24 research outputs found
Materials optimization for magnetic MEMS
By highlighting magnetomechanical effects such as the DeltaE-effect, and developing modeling code that integrates magnetoelasticity with microelectromechanical systems, it is shown that a simple cantilever system can have a sensitivity to mass loading at the attogram level. The requirements on the magnetoelastic materials for such devices are described, and progress towards achieving optimized material is reviewed. The possibility for deployment of such systems in security, healthcare, and bioscience is outline
Detailed study of the hysteresis loops for annealed amorphous alloy wires having vanishing magnetostriction
The evolution of Barkhausen events during the magnetization process in current and furnace annealed Co-based amorphous wire having vanishing magnetostriction, /spl lambda//sub s/, is reported. Their origin is explained using the core-shell model commonly accepted for this class of wire. It is argued that the application of stresses during the annealing process, in wire having slightly negative and slightly positive /spl lambda//sub s/, changes the internal magnetic domain structure. Anisotropy induced by anelastic creep can be used to avoid the formation of these Barkhausen events. The behavior of the coercivity and susceptibility is also reported
Finite-element analysis on cantilever beams coated with magnetostrictive material
The main focus of this paper is to highlight some of the key criteria in successful utilization of magnetostrictive materials within a cantilever based microelectromechanical system (MEMS). The behavior of coated cantilever beams is complex and many authors have offered solutions using analytical techniques. In this study, the FEMLAB finite-element multiphysics package was used to incorporate the full magnetostrictive strain tensor and couple it with partial differential equations from structural mechanics to solve simple cantilever systems. A wide range of geometries and material properties were solved to study the effects on cantilever deflection and the system resonance frequencies. The latter were found by the use of an eigen-frequency solver. The models have been tailored for comparison with other such data within the field and results also go beyond previous work
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Transverse field-induced nucleation pad switching modes during domain wall injection
We have used magnetic transmission soft X-ray microscopy (M-TXM) to image in-field magnetization configurations of patterned Ni80F20 domain wall "nucleation pads" with attached planar nanowires. Comparison with micromagnetic simulations suggests that the evolution of magnetic domains in rectangular injection pads depends on the relative orientation of closure domains in the remanent state. The magnetization reversal pathway is altered by the inclusion of transverse magnetic fields. These different modes explain previous results of domain wall injection into nanowires
Direct imaging of domain-wall interactions in Ni80Fe20 planar nanowires
We have investigated magnetostatic interactions between domain walls in Ni80Fe20 planar nanowires using magnetic soft x-ray microscopy and micromagnetic simulations. In addition to significant monopole-like attraction and repulsion effects we observe that there is coupling of the magnetization configurations of the walls. This is explained in terms of an interaction energy that depends not only on the distance between the walls, but also upon their internal magnetization structure
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Imaging of magnetic DW injection processed in patterened Ni80Fe20 structures
Magnetization reversal in patterned ferromagnetic nanowires usually occurs via domain wall (DW) nucleation and propagation from one end (or both ends) of the wire which can be significantly reduced by a large, magnetically soft pad on one of the wire ends. These 'nucleation pads' reverse at lower fields than an isolated nanowire and introduce a DW to the wire from the wire end attached to the pad. Once a critical 'injection' field is reached, the DW sweeps through the wire, reversing its magnetization. Nucleation pads are frequently used as part of nanowire devices and experimental structures. Magnetic-field-driven shift register memory can include an injection pad to write data while those attached to nanowire spiral turn sensors act as both a source and sink of domain walls. Both of these devices use two-dimensional wire circuits and therefore require the use of orthogonal in-plane magnetic fields to drive domain walls through wires of different orientations. These bi-axial fields can significantly alter the fields at which DW injection occurs and control the number of different injection modes. We have used magnetic transmission soft X-ray microscopy (M-TXM) [6] providing 25nm spatial resolution to image the evolution of magnetization configurations in patterned 24nm thick Ni{sub 80}Fe{sub 20} rectangular nucleation pads and attached wires during DW injection. The structures consisted of 2 {micro}m x 3 {micro}m nucleation pads with wires of width 200 nm, 300 nm or 500 nm attached Comparing the magnetic configuration of the injection pads with micromagnetic models, we find that the relative orientation of closure domains in the remanent magnetization configuration of injection pads determines the reversal pathway that follows, although this is further affected by applied transverse fields. Micromagnetic simulations were performed using a hybrid finite element/boundary element code. The magnetic elements were designed with 20 nm thickness and discretized into a mesh of tetrahedral elements with a maximum cell size of 20 nm. Material properties for bulk permalloy were used, i.e. exchange stiffness A = 1.3 x 10{sup -11} J/m, saturation magnetization M{sub S} = 800 kA/m, magneto-crystalline anisotropy K = 0 Jm{sup -3}, damping constant a = 0.01. A linearly increasing magnetic field (1 Oe/ns) was applied parallel to the wire long axis to simulate switching fields. The dimensions of the simulated structures mimicked the essential features of the experimental structures, although edge roughness was neglected from the model. The remanent magnetization state of the pad with no transverse field consists of a uniform magnetization aligned with the wire axis, with closure domains at the edges facing and joining the wire. When H{sub y} = 0 Oe and H{sub x} = 20 Oe, the magnetization state of the pad buckles, forming eight domains, half of which have magnetizations rotated away from the x-axis. As H{sub x} is increased, the rotation of the domains become larger and the non-rotated domains shrink A transverse field applied in addition to the axial field exhibits a more complex modes of magnetization reversal in the pad (Fig. 1). We understand the pathway of pad magnetization more generally by using micromagnetic simulations. Two initial configurations are shown in Fig. 2 with the closure domain on the left-hand edge of the pad either parallel or anti-parallel to both closure domains on the righthand edges of the pad. As H{sub x} is increased to inject a domain wall, the pad magnetization states changed to vortex states, as observed by M-TXM. At higher fields, the magnetization of the modeled pad became single-domain, although closure domains remained at fields up to H{sub x} = 90 Oe. This supports the suggestion that experimentally observed multi-modal injection is due to the magnetization state of the pad. In summary, the relative orientation of closure domains in the pads determines the magnetization reversal pathway under an axial field. However, the addition of transverse fields can alter these and lead to the pads undergoing reversal under lower axial fields. Our observations have wider implications for experiments and devices using patterned magnetic wires
DOMAIN WALL PINNING IN INHOMOGENEOUSLY DEFORMED AMORPHOUS ALLOYS
Inhomogeneous deformation in amorphous alloys is characterized by local regions of intense shear. Experiments on VITROVAC 0040 (Fe40Ni40B20) supplied by Vacuumschmelze (Hanau, Germany) show a direct correlation between the number density of the shear bands and the coercive field after inhomogeneous deformation by cold rolling. The deformation process is also shown to induce an off axis magnetic anisotropy whose mean value is large compared to other residual and induced anisotropies in these materials. On this basis a domain structure is proposed for deformed material, and a model for coercivity based on domain wall pinning at residual stresses remaining after deformation is shown to lead to reasonable estimates of the coercive force