1,721,112 research outputs found
Diffracted-MOKE: What does it tell you?
No full textThe experimental and theoretical aspects of obtaining the magnetic information carried by laser beams diffracted from an array of nanosized magnetic objects are reviewed. Experimentally it will be shown that the magneto-optic Kerr effect (MOKE) hysteresis loops recorded for diffracted beams can be quite different from those recorded for the reflected beam. We will show that the diffracted MOKE (D-MOKE) loops are proportional to the magnetic form factor or, equivalently, to the Fourier component of the magnetization corresponding to the reciprocal lattice vector of the diffracted beam. In conjunction with micromagnetic simulations, the D-MOKE provides a powerful and non-destructive technique for investigating the magnetization reversal process in submicron-sized magnetic particles. The advantages and disadvantages of the D-MOKE technique will be compared to those of other techniques that yield related information (e.g. magnetic force microscopy, Lorentz electron microscopy and micromagnetic simulations)
Magnetization reversal via single and double vortex states in submicron Permalloy ellipses
No full textThe magnetization reversal mechanism in an array of submicron elliptical Permalloy elements with an aspect ratio 1.4:1 is investigated using the diffracted magneto-optic Kerr effect technique, Lorentz scanning transmission electron microscopy, and Lorentz transmission electron microscopy. The experimental results are interpreted from a comparison with micromagnetic simulations. The reversal mechanism is found to be dependent on the direction of the magnetic field and to occur via the formation of one or two vortices; the one vortex state is nucleated when the field is applied along the short axis. For the field applied along the long axis a mixture of one- and two-vortex states is observed at remanence
Magnetic Domain Structure and Magnetic Reversal in Elliptical Dot Arrays
No full textWe present a joint magnetic force microscopy analysis and Magneto-optical Kerr measurements of dot arrays that contain elliptical elements with different shape. In particular we have investigated the influence of the element shape on the domain structure in the remnant state. The single- or multiple domain nature of the magnetization at remanence is shown to depend strongly on how rounded or pointed each element is
Exchange-Induced Anisotropies at Ferromagnetic-Antiferromagnetic Interfaces above and below the Nèel Temperature
No full textThe determination of exchange bias and magnetic anisotropies in a Co layer in a single-crystalline FeF2 film was reported. A model was developed that quantitatively described the exchange bias and the anisotropies over the whole temperature range, both above and below Néel temperature TN. It was shown that large magnetic anisotropies were induced in a ferromagnetic film deposited on an antiferromagnetic substrate even well above TN of the antiferromagnet
Dynamic origin of first and second order phase transitions in magnetization reversal of elliptical nanodots
No full textWe study the magnetization reversal in elliptical nanodots with the external field applied exactly along the minor (hard) axis. By varying the magnitude of the applied field, several first and second order transitions take place and the system proceeds through magnetic configurations characterized by different symmetry properties. The dynamical matrix method is used to calculate the spin excitations as function of the applied field. This model system allows us to investigate the relationship between the singularities of the magnetization, the presence of soft spin excitations, and the symmetry properties of the static and dynamic magnetization fields. Rules that govern the transitions are formulated
Magnetization switching in Permalloy square ring magnets
No full textThe magnetization switching in Permalloy square rings was studied using diffraction magneto-optic Kerr effect combined with numerical micromagnetic simulations. A two-step switching process was shown as the external field was swept along both the ring edge and the diagonal. Results showed that in order to reproduce the observed two-step reversal, slight asymmetry has to be introduced into the ring shape
Magnetoresistance of single magnetic vortices
No full textThe magnetoresistance in a 1 micron Permalloy disk, that develops a vortex state during reversal, has been experimentally measured and modeled. The agreement between measurements and numerical simulations shows that the conventional anisotropic magnetoresistance effect is the main source of magnetoresistance. The results demonstrate that magnetoresistance can be used to determine the chirality of the vortex thereby improving the chances that patterned dot arrays could be used in data storage technology
Control of magnetic vortex chirality in square ring micromagnets
No full textWe investigate the effect of a deliberately introduced shape asymmetry on magnetization reversal in small, square-shaped, magnetic rings. The magnetization reversal process is investigated using the diffracted magneto-optical Kerr effect combined with micromagnetic simulations. Experimentally we find that the reversal path is sensitive to small (±1°) changes in the direction of the applied field. Micromagnetic simulations that reproduce the measured zeroth- and first-order loops allow us to identify the reversal mechanisms as due to different intermediate states, namely, the so-called vortex and horseshoe states. Based on our results we are now able to prescribe a methodology for writing a vortex state with specific chirality in these asymmetric rings. Such control will be necessary if patterned arrays of this kind are to be used as magnetic storage elements
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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