Field Distribution Curves Research Articles

2相ステンレス鋳鋼におけるフェライトの相分離過程のメスバウアー分光測定

Duplex stainless steels become brittle at medium temperatures, owing to the phase decomposition of a ferrite into a Cr-rich α′ phase and an Fe-rich α phase. A cast CF3M duplex stainless steel containing 25% volume fraction of ferrite was aged at 723 K for time periods up to 10000 h to investigate the phase decomposition mechanism and to evaluate the composition of the decomposition products using Mössbauer spectroscopy at room temperature. The half width of the internal magnetic field distribution curve estimated from the experimental Mössbauer spectra increases in the initial stage of aging, suggesting compositional fluctuation due to spinodal decomposition. The ferrite phase finally decomposes into the Fe-rich α and Cr-rich α′ phases after prolonged aging. The composition of the Fe-rich α phase is estimated to be Fe-11 at%Cr-5 at%Ni by numerically analyzing the internal magnetic field distribution based upon the local environmental effect of solute atoms on the central Fe nucleus. The result is consistent with the one previously obtained by atom-probe analysis. The isomer shift of 57Fe in the α′ phase is estimated to be −0.114±0.002 mm/s at room temperature by decomposing an overlapped paramagnetic absorption peak into component peaks. The Cr content of the phase is estimated to be about 85 at% by plotting the isomer shift on an experimental isomer shift versus Cr content diagram.

Effects of several kinds of anisotropy on the coercivity behaviors of iron oxides

Coercivity behaviors of iron oxides during phase changes between Fe3O4 and γ-Fe2O3 for granular powders and continuous thin films, which can be interpreted in a unified framework by an intermediate product hypothesis, are investigated. There exists a critical value ccr of Fe3O4 concentration for different samples. The intermediate product Fe3−zO4 in oxidation and reduction processes is a mixture of two phases when Fe3O4 concentration c is smaller than ccr; but it may exist in the form of a homogeneous solid solution (single-phase) (Fe3O4)1−x(γ-Fe2O3)x when c is larger than ccr. The difference in lattice constants will produce a tensive stress (σ≳0) on γ-Fe2O3 and compressive stress (σ<0) on Fe3O4 at interfaces. Superposition of a positive stress anisotropy on the easy axes 〈111〉 of magnetocrystalline anisotropy for Fe3O4 and on the easy axes 〈110〉 for γ-Fe2O3 will cause an increase in the coercivity Hc for spherical particle and thin film samples. The coercivity behavior of our acicular particle sample is contrary to that of thin film and spherical particle samples. Also, the switching field distribution curve showed a peak near c=0.4. There always exist some two-phase intermediate compounds in Fe3−zO4 due to the incomplete reaction of single domain particles. The decrease in coercivity of acicular particles is affected by the shape anisotropy related to changes in effective particle sizes.

Mössbauer effect of Fe-rich FeZr amorphous alloys

AC susceptibility, X AC and Mössbauer spectra have been measured for Fe 100− x Zr x amorphous alloys ( x = 8−12 at.%). The magnetic phase diagram estimated from AC susceptibility measurements shows the re-entrant spin glass state in all of the present specimens, and the hyperfine field distribution curve P( H hf) at 4.2 K is very broad. These results suggest the magnetic heterogeneity in the specimens. The anomalous increase of average hyperfine fields 〈 H hf〉 below T sf(〈 H hf〉) may be attributed to the freezing of transverse components of spins.

メスバウアー分光法によるFe-28Cr-5Ni合金中の2相分離相の組成決定

The effect of Ni on the internal magnetic field and the isomer shift of 57Fe in Fe-Cr alloys containing 3 to 14 at%Cr and 70 to 90 at%Cr were examined at room temperature by Mössbauer spectroscopy. A model Fe-28%Cr-5%Ni alloy was aged up to 5000 h at 723 K to investigate the phase decomposition of ferrite in a commercial duplex stainless steel. The alloy finally decomposed into a Cr-rich phase (α′) and an Fe-rich phase (α) after aging. A paramagnetic absorption peak due to the α′ phase has an isomer shift of −0.110 mm/s at room temperature. The value corresponds to a Cr content of 85(±1)at%Cr. The composition of the α phase was estimated to be 11(±1)at%Cr from the average internal magnetic field and the internal field distribution curve. The result of α phase was consistent with a result obtained by atom probe microanalysis. The latter underestimated the Cr content of the α′ phase in comparison with the Mössbauer effect.

