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Magnetic properties of highly magnetostrictive amorphous glass-coated microwires are strongly correlated to the presence of a glass coating that introduces a spatially inhomogeneous stress field distribution. We investigate the influence of mechanical stresses on the inclination of magnetic domain walls in magnetic microwires. Magneto-optical Kerr effect imaging is used to compare the tilted orientation of the domain wall shape in as-cast and annealed microwires. Angular dependencies of magnetization loops measured by alternating gradient field magnetometry reveal that the change of domain wall tilting with annealing is related to the decrease of magnetic anisotropy with axial orientation. Finally, micromagnetic simulations are used to show that sufficiently high uniaxial magnetic anisotropy gives rise to the presence of observed charged domain walls with tilted orientation.

We present a study of the magnetic domains structure and the magnetization reversal in systems of stripes and dots patterned on Fe films by the atomic saw method. Continuous epitaxial 50 and 20 A Fe films have been grown by molecular beam epitaxy deposition method, then by applying strain on MgO monocrystalline substrate and controlling the dislocation slipping, micronic iron stripes and dots have been obtained. For the system of 1.4 μm wide stripes characterized by a strong uniaxial magnetic anisotropy (Ha=1500 Oe) resulting from a uniaxial relaxation of Fe lattice parameter, large magnetic domains have been observed by Kerr microscopy imaging. This structure is not directly correlated to the geometry of ribbons. It reveals the strong influence of the mutual dipolar coupling leading to a quasi-collective magnetization reversal. In contrast, Kerr microscopy observations done on samples structured into 1–3 μm dots show that the domain wall propagation is hindered by the net of orthogonal steps generated by...

The effect of a spin-polarized current crossing a domain wall in a thin and narrow Permalloy™ strip is studied by micromagnetic simulations, supported by a one-dimensional model of wall dynamics. We use the simplest way to incorporate the spin-polarized current effect in the micromagnetic formalism; namely, a local momentum transfer under the assumption that the current polarization is in local equilibrium. We predict current influence on wall velocity and mobility under field. However, in order to reach agreement with recent experiments, more than ten times larger currents would be required within this simplest model. Thus, more elaborate models of spin transfer are needed.

A method combining the nudged elastic band method with finite element micromagnetics is used to calculate minimum energy paths, global minima, metastable states and, most importantly, saddle points between energy minima. We study configurational anisotropy effects in thin permalloy elements, e.g., 5 nm thick squares. For squares with the size of 15–200 nm the ground states are so-called “leaf” states with the average magnetization along one of the diagonals. However a second state (“buckle”) becomes stable with the average magnetization along one edge at sizes larger than ∼80 nm. The superposition of the four easy axes leads to a combination of four and eightfold anisotropy. At ∼200 nm size both states have about the same energy so that the overall picture becomes that of an effective eightfold anisotropy.

A numerical framework is presented for the solution of the Landau–Lifshitz–Gilbert equation of magnetization motion using a semi-implicit Crank–Nicholson integration scheme. Along with the details of both space and time domain discretizations, we report on the development of a physically based self-consistency criterion that allows for a quantitative measurement of error in dynamic micromagnetic simulations. In essence, this criterion relies in recalculating from actual magnetization motion the imposed phenomenological damping constant. Test calculations were performed with special attention paid to the determination of suitable integration time steps.

Based on specific examples, we examine the consequence of spin-polarized current injection into confined model micromagnetic configurations, namely a high remanence state known as the S state and a low, though nonzero, remanence state called the Leaf state. Magnetization dynamics is solved in the space and time domain owing to the Landau–Lifshitz–Gilbert equation. It is shown that, within model bounds, the S state is not propitious to fast switching under the sole influence of a polarized current, even if disregarding the current induced field, whereas Leaf state switching characteristics become extremely complex as soon as due account is made for the latter.

The magnetization process in microfabricated NiFe wires was observed using a Kerr microscope. Magnetic wires were made from a 20-nm-thick NiFe film by using lift-off techniques. Their width Wand length L were designed as W= 0.5, 1.0 and 2.0 /Lm and L= 50/Lm, respectively. One end of the wire was connected to a square shaped head with a side of 2 W, which is designed to act as a domain wall source. In each wire, necks with different width of 0.2W, 0.6W, and 0.8W were introduced as artificial pinning sites of a domain wall. By using an oil-immersion lens (NA = 1.3) and a Hg lamp, magnetization reversals in very narrow wires, as narrow as 0.5 /Lm, were clearly observed. It is confirmed that domain wall penetration, pinning, depinning, and also the direction of wall motion are controllable using square shaped head and necks with optimized width.

