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Transmission electron microscopy has been used widely to characterize the complex multiphase microstructure of Nd 2 Fe 14 B based permanent magnets. The grain size of the magnets strongly depends on the processing technique. Our study of sintered magnets revealed two types of grain boundaries: one containing no intergranular phase between hard magnetic grains and one composed of nonmagnetic Nd-rich phases. In doped sintered magnets the dopant is dissolved in the hard magnetic φ-phase. In the case where the solubility of the dopant is low at the sintering temperature (Nb, Mo, Zr), precipitates are formed within the φ-phase. Dopants also form new intergranular phases and influence the wetting of the liquid phase and the smoothness of the surface of the φ-grains during sintering and therefore affect the coercivity.

By means of electron irradiation the amorphous state can be produced in quasicrystalline and crystalline Al14 at% Mn. The transitions between these three phases are studied in situ in a high-voltage electron microscope. The behaviour of the quasicrystalline phase exhibits features distinctly different from those of the crystalline phase. Under certain conditions the phase transition quasicrystalline–amorphous is reversible and the quasicrystalline phase develops from the amorphous state. From the temperature dependence of the transformation kinetics conclusions can be drawn on the temperature dependence of atom transport in the phases investigated. Mit Hilfe von Elektronenbestrahlung last sich in quasikristallinem und kristallinem Al14 at% Mn der amorphe Zustand einstellen. Die Ubergange zwischen diesen drei Phasen werden in situ in einem Hochspannungselektronenmikroskop untersucht. Die quasikristalline Phase zeigt dabei ein Verhalten, das deutlich verschieden ist von dem der kristallinen Phase. Der Ubergang quasi-kristallin–amorph kann reversibel gefuhrt werden, d. h. unter bestimmten Bedingungen bildet sich aus dem amorphen wieder der quasikristalline Zustand. Aus der Temperaturabhangigkeit der Kinetik der Phasenubergange last sich auf die Temperaturabhangigkeit des Atomtransportes in den untersuchten Phasen schliesen.

The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x = 0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets we found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe, Al)2, phase between the hard magnetic grains. Our analytical TEM study revealed that in “Al2O3-doped” magnets the crystal structure of the Nd-rich intergranular phase partly changes from fcc (a = 0.52 nm) to hep (a = 0.39 nm, c = 0.61 nm), whereas the content of iron simultaneously decreases from 5–10 at.% to 1.5–4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2 (B, O)x, phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.

By means of the magneto-optical Kerr effect the domain configuration in Co5Sm-crystals is investigated in dependence on the applied magnetic field. The observed change of the domain structure is interpreted in terms of a micromagnetic theory for the magnetization curve of uniaxial single crystals. The displacement of domain walls took place at an initial field of 265 Oe which is interpreted as the intrinsic coercive field due to the Peierls potential and randomly distributed lattice defects. The density of the interaction energy per extension of the wall is determined to be in the case of a rigid wall. The nucleation of reversed domains is observed in the phase boundary between precipitate and matrix. Furthermore precipitates in grain boundaries are found to act as sources of nucleation centres. These results are interpreted by the nucleation of reversed domains in regions of low crystal anisotropy or of irregular precipitate-surface. Mittels des magnetooptischen Kerreffekts wird die Domanenstruktur in Co5Sm-Kristallen in Abhangigkeit vom auseren Magnetfeld untersucht. Die beobachtete Anderung der Domanenstruktur wird durch eine mikromagnetische Theorie fur die Magnetisierungskurve eines einachsigen Einkristalls interpretiert. Die Bewegung der Domanenwande tritt erst ab einer Feldstarke von 265 Oe ein. Dies entspricht einer inneren Koerzitivfeldstarke, die durch das Peierlspotential und statistisch verteilte Gitterfehler hervorgerufen wird. Die Dichte der Wechselwirkungsenergie pro Ausdehnung der Wand wird fur den Fall einer ebenen Wand als bestimmt. Die Nukleation der Domanen wird im Phasenubergang zwischen Ausscheidung und Matrix beobachtet. Des weiteren konnen Ausscheidungen in Korngrenzen als Nukleationszentren nachgewiesen werden. Diese Ergebnisse werden durch die Nukleation von Domanen in Bereichen niedriger Kristallanisotropie oder ungleichformiger Ausscheidungsoberflache interpretiert.

