摘要:

The results obtained in part I are interpreted in terms of the viscosity field arising from independent processes of directional ordering for magnetic defects dispersed in the amorphous structure and interacting with the magnetization vector. A specific model is developed in order to take into account the changes in the ordering kinetics induced by the periodic magnetization rotations described in part I. This model, however, requires that the magnetic induction remain constant during the whole measurement; as a consequence, the model’s predictions cannot be directly compared with the experimental results, obtained instead at constant applied field. This difficulty is overcome by deriving a general relationship between the magnetic‐induction decay and the viscosity field kinetics for an arbitrary number of half‐periods of the square‐wave field. The agreement of our theory with the experimental results turns out to be quite satisfactory. As consequence, the ordering processes responsible for the magnetic aftereffect in amorphous ferromagnets may be described as essentially uncorrelated.

ISSN:0021-8979    

DOI:10.1063/1.346153

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The relationship between the magnetic properties and microstructures of flakes of a Nd15Fe77B8alloy produced by twin‐roller quenching was studied. Flakes produced at low to intermediate roller speeds (1.4–8 m/s) showed a dendritic structure of Nd2Fe14B oriented normal to the chilled surface, while flakes produced at higher roller speeds showed fine, equiaxed Nd2Fe14B grains. The flakes with a dendritic structure were found to be magnetically anisotropic and showed a high‐energy product (BH)max(15.2 MGOe) in the direction perpendicular to the chilled surface. The flakes that had fine equiaxed grains were magnetically isotropic. The maximum coercivity of the flakes exceeded 20 kOe. The microstructural transition from columnar dendrites to equiaxed grains is explained in terms of morphological changes in the solidification of undercooled melts. Optimization of twin‐roller quenching parameters for the production of desirable microstructures in Nd‐Fe‐B magnets is discussed.

ISSN:0021-8979    

DOI:10.1063/1.346154

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Various crystallographic textures of Co‐alloy/Cr bilayer thin films are discussed based on microdiffraction and selected‐area diffraction (SAD) results. In order to understand the origin of the crystallographic texture of the Co thin films, the orientation relationships between the Co and Cr grains were determined by the electron microdiffraction technique. From this information, we suggest that the {110} Cr underlayer texture may not necessarily be required to obtain the highest in‐plane coercivity in Co films. In order to evaluate the crystallographic texture of the film by SAD patterns, normalized intensity of SAD patterns for various thin‐film textures have been calculated. Using these calculations, we interpret the SAD patterns taken from various Co and Cr thin films.

ISSN:0021-8979    

DOI:10.1063/1.346155

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The ferromagnetic Heusler alloy Pd2MnSn shows large reduction in magnetization by cold working, without any appreciable change in the Curie temperature. In order to clarify the relationship between the reduction and the defect structure in Pd2MnSn, transmission electron microscopic observation, high‐resolution neutron powder diffraction, and magnetization studies have been performed. In the deformed Pd2MnSn sample, dislocations are distributed inhomogeneously and form a cell structure. In the cell walls, a large amount of antiphase domain boundaries exist. A method of Rietveld refinement has been proposed for analyzing the powder neutron diffraction patterns of the cold‐worked sample, where all the contributions of defects (size, strain, and antiphase domain boundary) and the instrumental resolution to each reflection line are expressed in terms of Fourier coefficients, and inverse Fourier transforms of those product represent the calculated profile which is used for least‐squares refinement. Analyzing the experimental data with the method proposed, it is concluded that the reduction in magnetization in the deformed Pd2MnSn is due to an increase in the number of small antiphase domains which couple antiferromagnetically to each other.