M?SSBAUER EFFECT OF VAPOR QUENCHED Fe-Pd ALLOYS

M?ssbauer spectra were taken at 4.2 K and 290 K for the bcc and fee Fe1-xPdx alloys produced by vapor quenching. The hyperfine interaction parameters and hyperfine field distribution curves were obtained with spectrum fitting method. With increasing x, the average hyperfine field, Hhf increases in bcc Fe1-xPdx alloys, while Hhf decreases in fee alloys. The concentration dependence of Hhf can be explained by using a semi-empirical formula.

Mössbauer isomer shift and hyperfine fields of ordered and disordered Fe3Al alloys

The Mossbauer technique was used to measure the hyperfine magnetic field and isomer shift of57Fe nucleus in the ordered and disordered Fe3Al alloys. The Mossbauer spectra were analyzed to yeld the hyperfine magnetic field distribution curves. A linear correlation has been revealed between the average hyperfine field and the average number of Al atoms in the first two nearest neighbour shells of57Fe nucleus,N Al, for both ordered and disordered alloys. The measured values of the mean isomer shift agree very well with the values expected from the Miedema-Van der Woude model.

M�ssbauer studies of a-Fe74Co10?xCrxB16 alloys

Fe57 Mossbauer spectroscopy has been employed to study hyperfine interactions in melt-spun a-Fe74Co10−xCr x B16 (x = 0, 2.5, 5, 7.5 and 10) ribbons. The Curie temperature and the effective hyperfine fields observed for the spectra at 80 K show a systematic fall with increasing chromium content. Increasing chromium content also brings about a change in the orientation of the magnetization axis in that it comes closer to the direction of γ-ray propagation. The temperature dependence of hyperfine fields in a-Fe74Co5Cr5B16 alloy is accounted for using the existing theoretical models. The field distribution curves show a temperature dependence, while the e.f.g. distribution evaluated from the paramagnetic doublet spectra aboveTc are temperature independent. The spin-wave coefficients B (B3/2) and C (C5/2) and the critical exponent, β, were determined and their significances explained.

M?SSBAUER STUDY OF AMORPHOUS Fe-Ni-MET FERROMAGNET

In this paper, the M?ssbauer spectra of amorphous Fe81-xNixSi3.5B13.5C2 (x = 5, 10, 15, 20, 25, 30, 35) alloys and crystalline Fe50Ni50 are studied at room temperature and under external magnetic field. The hyperfine interaction parameters and hyperfine field distribution curves were obtained with the fitting spectrum method. The results indicated that there are two magnetic states of iron atom and Inver-like characteristic in amorphous Fe-Ni-Met alloys. Anomalous phenomena at about 15 at % Ni in Fe-Ni-Met alloys was revealed. It was suggested chat the conditions of external magnetic field and low temperature have the similar effect on the ordering of magnet. In the sometime, the mechanism of hybridization of the Fe 3d hand with the metalloid valence orbitals and the electron tranfer between transition metals was used to explain the experimental results for the amorphous transition metals (TM)-metalloid (Met) alloys.

Computation of Electric Fields and Study of Optimal Corona Suppression for Bushing-Type Insulators

Using the Runge-Kutta and Newton-Raphson methods, the electric fileds on the bushing-type insulator surface covered partly by a corona-suppression semiconductor coating with a field-dependent resistivity have been computed for semiconductors having various resistivityfield ield (p-E) characteristics. The field distribution along the insulator surface is strongly dependent on the p-E characteristic and the extension of the semiconductor coating as well as the frequency of the operating voltages. By assigning the highest field along the insulator surface to be the critical field for the onset of corona discharges (or the breakdown strength of air or other medium), the corona inception voltage of the insulators can be evaluated easily. Thus, by the comparison of the field distribution curves, it is easy to determine the type of the p-E characteristic and the extension of the semiconductor coating for optimal corona suppression. For bushing-type insulators, the computed results show that the semiconductors with p = poexp(-BE) or p * pO[2 - exp(aE)], where po, and a are constants, could give optimal corona suppression. The optimal choice depends on the physical parameters of the insulator, the extension of the semiconductor coating and the frequency of the operating voltages, and therefore the constants pO and or a have to be determined for individual cases. In general, for optimal al corona suppression po should decrease with increasing frequency and length of the insulator surface; and or a should increase with increasing length of the insulator surface.

