C. D. Graham

Low−field magnetic properties of ferromagnetic amorphous alloys

The low−field magnetic properties of some amorphous magnetic alloy ribbons have been measured. The as−prepared specimens have low coercive field but rather low remanence. The application of elastic stress greatly increases the remanence, and can also decrease the coercive field. Some of the improvement due to stress can be made permanent by annealing under stress. These alloys should be useful in various magnetic devices.

Physical origin of losses in conducting ferromagnetic materials (invited)

The physical origin of losses in conducting ferromagnetic materials is the production of heat by the flow of eddy currents in the material. The eddy currents are generated by the voltages caused by changes in the magnetic induction. This statement, although true, is not very helpful in calculating or predicting the actual magnitude of the losses. For such a calculation, we need a detailed knowledge of the mechanism of magnetization reversal. The present standing of efforts to predict losses is briefly reviewed and discussed.

Domain Walls in Ferromagnetic Dy and Tb

The spin structure and energy of ferromagnetic domain walls in Dy and Tb have been calculated, using an iterative method which takes into account exchange interactions, magnetocrystalline anisotropy, and magnetoelastic anisotropy. The domain walls are found to be very thin (less than 20 atom layers) and to have relatively high energy (∼10 erg/cm2), as compared to the ferromagnetic transition metals. An intrinsic coercive force for wall motion is predicted for these very thin walls; it is analogous to the Peierls‐Nabarro force on a dislocation, and is estimated to be of the order of 1 kOe for Dy and 30 Oe for Tb at absolute zero.

Mechanism of texture formation by hot deformation in rapidly quenched FeNdB

The development of crystallographic texture in rapidly quenched Fe14Nd2B has been investigated by hot deformation. The method was to catch the process in a state of partial completion, and then use transmission electron microscopy to examine the structure. The degree of texture formation was determined by x‐ray diffraction and by magnetic measurements, and the hardness and the anisotropy in hardness were measured up to 600 °C. It was concluded, in agreement with others but with additional evidence, that preferential growth of favorably oriented grains during plastic deformation produces the texture. The nature of the plastic deformation remains unclear, since no dislocations are observed in Fe14Nd2B. It was found that when samples are compressed at temperatures near 600 °C under low stresses for long times, they become Nd rich at the bottom, presumably because of flow of the Nd‐rich liquid phase under the influence of gravity. In such samples, plastic deformation and crystallographic orientation occurs pr...

Kinetics of formation of induced magnetic anisotropy in a zero‐magnetostriction amorphous alloy

The kinetics of formation of magnetic annealing anisotropy have been measured in the zero‐magnetostriction amorphous alloys (Fe0.063Co0.937)75Si15B10 over the temperature range 165–380 °C by analysis of torque curves on single disk samples. Only at temperatures above 330 °C was it possible to reach equilibrium saturated values of the anisotropy in reasonable times (less than 20 h). By assuming that the equilibrium saturated value of the induced anisotropy is linear with temperature, it is possible to deduce an activation energy for the magnetic annealing process in a well‐annealed sample. The value is about 2.0±0.1 eV. This is considerably higher than the value of 1.4 eV found by Luborsky or 1.7 eV reported by Chambron and Chamberod for Fe40Ni40P14B6. The higher value in this work is presumably due to the relatively high glass transition temperature and crystallization temperature of the FeCoBSi alloy. The kinetic data reveal the existence of range or relaxation times, which can be analyzed assuming a log...

Fe‐B‐C amorphous alloys with room‐temperature saturation induction over 17.5 kG

Amorphous alloys of Fe86B14−xCx (5⩽x⩽7) were found to have room‐temperature saturation induction approaching 18 kG after appropriate heat treatment. The alloys possess excellent soft‐magnetic properties with the ac loss less than 0.5 W/kg at 17 kG and 60 Hz. It is expected that the application of these alloys to power transformers will produce very large savings of energy.

An investigation of the Nd‐rich phases in the Nd‐Fe‐B system

Etude par microscopie electronique en transmission, diffraction de rayons X et spectrometrie Auger des structures cristallines et des compositions des phases riches en Nd dans le systeme Nd−Fe−B. Etude des transformations de phase accompagnant le frittage de la poudre aux hautes temperatures

Statistical analysis of the orientation of sintered SmCo 5 magnets

A statistical model is developed to describe the orientation of particle easy axes with respect to the alignment direction in sintered SmCo 5 magnets. The model can be used to describe the three-dimensional orientation distributions measured by Swift et al [1]. using x-ray techniques, and with appropriate modification, the two-dimensional orientation distributions measured metallographically by Martin [2]. The distribution is described by a single parameter β, analogous to the standard deviation of a Gaussian distribution. For a given β, the model predicts the ratio of remanence to saturation and also the shape of the magnetization curve measured in decreasing fields when the field is applied perpendicular to the alignment axis. The effective anisotropy and the value of β can be determined by comparison of experimental and calculated curves.

Amorphous alloys with improved room-temperature saturation induction

The application of magnetic amorphous alloys in power transformers could produce significant savings of energy. Currently, the major disadvantage of amorphous alloys is their relatively low room-temperature saturation induction. We have attained a saturation reduction of 17.3 kG in heat-treated amorphous Fe 86 B 8 C 6 . By the addition of 1% cobalt, this can be brought up to 17.5kG for Fe 86 Ni 3 Co 1 B 5 C 5 Si 2 ; however, the thermal stability of this alloy is inferior to the Fe 86 B 8 C 6 alloy. These results make the use of amorphous alloys in power transformers much more attractive than before.

X-ray determination of alignment in FeNdB magnets

The preferred orientation or crystallographic alignment of several NdFeB magnets has been studied by x‐ray diffraction. A simple diffraction geometry was used, corresponding to a single line section across a pole figure. The (006) reflection was found to be the most useful for this purpose. Some practical problems of sample preparation and reproducibility are discussed, and results are presented. As expected, the magnetic properties of the magnets improve with the degree of alignment, although the dependence is relatively weak. Extrapolation suggests that significant further increases in magnet properties could be achieved by better crystallographic alignment.