ISSN:0021-8979    

DOI:10.1063/1.346128

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The change in compositional distribution of sputtered Co‐21 at. % Cr films is investigated as a function of substrate temperature using thermomagnetic analysis. As the substrate temperature increases from 50 to 400 °C, the compositional inhomogeneity progresses causing compositional separation through two stages: in stage I (substrate temperature = 50–200 °C), there occurs a drastic compositional separation into a ferromagnetic Co‐rich component (10–13 at. % Cr, 45–50 vol %) and a paramagnetic Cr‐rich component (30–40 at. % Cr, 30–40 vol %) in a hcp structure; in stage II (substrate temperature =300–400 °C), &sgr; phase precipitation seems to proceed competing with homogenization while the compositionally separated state still exists. At both stages, components with a total volume fraction of 10%–25% and compositions close to that of the film average are observed to remain. The compositional separation is recognized in compositional microstructures revealed by selective chemical etching. A two‐phase separation due to the effect of magnetic transition is discussed as a possible origin of this compositional separation.

ISSN:0021-8979    

DOI:10.1063/1.346129

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

CoNbZrN amorphous films were found to exhibit soft magnetic properties when deposited by ion beam sputtering or dc magnetron sputtering. In contrast to CoNbZr films they crystallize into a microcrystalline phase. Good magnetic softness is maintained during heat treatments up to 700 °C. It was found that the crystalline phase includes Co and NbN fine grains. The results of magnetostriction and electrical resistivity measurements suggest that an initial stage of crystallization starts at relatively low temperatures.  

ISSN:0021-8979    

DOI:10.1063/1.346130

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper discusses the principles of topographic influence on magnetic force microscopy (MFM) response. We present in a theoretical quantitative way the effect from some chosen topographic features on MFM signal and conditions, which should be fulfilled to detect such an effect. We considered two cases of magnetization direction inside the sample, perpendicular and parallel to the surface.

ISSN:0021-8979    

DOI:10.1063/1.346131

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have observed a very interesting feature in the mid‐infrared region of copper‐doped semi‐insulating liquid encapsulated Czochralski grown GaAs at liquid helium temperature. After gettering copper using backside mechanical damage, the transmittance of this particular feature became much weaker. The first absorption feature occurs at 1182 cm−1(0.147 eV), the second at 1460 cm−1(0.181 eV), and the third at 1750 cm−1(0.217 eV), which is a transition of an electron from the valence of three copper levels. This electronic mode absorption allows us to obtain information about the activation energies of deep‐level impurities like Cu and their relative concentration after each process. This electronic mode absorption at multilevels of Cu in GaAs is proposed for the first time using the Fourier transform infrared technique to detect deep‐level metal impurities in GaAs.

ISSN:0021-8979    

DOI:10.1063/1.346132

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A Raman study has been performed, under resonant conditions, on a GaAs bevelled‐edge layer grown on a Si substrate to characterize the optical and crystalline properties of the epilayer near the interface. According to the geometrical characteristics of the sample, a theoretical expression for the Raman intensities profile has been established and compared to the experimental data. This fitting procedure enables us to investigate the absorption coefficient of the GaAs layer due to the disorder‐induced softening of theE1edge. A quantitative analysis of the lattice disorder has been carried out on both longitudinal and transverse optical modes by studying the Raman line‐shape evolution versus the laser spot position on the bevel edge. From this study, we have followed the recovery of the crystalline quality of the epilayer while going away from the interface, and evaluated the ‘‘Raman thickness’’ of the dislocated layer. Using the spatial correlation model as a relationship between the disorder amount and the outcoming effects on the Raman line peaks, we have estimated the dislocation density at the heterostructure interface.

ISSN:0021-8979    

DOI:10.1063/1.346133

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new approach for signal processing and parameter measurement is reported. This new concept uses Bragg cells and photorefractive materials in a time‐integrating structure to compute correlation values. It uses the same Bragg cell for both computing correlations and performing the final signal weighting and summation. The resulting structure not only provides a powerful signal processing method, it leads to a new measurement technique which is useful in measuring the characteristics of photorefractive materials. This latter application is the subject of this paper. Direct measurement of the photorefractive grating phase is demonstrated and the results are used to show the dependence of grating phase on intensity. Also a method for generating moving gratings electronically (without moving mirrors) is proposed and demonstrated. Amplitude and phase measurements are reported for the fringes produced by such an electronically generated moving grating.

ISSN:0021-8979    

DOI:10.1063/1.346134

出版商:AIP    

年代:1990

数据来源: AIP