Controversial results on the microstructure of cast Nd80Fe15B5 alloys have been reported. Our investigations revealed a microstructure consisting of three phases: the hard-magnetic Φ phase, the platelet-shaped boride phase (ρ) Nd5Fe2B6, identical with the one found in Nd20Fe73.5B6.5 sinter magnets which is embedded within the fcc-Nd phase. A new phase with a Nd : Fe r 1:1.1 was found.

The different microphases of high coercivity (Co, Fe, Cu, Zr)7.5Sm permanent magnets have been studied and characterized by means of high-resolution electron microscopy. From lattice-fringe images of the cellular microstructure the misfit of the crystal lattice parameter between the coherent cell boundary phase and the cell interior phase is determined. It is shown that the platelet phase within the cell interiors consists of a hexagonal Co17Sm2 layer.

The coercivity of Nd-Fe-B sintered magnets has been improved by Al additions. To study the microstructural effect of Al addition, two types of investigation were formed: (1) the change in the wetting behavior of the liquid phase, at the sintering temperature, was studied by measurements of the wetting angle; and (2) the microstructural changes resulting from Al additions were studied by transverse electron microscopy assisted by energy dispersive X-ray analysis. A systematic change was detected that depended on the kind of Al addition, i.e., metallic or as Al/sub 2/O/sub 3/. >

The magnetic domain structure and microstructure of several Co-Sm magnet alloys were examined by transmission electron microscopy. This study reveals that the investigated single-phase magnets exhibit a low defect density within the grains. The coercivity is determined by the nucleation of reverse domains at soft magnetic inclusions. Precipitation - hardened magnets contain a fine-scale precipitation structure. From the wavy nature of the domain walls we conclude a strong pinning at the precipitates.

The microstructure of sintered Nd-Fe-B magnets is studied by analytical electron microscopy. The presence of Fe-rich precipitates was first found in magnets showing a small kink in the demagnetization curve, which is an evidence for soft magnetic nucleation centers for reversed magnetic domains within the magnet. alpha -iron precipitates occurred outside as well as within the hard magnetic 2:14:1 grains and were also found in other commercial-grade magnets with a nominal composition close to Nd15-Fe77-B8. >

Various sintered Nd 15 Fe 77 B 8 permanent magnets supplied by different producers have been examined by analytical electron microscopy. An identical microstructure was found in all of the different magnets. Three phases were detected by means of high resolution electron microscopy, electron diffraction and x-ray microanalysis. Besides the hard magnetic boride phase Nd 2 Fe 14 B, a soft magnetic boride phase close to Nd 2 Fe 7 B 6 , and a Nd-rich sintering aid phase (d.h.c.p. structure) were identified. The Nd-rich phase preferentially occurs along grain boundaries as a thin layer with about 10 nm tickness. The soft magnetic phases determine the magnetization reversal and limit the coercivity of sintered Nd-Fe-B magnets.

Sintered Nd15-Fe77-B8 magnets contain a multiphase microstructure. Our analytical transmission electron microscope study reveals that the Nd-rich phase, which is an essential part of the liquid phase sintering process can be divided into at least 4 subtypes with different Nd:Fe-ratios. Impurities of the raw material such as Nd-oxides and Nd-chlorides are randomly found in magnets, partly in the form of small inclusions up to 500 nm diameter within 2:14:1-hard-magnetic grains and partly in the form of large grains up to several microns diameter. As consequence of this analytical study a high concentration of boron vacancies as well as iron vacancies, especially in grain boundary regions is proposed. We have found that the degree of continuity of the intergranular Nd-rich phase is proportional to the intrinsic coercivity of the magnet. The intrinsic coercivity of sintered Nd-Fe-B magnets is determined by the nucleation of reversed domains and by the expansion of the reversed muclei, which is hindered by the non-magnetic Nd-rich oxide grain boundary layer phase.

