A Kerr microscope is presented, which on the one hand allows us to make, in a conventional manner, images of domains in thin films with perpendicular magnetic anisotropy. On the other hand, it is possible to heat the sample locally by a focussed laser beam and make images simultaneously. Therefore, it is possible to write domains thermomagnetically and further to observe temperature dependent magnetic reorientations. For demonstration domains have been created thermomagnetically in TbFe multilayers. Writing with low magnetic field leads to domains with a subdomain structure, as it has been found previously by Lorentz microscopy.
Oxidation process of Fe films under atmospheric conditions is depth limited such that an oxide covering layer with a well-defined thickness is formed by which the underlying metal is prevented from further oxidation. Iron thin film with an initial thickness d_{i}=4 nm was deposited onto 1.6 nm - V(110) buffer layer using UHV magnetron sputtering. The planar growth of Fe oxides was revealed by atomic force microscopy. X-ray photoelectron spectroscopy studies performed after 250 days of oxidation revealed formation of a hematite (α-Fe₂O₃) ultrathin film on the metallic rest of iron. Furthermore, low temperature magnetic measurements of the oxidised Fe ultrathin film revealed an exchange anisotropy which is imposed to the metallic rest. As a result, we have observed at low temperatures a shift and broadening of the hysteresis loops due to the exchange interaction at the metal-oxide interface.
A two-dimensional phenomenological model of patch-domain formation on unsaturation in strongly coupled tri- and multilayer antiferromagnets is presented. Domain patterns are simulated using a fast Monte Carlo algorithm. As a first example the autocorrelation function of the simulated domain pattern is compared with that of a measured Kerr image.
The surface sensitive magneto-optical Kerr effect methods and conversion as well as integral low-energy electron Mössbauer spectroscopy are used to compare the surface magnetic and microstructural properties of two Metglas alloys with compositions Fe_{80}Si_6B_{14} and Fe_{80}Si_{10}B_{10}. It is shown that the samples differ markedly both in the Mössbauer spectra and the surface hysteresis loops. While the ribbon with lower amount of Si is amorphous and characterized by three contributions corresponding to clusters with prevailing content of Fe and Si atoms, to clusters of mainly Fe and B atoms, and regions in between, the surface of the second sample is partially crystallized into bcc-FeSi crystals embedded in the residual amorphous matrix.
The influence of He^+ ion bombardment on magnetoresistance, magnetization reversal and domain structure of sputtered (Ni_{80}Fe_{20}(2 nm)/Au(2 nm)/Co(0.6 nm)/Au(2 nm))_{10} multilayers was investigated. The samples were bombarded using He^+(30 keV) ions with fluences D varied from 10^{13} to 3×10^{16} He^+/cm^{2}. With increasing D the following changes in magnetic properties were observed: (i) exponential decay of the saturation field of Co layers, (ii) progressive decrease in magnetoresistance as a result of degradation of Co layers perpendicular anisotropy, (iii) linear decrease in stripe domain period with log(D).
We use a microscopic theory taking into account the nearest-neighbour exchange and dipolar interactions to study two-dimensional magnetic nanodots and nanorings. Magnetic configuration is assumed to form an in-plane vortex (circular magnetization). We examine the dependence of the frequencies and profiles of spin waves on the dipolar-to-exchange interaction ratio d and the size of the dot (ring). Special attention is paid to some particular modes, including the lowest mode in the spectrum and the fundamental mode, the frequency of which proves almost independent of d. In the case of the lowest mode different profiles are observed: azimuthal, fundamental (quasiuniform) or highly localized, depending on d and the size. We also study the fundamental mode evolution including its hybridization and explain the selection rules.
In the article the results of the research aimed at the recognition of the correlation between the Ni-Fe film thickness and its magnetic domain structures are described. Magnetic thin films were prepared by pulse magnetron sputtering. Obtained thin film thicknesses were in the range of 47.6-326.0 nm. Magnetic domain structures were imaged using magnetic force microscopy. In order to obtain quantitative description of magnetic domains images, the algorithms designed for topography parameters determination were applied, enabling the comparison of specific factors related to the magnetic properties of the samples. Utilized approach provided the analysis of the impact of sputtering parameters on the morphological and magnetic properties of obtained films.
The commercial Fe-Si powder, produced by Högänes Corporation, represents promising soft magnetic material for technological applications. The powder consists of spherical particles with diameter up to 150 μm. Internal microstructure of the powder is formed by grains of diameter of about 30 μm. Each separate grain has a random orientation of the easy magnetization axis and is sufficiently large to split into several magnetic domains. A comparative study of the atomic force microscopy (AFM) topography and the corresponding magnetic force microscopy (MFM) images was employed in order to examine the correlation between the grain size, boundaries of grains and characterization of the magnetic domains, which gives us an important knowledge about possible behavior of particles under the influence of the external magnetic field and further utilization of the spherical Fe-Si particles in electrotechnical industry. The grain size and the crystallographic orientation of grains were analyzed by the electron backscattering diffraction (EBSD) technique.