NMR Investigation of Environment Effect in C-15 Type R1-xYxCo2 Pseudobinary Compounds; R=Pr and Ho

Curie temperature, magnetization and 59 Co NMR have been measured for the pseudobinary R 1- x Y x Co 2 (R=Pr and Ho). In the Pr system, the hyperfine field distribution curve of Co obtained from the NMR spectra shows a well resolved satellite structure, while in the Ho system no additional structure appears in the distribution curve by replacing Ho with Y. These results are discussed in terms of a local environment effect of Co atoms and of the metamagnetic nature of the onset of the Co moment. It is suggested that the Pr moment increases with increasing Y concentration becuase of a decrease in the crystal field.

Effect of Local Environment on Formation of Local Moments in bcc Fe–Cr Alloys–Mössbauer Study

The Mössbauer spectra of Fe–Cr solid solutions in the concentration range of 60–96 at%Cr were obtained at 5 K. These spectra were analyzed to yield hyperfine field distribution curves which are characterized by two distinct peaks. It has been revealed that an isolated Fe atom has a very small hyperfine field indicating a nonmagnetic character. The profiles of the hyperfine field distribution curves as well as the magnetic properties of the alloys, particularly near the critical concentration for ferromagnetism, are discussed on the basis of the local environment model.

Effect of local environment on formation of local moments in BCC Fe-V alloys: Mossbauer study

The Mossbauer spectra of BCC Fe-V alloys in the concentration range 40-80 at.% V have been obtained for both the ordered and disordered states. No broadening of the absorption line has been detected in an 80 at.% V alloy even at liquid He temperature indicating that the alloy is nonmagnetic. Broadening of absorption lines due to the magnetic hyperfine field has been observed for the alloys containing less than 70 at.% V. The spectra obtained at 5K were analysed to yield the hyperfine field distribution curves. It was found that the hyperfine field is notably reduced by atomic ordering. This change in hyperfine field is explained as the result of the change in Fe atomic moment which increases with increasing the number of Fe nearest neighbours. Profiles of the hyperfine field distribution curves are explained on the same basis. The dependence of the Fe atomic moment on the near-neighbour Fe composition is compared with the result of CPA calculations. Correlation between the lattice constant and the magnetic moment is discussed.

Mössbauer Study of bcc Fe-Al Alloys near the Critical Concentration

The Mossbauer spectra of Fe-Al alloys in the concentration range from 35 to 43 at% Al have been obtained at liquid He temperature. The spectra were analyzed to yield the hyperfine field distribution curves, which are characterized by two distinct peaks indicating the existence of two magnetic states of iron atoms, namely a magnetic state and a nonmagnetic state. It has been revealed that the fraction of the magnetic state, which was estimated from the intensities of two peaks, is comparable to the probability of finding an Fe atom having 4 or more than 4 Fe n.n. The average localized moment has been estimated from the intensity ratio. The average localized moment thus obtained is larger than the spontaneous moment. This fact indicates the existence of antiferromagnetically coupled spins. Correlation between the lattice constant and the magnetic moment is discussed.

Measurements of Magnetic Field of Magnetic Recording Head by a Scanning Electron Microscope

A mapping of the magnetic field distribution around the gap of a magnetic recording head has been carried out using a scanning electron microscope. The magnetic field distribution can be visualized by the distorted SEM image of a reference mesh set under the head. The field distribution curves this obtained are nearly elliptical in shape, and show a slight deviation from those obtained from Karlqvist's model.1) The range of the measurement is confined to an area 50 to 150 µm from the head surface. In this range the resolution of the mesurement system is less than 40 Oe.

Field Measurements on Magnetic Recording Heads

A method is described for measuring relative values of the magnetizing force along the path traversed by the recording medium in passing through a magnetic recording or reproducing head. Field-distribution curves obtained by this method are shown. A method for calculating the frequency response of a reproducing head from field-distribution data is presented, and results of calculations are compared with a measured frequency response. In the recording process, the important part of the field lies in the air gap. The highfrequency response depends on the sharpness of cutoff on the leaving side of the gap, and is independent of the shape on the approaching side.