Microstructures of Nd15−xDyxFe77B8 prepared by alloying with Dy, and by using Dy2O3 as a sinl'ken adidive, have been determined using electron microprobe and transmission electron microscopy. The results have shown a higher Dy concentration near the grain boundaries of the 2–14–1 phase for magnets doped with Dy2O 3, as compared to the Dy-alloyed magnets. A two-step post sintering heat treatment was also studied for the two systems. The resultant concentration gradient of Dy in the 2–14–1 phase of the oxide-doped magnets is explained by the reaction of Dy2O3 with the Nd-rich grain boundary phase and its slow diffusion into thg 4–14–1 phase. Increased Dy concentration near the grain boundary is more effective in improving the coercivity, as domain reversal nucleation originates at or near this region.

Transient magnetization states during switching are investigated numerically in thin granular square shaped nanoelements (100/spl times/100 nm/sup 2/) with uniaxial (Co-hcp), cubic anisotropy (Co-fcc) and zero anisotropy (Ni/sub 80/Fe/sub 20/) with 10 nm grain size and a thickness of 10 nm and taking into account a random orientation of the grains using a hybrid finite-element/boundary-element model. In-plane switching dynamics are calculated for external fields with a constant sweep rate of 0.02 and 2.0 J/sub s//(/spl mu//sub 0//spl middot/ns). The switching time and critical field strongly depends on the Gilbert damping parameter and sweep rate. Largest switching times and fields were found for the Co thin film element with uniaxial anisotropy, such as 5 ns and 120 kA/m for 0.02 J/sub s//(/spl mu//sub 0//spl middot/ns) and 0.1 ns and 245 kA/m (/spl alpha/=0.02) and 329 kA/m (/spl alpha/=1.0) for 2 J/sub s//(/spl mu//sub 0//spl middot/ns), respectively. Depending on the sweep rate the fastest in-plane switching occurs in the granular cubic Co- and permalloy-thin film elements (

We perform multi-scale finite element simulation of the write process in perpendicular media. The Landau-Lifshitz Gilbert equation is solved simultaneously for the head, the data layer, and the soft under layer during the motion of the head. All magnetostatic interactions between head, data layer and soft underlayer (SUL) are concurrently taken into account. This fully integrated recording model enables a detailed analysis of the head field as seen by the media grains. The effects of the media permeability onto the saturation of the soft underlayer and the head pole tip are an inherent part of the simulation model. In this paper, we focus on the time dependence of the different contributions to the total head field, which is composed of the field generated by the pole tip, the field generated by the head, and the self-demagnetizing field of the data layer. Besides the magnetic properties, the only input for the simulations is the current profile for the coil excitation and the head velocity. The head field dynamics is calculated from the induced magnetization processes within the head, the data-layer, and the soft underlayer. Domain wall motion within the yoke of the head, vortex motion within the pole tip of the head, and large-area magnetization processes in the soft underlayer cause a lag of the head field behind the current.

Domain processes associated with exchange bias in IrMn/NiFe are investigated using a micromagnetic approach. The model give quantitative estimates of the bias field and the coercivity for antiferromagnetic/ferromagnetic bilayers with fully compensated interfaces. The numerically calculated domain processes are compared with those observed in transmission electron microcopy studies of exchange biased bilayers.

EELS (electron energy loss spectrometry) in the transmission electron microscope (TEM) was used to determine the composition of a nanocrystalline magnetic specimen. The relative amounts of the hard magnetic phase Nd 2 Fe 14 B and the soft magnetic phase Fe 3 B at the point of measurement was measured by standard EELS quantification. In order to determine the structure of Fe 3 B present, the fine structure of the boron K -ionisation edge was analysed. Comparison of the experimental spectra with simulations of the fine structures based on the TELNES extension of the WIEN97 program package, a full potential linearised augmented plane wave approach to the calculation of electronic structure in crystals, shows that the tetragonal form of Fe 3 B is predominant.

Precipitation‐hardened SmCo 2:17 sintered magnets contain a multiphase, cellular microstructure,1 which is determined by nominal composition and heat treatment parameters. A correlation between microstructure and coercivity has been shown by transmission electron microscopy (TEM).1,2 Magnets with different samarium content were investigated. In magnets with iHc

This paper is considered a first approach to detecting the domain configuration of coated Si–Fe sheets by computer-controlled field scanning. A topogram of the domains is plotted, and the physical origin of the detected field components is discussed. Also, stray field topograms of magnetized sheets are presented. These indicate that the field intensity cannot be associated with the angle of misorientation of an individual grain.