The aim of this work is to study spin-wave excitations in the row of interacting two-dimensional nanodots in the vortex state. We use a discrete dipole model taking into account the nearest-neighbour exchange and dipolar interactions. Magnetic configuration of each dot is assumed to form an in-plane vortex (circular magnetization). We examine the dependence of frequencies and profiles of spin-wave modes vs. the dipolar-to-exchange interaction ratio and the dot separation. Special attention is paid to some particular modes: lowest-frequency azimuthal modes and the fundamental mode, an analogue of the uniform excitation. Some conclusions regarding the influence of the size of dots the row consists of as well as the chirality of neighbouring vortices are provided too.
Spatial magnetization distribution of cobalt layer is studied by means of three-dimensional micromagnetic simulations in the range of cobalt thickness d from 21 to 249 nm. In this range, a spin-reorientation phase transition occurs, while the cobalt thickness increases, from a state with in-plane magnetization, to a state with out-of-plane components of magnetization. An infinite cobalt layer is modelled by the 750 nm × 750 nm × d structure consisting of cubic cells of size of 3 nm and the periodic boundary conditions. For larger thicknesses, a labyrinth, partially closed, stripe structure has been found.
Interactions of domain walls are analyzed with relevance to formation of stationary bubbles (bound state of two domain walls) and bound states of many domains in one-dimensional systems. We investigate the domain structures in ferromagnets which are described with the Landau-Lifshitz equation as well as the domains in critical systems described with the Ginzburg-Landau equation. Supplementing previous author studies on the creation of hard bubbles [formed by one Bloch domain wall and one Néel (Ising) domain wall] in the presence of an external (magnetic) field, the soft bubbles consisting of two Bloch domain walls or two Néel (Ising) domain walls are studied in detail. The interactions of two domain walls of the same kind are studied in the framework of a perturbation calculus.
The growth of nanostructured materials by means of different deposition methods employing nanoporous anodic aluminum oxide membranes as patterned templates has been widely used during last years due to the outstanding features displayed by these nanoporous templates. Here we report on the synthesis, morphology and magnetic properties exhibited by novel magnetic 1D and 2D nanostructured materials having nanowire or antidot thin films geometry, respectively, together to that of geometrically diameter modulated ferromagnetic nanowires. Their magnetic properties will be analyzed and discussed based on the different anisotropic behavior derived from their morphological and microstructural features.
Interaction of domain walls in ferromagnetic stripes is studied with relevance to the formation of stable complexes of many domains. Two domain wall system is described with the Landau-Lifshitz-Gilbert equation including regimes of narrow and wide stripes which correspond the presence of transverse and vortex domain walls. The domain walls of both kinds are characterized with their chiralities (the direction of the magnetization rotation in the stripe plane) and polarities (the magnetization orientation in the center of a vortex and/or halfvortices), hence, their interactions are analyzed with dependence on these properties. In particular, pairs of the domain walls of opposite or like chiralities and polarities are investigated as well as pairs of opposite (like) chiralities and of like (opposite) polarities. Conditions of the creation of stationary bubbles built of two interacting domain walls are formulated with relevance to the situations of presence and absence of the external magnetic field.
The influence of current annealing on the complex domain structure in amorphous and nanocrystalline FeCoMoB microwire has been studied. The thickness of radial domain structure together with the switching field of single domain wall change as a consequence of variation of complex internal stress distribution inside metallic core. Firstly, radial domain structure thickness monotonously increases with increasing annealing DC current density for amorphous state. Switching field exhibits local minimum in nanocrystalline sample annealed at 500 MA/m^2 for 10 min when the lowest thickness of outer shell (182 nm) was observed. Such annealed sample (which magnetic properties exhibit excellent temperature stability) is suitable candidate for miniaturized sensor construction for sensing the magnetic field or mechanical stress.
The magnetometry and the magnetic force microscopy are used to study the influence of the magnetic domain size on the flux pinning in a superconducting/ferromagnetic bilayer (SFB), in which the S layer is niobium and the F layer is a Co/Pd multilayer with perpendicular magnetic anisotropy. The domain size is pre-defined using the angle-dependent demagnetization. The enhancement of pinning is found to be the strongest, up to a factor of 6, for narrow domains and small magnetic fields. This result differs from the behavior observed in the SFB in which the F layer is Co/Pt. The difference may be attributed to the degree of the disorder in the domain pattern.
The magnetic domain structure, its transformation with temperature, and the magnetization reversal in 20 nm La_{0.7}Sr_{0.3}MnO_{3} film grown on LaAlO_{3} substrate by off-axis magnetron sputtering at 700°C and post-annealed at 600°C were studied in a wide temperature range. The magnetic domains with either in-plane- or out-of-plane-orientation of the vector of spontaneous magnetization were observed in the same film depending on the prehistory. The domains with the in-plane magnetization were found to be more stable. Magnetization reversal of the film was shown to occur via the nucleation and motion of 180-degree head-to-head domain walls, the number and the type of which were found to be dependent on temperature. Moreover, the transition between two magnetization reversal regimes was found at 30 K.
Using the magnetoresistance measurements we study the phase transition line and the activation energy for vortex pinning in superconductor/ferromagnet bilayer, built of a ferromagnetic Co/Pd multilayer with perpendicular magnetic anisotropy, and a niobium film, with insulating layer in-between to eliminate proximity effect. The domain width is reversibly pre-defined using the angle-dependent demagnetization. We find that the enhancement of the activation energy for vortex pinning by magnetic domains is rather modest, by a factor of about 2.1. We attribute this to large domain width, and large dispersion of the domain width in this bilayer.
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