1,721,073 research outputs found
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
Vortex rotation control in Permalloy disks with small circular voids
No full textWe studied the magnetization reversal of Permalloy disks with a small circular void either concentric or decentered. In both systems the reversal takes place via the nucleation and annihilation of a magnetic vortex. By applying the diffracted magneto-optic technique combined with numeric micromagnetic simulations we retrieved the information about the sense of rotation of the magnetization in the vortex state. For the disks with the concentric void no preferential rotation has been observed. For the case of decentered void, the sense of rotation of all probed disks is deterministically controlled by appropriately choosing the direction of the externally applied field and the void position with respect to the disk center
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
Domain wall displacement by current pulses injection in submicrometer Permalloy square ring structures
No full textThe magnetoresistance in submicrometer Permalloy square ring structures has been experimentally measured and modeled. The authors show that using an external field they can place a head-to-head domain wall at a selected corner of the ring and sense its position by magnetoresistance. They finally demonstrate that a domain wall can be reversibly and controllably displaced by current pulses of different polarity. Their observations can be explained by a directional spin-torque effect
Magnetoresistance of single Permalloy circular rings
No full textWe have measured magnetoresistance in single, 1 mm external diameter, Permalloy (Ni80Fe20) circular rings with varied inner holediameter of 150, 300, and 600nm and film thickness of 25 nm. The Permalloy ring structures and the 10-nm-thick, 250-nm-wide Aunanocontacts were fabricated on a SiO2/Si substrate using e-beam lithography. Using a four contact geometry we studied the dependenceof the magnetoresistance on the direction of the applied field. The experimental data are explained by considering only the conventionalanisotropic magnetoresistance effect. Numerical simulations of the current distribution within the samples combined with micromagneticsimulations of the field dependent magnetization profile, yield good agreement with the experimental data. Upon increasing the innerhole diameter (viz. decreasing the ring width) the magnetoresistance measurements show a transition of the reversal process from the‘‘vortex nucleation–displacement–annihilation’’ sequence to the ‘‘onion state–reversed onion state’’ sequence, typical of narrownanorings.r 2007 Elsevier B.V. All rights reserved
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
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
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
Metastable states during magnetization reversal in square permalloy rings
No full textThe magnetic reversal process in a two-dimensional array of permalloy square rings is presented. Rings of thickness of 25 nm, of lateral size of 2.1 μm, and with ring width of 240 nm were microfabricated using electron-beam lithography and lift-off techniques. Analysis of the diffracted magneto-optical Kerr effect hysteresis loops, magnetic force microscopy images, and micromagnetic simulations show that the magnetization reversal path depends on the direction of the in-plane applied magnetic field. On reducing the field from saturation, for fields along an edge or a diagonal of the square, the “onion” state is the stable state at remanence. In a narrow field range around reversal we find that the reversal occurs via a metastable intermediate state. For fields along the diagonal this intermediate state is a magnetic vortex. When the field is applied along an edge direction the intermediate state is a “horseshoe” state
Magneto-optic Kerr effect investigation of cobalt and permalloy nanoscale dot arrays: Shape effects on magnetization reversal
No full textUsing the magneto-optic Kerr effect (MOKE) and magnetic force microscopy we have investigated the shape dependence of magnetization reversal in a series of cobalt and permalloy nanoscale dot arrays. The patterns were produced by e-beam lithography combined with e-beam deposition and lift-off techniques. To avoid pattern to pattern variations in growth-induced anisotropy and or thickness, elliptical elements of varying aspect ratio were deposited simultaneously on a single substrate. All arrays were 1.0×2.5 μm tetragonal lattices and were fabricated with 300 Å thickness of cobalt and with 200 and 300 Å thickness of permalloy. From MOKE data we extract the field at which the onset of switching occurs for each array. For each material (viz. Co or permalloy), and thickness (200 or 300 Å), the switching field versus aspect ratio can be interpreted by a single nucleation field. The dependence of the nucleation barrier on the material and its thickness is discusse
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