[en] In reference to the work of Hashimoto and Marukawa the complex patterns which are produced by the electron diffraction contrast of overlapping stacking faults are investigated further, especially including absorption. (auth.)

[en] By means of a diaphragm in front of the detector, the SE-contrast of magnetic domains observed in a SEM has been improved and a resolution of 0.17 G . cm obtained. Investigations on SmCo₅ show that the contrast can be improved by increasing the acceleration voltage and tilting the specimen. (author)

[en] A Lorentz-electron microscopic investigation of Co₅Sm single crystals reveals that the influence of dislocations on the precipitation and on Bloch walls gives an important contribution to the coercive field in Co₅Sm. No pinning of domain walls occurs at basal dislocations. The observed strong pinning at prismatic dislocations is due to long-range interactions and is interpreted in terms of a micro-magnetic continuum theory. It is found that for prismatic a-edge dislocations the maximum interaction force on domain walls is about 54 dyn/cm. The deformation strains, which occur because of the coherent precipitation of Co₇Sm₂ and Co₁₇Sm₂, create an interaction force on domain walls of the order of magnitude 1 x 10^-5 dyn for a precipitate at the initial stage of precipitation. (author)

[en] TEM investigations of SmCo₅ single crystals grown from the melt revealed with respect to lattice defects a and c + a dislocations, and stacking faults lying predominantly on the basal plane and on the (1121)-pyramidal planes. This alloy is important as a hard-magnetic material. From the separation of the dislocations a low stacking fault energy is concluded. (author)

[en] The interaction between the microstructure and the magnetic domains determines the coercivity of REPM. The crystal lattice defects and precipitates, which act as domain wall pinning centres, are examined in single-phase Co⁵RE magnets and in precipitation hardened 17:2-magnets using electron microscopy. In single-phase 5:1-magnets the magnetization reversal occurs by nucleation and growth of reversed domains. Grain boundaries are found to act as strong pinning centres for domain walls. The coercivity mechanism of precipitiation hardened 17:2-REPM is controlled by domain wall pinning at a continuous copper containing precipitation phase and is interpreted in terms of a micromagnetic theory for domain wall pinning. (Author)

[en] A transmission electron microscopic investigation has been undertaken of the heterogeneous nucleation of precipitates present in Co₅Sm crystals. By means of computer simulation of the displacement fringe contrast, planar extrinsic faults lying in the basal plane and bordered by Frank partial dislocations were identified as Co₁₇Sm₂ precipitates which nucleate at prismatic c-edge dislocations. Further nucleation centres, which were also found, are a-edge dislocation dipoles in the basal plane, prismatic a-edge dislocations and c + a screw dislocations. These experimental results are in agreement with calculations according to continuum theory. (author)

[en] In Nd-Fe-B based permanent magnets a high magnetocrystalline anisotropy of the hardmagnetic phase is necessary for a high intrinsic coercivity. In fact, metallurgical parameters (distribution of phases, chemical composition and crystal structures of phases) and processing parameters (alloy preparation, size and shape of particles, sintering and annealing treatments) determine the value of the coercive force of each sintered Nd-Fe-B magnet. Our analytical electron microscope study shows that 'melt-spun' and sintered Nd-Fe-B based magnets contain more or less a distribution of nucleation centres for reversed domains, such as iron-rich phases and α-iron precipitates within the hardmagnetic 2:14:1-grains. A continuous non-magnetic layer phase between the hardmagnetic 2:14:1-grains increases the expansion field of reversed domains and increase the coercivity. In 'melt-spun' magnets the contribution of the pinning of magnetic domain walls becomes effective during the magnetization reversal process. (Author)

[en] In order to investigate the flux pinning process in a suitable model system niobium single crystals containing normal conducting Nb₂N-precipitates were prepared. In the present paper the authors report on the sample preparation and discuss the results of different experimental techniques (e.g. magnetization measurements, optical and electron microscopy, neutron small angle scattering) used to characterize the metallurgical state of the niobium single crystals. (Auth.)

[en] Investigations of the microstructure and the magnetic domain structure are necessary for the understanding of the coercivity of magnetic materials. Transmission electron microscopy has been used to study the new-highest-coercivity magnetic materials based on cobalt-rare earth intermetallic compounds, Fe-Cr-Co and Mn-Al-C alloys. In single-phase cobalt-rare earth and Mn-Al-C magnets the coercivity is controlled by nucleation of reverse domains at low anisotropy defects and by domain wall pinning at grain boundaries. In precipitation-hardened cobalt rare earths the coercivity is controlled by the pinning of domain walls by a continuous, cellular precipitation structure of a second ferromagnetic phase. The shape anisotropy of the FeCo-rich phase is the dominant factor in determining the coercivity of Fe-Cr-Co magnets. (Author)

[en] A transition electron microscope study of several precipitation hardened cobalt rare earth magnets has been undertaken. The magnets were in peak aged condition and varied in the chemical composition. The studies reveal a fine cellular microstructure. The shape and size of cells depend on the heat treatment and the alloying elements. The cell interiors consist of at least two plate-shaped 17:2 phases and are surrounded by a 5:1 boundary phase. The replacement of zirconium with hafnium does not alter the cellular morphology and also leads to a high coercivity. The coercive force is strongly influenced by the shape and size of the cellular structure as wll as by the lattice misfit between the 5:1 and 17:2 phases. The influence of the microstructure on the coercivity is discussed. (orig.)