The recent observation of a magnetization‐gradient‐related birefringence in ferromagnetic materials is reviewed. A new phenomenological description using an isotropic dielectric material law in which the dielectric tensor is a linear function of the components of the propagation vector of the light wave and of the symmetric part of the magnetization gradient tensor is proposed. The symmetry of this interaction is derived in terms of space and time inversion invariance requirements, adding information from perpendicular incidence experiments. The dielectric law contains only one material parameter and displays additional unexpected symmetries. It is compatible with all observations for the perpendicular incidence, in‐plane magnetization case. Its predictions for the case of oblique incidence and a gradient in the polar component of magnetization are found not to be in contradiction with experiments when precautions are taken to avoid asymmetric diffraction due to the polar Kerr effect.

It is proposed that the main source of contrast of vertical Bloch lines (VBLs) in bubble garnets, when viewed by means of anisotropic dark field optical imaging, is a microdeformation of the wall plane at line location. The motive force for wall tilting is the compensation of the monopolar σ charges borne by VBLs. The tilted wall section acts as a phase object and allows for the formation of line images with well‐defined symmetries and independent of the incident‐beam polarization. All these features agree fully with experimental evidence. An approximate model of the wall deformation is presented and shown to be consistent for a given thickness and material parameters with the results of an ab initio numerical computation of the 3D structure of a VBL. The implications of the microdeformation model in terms of line observability are analyzed and compared with experimental data.

Static and dynamic properties of (CoO/CoFeB)n multilayers have been investigated. An anisotropy field enhancement was evidenced when the CoO layer was deposited under the CoFeB layer. Tuning the relative CoFeB and CoO layers thicknesses, high ferromagnetic resonance frequencies up to 4 GHz were achieved. The coupling effect between the CoO and CoFeB layers was induced by a dipolar coupling due to the anisotropic roughness topology of the CoO layer. This anisotropic roughness was induced by the deposition geometry and evidenced by atomic force microscopy. The strength of the dipolar interfacial coupling was calculated thanks to Schlomann's model. Multilayer stacks were fabricated and the magnetic properties observed for the trilayers could be maintained.

Domains were imaged by magnetic force microscopy (MFM) on materials where the domain size exceeds the sample thickness by three orders of magnitude. Selected samples are a magnetooptical medium and ultrathin cobalt films, all with perpendicular magnetization. A strong domain contrast is observed in both cases. This fact is confronted to the usual theory of MFM image formation, in which the stray field from one body (tip or sample) is sensed by the other, without altering of the magnetization distributions. It is shown that the domain contrast in such extreme conditions cannot be explained with that theory. On the contrary, Abraham and McDonald’s model, which considers the response of the sample to the tip field, is quantitatively compared to experiment. It is shown to provide a good qualitative description of the results, but not a quantitative one, because of oversimplification.

We show in this article the first full three dimensional measurements of switching fields of a nanometer-scale magnetic particle. The field direction dependence of the switching fields can be successfully described by the uniform rotation model. Nevertheless, we could see that the Stoner–Wohlfarth form for the anisotropy function, which is often assumed together with the uniform rotation model, is an oversimplification. In order to reproduce the measured fields, one has to take into account higher order anisotropy terms. The complete form of the anisotropy function seems to be accessible only by magnetic measurements on each individual nanoparticle.

The magnetism of a Fe20Ni80/Cu/Co spin valve, in which a layer of FeNi containing a head-to-head transverse domain wall is coupled to a uniformly magnetized Co layer, via a nonmagnetic Cu layer, was investigated by micromagnetics (mainly numerical simulations). In equilibrium, due to the magnetostatic coupling between the layers, a quasiwall is created in the Co layer, which affects the domain wall profile in the FeNi layer. The dynamics of the domain wall under an applied field is also modified, and two opposite effects due to the spin valve geometry have been found, resulting, on the one hand, from the variation in the width of the domain wall and, on the other hand, from the additional damping of magnetization dynamics due to the cobalt layer.

Upon passing an a.c. electrical current along magnetic micro- or nanostrips, the measurement of a d.c. voltage that depends sensitively on current frequency and applied field has been recently reported by A. Yamaguchi and coworkers. It was attributed to the excitation of spin waves by the spin transfer torque, leading to a time-varying anisotropic magnetoresistance and, by mixing of a.c. current and resistance, to a d.c. voltage. We have performed a quantitative analysis by micromagnetics, including the spin transfer torque terms considered usually, of this situation. The signals found from the spin transfer torque effect are several orders of magnitude below the experimental values, even if a static inhomogeneity of magnetization (the so-called ripple) is taken into account. On the other hand, the presence of a small non-zero average Oersted field is shown to be consistent with the full set of experimental results, both qualitatively and quantitatively. We examine, quantitatively, several sources for this average field and point to the contacts to the sample as a likely origin., to be published in Journal of Applied Physics