J.P. Jakubovics

Determination of domain wall structures in thin foils of soft magnetic alloy

Abstract Domain wall structures in thin foils of a Ni-Fe-Co-Ti alloy have been determined using the differential phase contrast mode of Lorentz electron microscopy. Among the advantages of this mode are that easily interpretable signals can be obtained whilst the experiment is in progress. In accord with theoretical expectation the walls were found to have a vortex structure whose width increased linearly with foil thickness.

A magnetic and high resolution structural investigation of Pt/Co multilayers

Abstract The paper discusses the results of experiments on sputter-deposited polycrystalline Pt/Co multilayer films. A particular aim was to measure the magnetic properties of multilayers with differing periods and layer thicknesses and to examine their atomic scale structure using high resolution electron microscopy. We show that the magnetic properties of the multilayers are strongly dependent of their microstructure. Perpendicular magnetisation at small cobalt layer thickness corresponding to one or two monolayers is associated with a strong surface anisotropy and a columnar and coherent crystal growth texture. At greater bilayer thicknesses this effective anisotropy and mode of growth is lost.

Coercivity and microstructure of melt‐spun Sm(Fe11Ti)

Amorphous Sm(Fe11Ti) ribbons were prepared by melt spinning. After heat treatment, very fine grains (≊50 nm) of the ThMn12‐structure phase were obtained with no signs of a separate intergranular phase. Each grain appears to be a single domain. The maximum room‐temperature coercivity is 0.56 T, rising to 1.20 T at 11 K. A model is proposed for the coercivity which is based on an analogy with the random anisotropy model of amorphous magnetism. It gives the correct magnitude of the coercivity, and suggests it should vary as the reciprocal of the crystallite size.

Direct observation of the interaction between magnetic domain walls and dislocations in iron

Abstract The influence of dislocations on magnetisation processes in iron has been investigated by high voltage Lorentz microscopy. The dominant interaction between magnetic domain walls and dislocations changes with increasing strain level. Thin foil coercivities vary from 0.5 to 3 Oe for strain levels 0.6 to 16.4% respectively.

TEM studies of domains and micromagnetic processes in structural steels

Abstract The magnetic domain structure of a series of steel specimens heat treated to produce microstructures ranging from martensitic/bainitic to ferritic/pearlitic has been studied by Lorentz microscopy. Furthermore micromagnetic processes have been observed using an in-situ magnetizing device. The results are used in the interpretation of the results of measurements by magnetic nondestructive techniques.

Wall structure in cobalt thin films

Abstract Micromagnetic simulation of the magnetisation distribution in stripe domains found in cobalt foils with an inclined c -axis leads to the conclusion that the walls possess a marked two dimensional nature. Such walls should give rise to strongly asymmetrical profiles when observed experimentally by Lorentz microscopy. Differential phase contrast electron micrographs confirm these findings, although discrepancies in detail still remain.

A TEM investigation of microstructure and domain configurations in melt-spun SmFe11Ti

Abstract Melt-spun ribbons of composition SmFe11Ti were annealed at temperatures in the range 650–825°C for 10–30 min. The maximum coercivity Hc = 0.56 T, was obtained by annealing at 800°C for 20 min. The microstructures were determined by TEM. Lorentz electron microscopy was used to image domain walls. The specimens consist of single-domain grains of the ThMn12 structure Sm(Fe11Ti) phase, plus, in some cases, α-Fe. The reductions in Hc in the under- and over-annealed specimens are attributed to irregularities in grain boundaries and growth of α-Fe grains, respectively.

Effect of magnetostriction on 90° domain walls in thin films

Abstract The structure of 90° domain walls in thin ferromagnetic films has been computed, with the inclusion of magnetostriction, in the form of an induced uniaxial anisotropy. It is found that the wall width decreases with increasing induced anisotropy. For a given anisotropy, the relative decrease is greater in thicker films. For the thicknesses of up to 200 nm studied here, the decrease of wall is small for realistic values of induced anisotropy, but for larger film thickness the effect of magnetostriction may be important, and will have to be taken into account.

Mechanism of bubble motion in implanted garnets

Abstract The motion of bubble domains in implanted garnets is controlled by charged walls. The “flip” phase of the motion of charged walls is investigated in detail. It is shown that the mechanism of “flip” is different according to whether the charged wall is loaded with a bubble or not.

Observations of magnetic domain structures in thick foils of Ni-Fe-Co-Ti alloy

Abstract The domain structure of thick foils of a 33.8Ni-51.0Fe-14.0Co-1.2Ti (wt%) alloy has been studied by high voltage transmission Lorentz microscopy. Complex domain structures and wall images have been observed. Periodic domain structures have been interpreted as sets of two-dimensional vortex walls.