H. Niedoba

360° and 0° walls in multilayer Permalloy films

Abstract 360° walls have been investigated in Permalloy double films and multilayers with intermediate layers of carbon, prepared by electron beam evaporation and dc triode sputtering. They are nucleated in an easy axis field when a Bloch line in one layer is trapped at an inclusion. To minimise the magnetostatic energy through the layers, the 360° walls are inclined at an angle β

Field induced agglomeration in thin films of aqueous based magnetic fluids

Abstract We have made an initial study of field-induced agglomeration in thin layers of water-based magnetic fluids. The results are especially interesting for the case of a vertical applied magnetic field when the geometry of agglomeration assumes a pattern of uniform cylinders of equal height and diameter. This allows an upper bound to the packing fraction of elementary particles within chains to be established at ∼ 0.11. It is also believed that this disposition of agglomeration would enable the light transmission properties of the fluid to be readily correlated with the presence of chains.

First direct magneto-optical observations of quasi-Néel walls in double permalloy films

Abstract The first observations of quasi-walls have been performed in the double Permalloy layers separated by a thin carbon layer. This structure was brought to light due to the high-resolution Kerr effect with digital contrast enhancement. The experimental results are in good agreement with the theoretical predictions.

Magnetic properties and domain structure studies in dc triode‐sputtered permalloy/carbon multilayer films

Double‐layer and multiple‐layer thin films of permalloy with carbon as a intermediate nonmagnetic spacer were prepared by low‐energy dc triode sputtering. Coupling between the two layers of the double films is investigated on a series of samples with a fixed thickness of permalloy layers (dp = 300 A) and thickness of the carbon layer dc, varying from 0 to 25 A. Thickness dc = 10 A is found to be the limiting value for the carbon layer to be continuous and 20 A for domain structures in the two magnetic films to decouple. Saturation magnetization Ms, uniaxial anisotropy field, Hk, and coercive force Hc of multilayers with dc = 10 A and dp from 50 to 600 A (number of magnetic layers from 12 down to 1) are measured and found consistent with earlier results by other authors. Multiple domain walls in the multilayers are investigated by Lorentz electron microscopy.

Wall transitions in Permalloy double films

The transition from twin walls to superimposed walls and vice-versa, in two-layer laminated Permalloy films has been observed. Pictures of walls and quasiwalls have been taken using the high-resolution Kerr effect. The transition occurs at reproducible values of magnetic field applied in the hard direction of the sample, and experimental results indicate that it takes place due to the motion of Bloch lines along the walls. >

Domain wall pinning in amorphous CoZrNb films

A series of CoZrNb amorphous films, with thickness t ranging from 200 to 630 nm, has been studied by using several techniques: Kerr imaging, dc and audio frequency hysteresis loops, field dependence of the permeability, torque balance, broadband frequency susceptometer (1 kHz≤f≤500 MHz). Only samples with t≤500 nm have simple domain structures typical of an in‐plane anisotropy (with a small dispersion of the easy axis). Although domain walls (DW) are visible, they do not contribute to the initial permeability in the observed frequency range (even in the favorable case where the magnetic field is parallel to the easy axis), but they do play a role on the irreversible magnetization processes as shown by the existence of a critical field Hcr, typical of the onset of irreversible DW motion. These observations are consistant with a model which assumes that the DW are pinned at the film surfaces: the calculations give a negligible DW bulging contribution to the initial permeability, and predict the occurence of...

Magnetic and theoretical studies of NiFe layers coupled through a chromium interlayer

Abstract MBE prepared epitaxial Permalloy/Cr/Permalloy trilayers have been investigated by FMR and BH hysteresigraph. The film growth was monitored by Reflection High Energy Electron Diffraction (RHEED) and Auger Electron Spectroscopy (AES) which indicate Frank-Van der Merve growth of the Cr. The dependence of resonant field position and coercivity on the thickness of the Cr interfilm indicates the existence of an oscillatory long range exchange coupling of the Permalloy films. A transfer matrix theory previously used to analyse ferromagnetic coupling between magnetic films has been extended to include antiferromagnetic coupling and is used to interpret the FMR results.

Magnetic properties of double Permalloy films

Abstract Two-layered Permalloy films with a carhon intermediate layer of different thickness were investigated to correlate the coercivity values and magnetization process with the strength of the exchange coupling. The interpretation of strong, medium and weak coupling is proposed.

Properties of amorphous CoZr(RE) (RE=Gd, Sm, Dy) films with various uniaxial anisotropies, prepared by a new process

If a DC magnetic field is applied parallel to the plane of amorphous CoZr(RE) thin films during sputter depositing, a uniaxial anisotropy is formed the direction of which depends upon the choice of RE substituted and its concentration. When RE=Gd a perpendicular anisotropy Kp forms over a large concentration range, a spin reorientation process being at the origin of the process. A well-defined Kp is developed also in CoFeZrGd and CoZrGdSm films. CoZrGdDy films exhibit simultaneously a perpendicular and an in-plane uniaxial anisotropy. The related magnetization process and domain structures are quite peculiar.

Micromagnetics of two-layer laminated films with superimposed domains

The micromagnetic structure of the walls in two‐layer laminated films has been investigated using the high‐resolution longitudinal Kerr effect. Superimposed Bloch lines of opposite type (cross or circular) in the two magnetic layers are observed and interpreted. The mixed type of walls with twin and superimposed Neel segments is discussed. The magnetization distribution at crossing points between the twin walls nucleated in a hard axis field is deduced from the Kerr effect contrast of the walls and quasiwalls. The appearance of superimposed 360° walls and segments in 90° walls in samples with biaxial anisotropy is shown.