plane fields the rf Oersted field in the vicinity of the NC plays the dominant role in generating the observed spectra, (ii) in addition to the FMR mode, exchange-dominated spin waves are also generated, and (iii) the NC diameter sets the mean wave vector of the exchange-dominated spin wave, in good agreement with the dispersion relation
Continuously graded anisotropy in single (Fe53Pt47)100−xCux films
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We report on continuously graded anisotropy. During deposition, a compositional gradient is achieved by varying the Cu concentration from Cu-rich (Fe53Pt47)70Cu30 to Cu-free Fe53Pt47. The anisotropy gradient is then realized after annealing using the composition dependence of the low-anisotropy (A1) to high-anisotropy (L10) ordering temperature. The critical role of the annealing temperature on the resultant anisotropy gradient is investigated. Magnetic measurements support the creation of an anisotropy gradient in properly annealed films which exhibit both a reduced coercivity and moderate thermal stability. These results demonstrate that an anisotropy gradient can be realized, and tailored, in single continuous films without the need for multilayers
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