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1.
We have studied similarity rules of quasistatic minor hysteresis loops for Fe and Ni single crystals in the wide temperature range from 10 to 600 K. Two similarity rules of MR*/Ma*∼3/4 and WR*/WF*∼1/6, were found in a medium field range where irreversible movement of Bloch walls plays a crucial role for magnetization; Ma*, MR*, WF*, and WR* are magnetization, remanence, hysteresis loss, and remanence work of a minor hysteresis loop. The similarity rules hold true, being almost independent of kinds of ferromagnets, applied stress, and temperature. The origin was discussed from the viewpoint of pinning effects due to dislocations as well as eddy current effects which become predominant at low temperatures for samples with low dislocation density.  相似文献   

2.
A novel method of analyzing the switching field distribution (SFD) and magnetic correlation length of perpendicular magnetic recording media that uses major and minor magnetization loops is proposed. By applying the analysis to a series of capped perpendicular media, we found that a thick capping layer with a low saturation magnetization effectively reduced SFD without rapidly increasing the magnetic correlation length. Transmission electron microscope observation suggests that the SFD is narrowed by the increased uniformity of intergranular exchange coupling via the thick capping layer. Evaluations of recording characteristics demonstrated a close correlation between narrower SFDs and improved recording performance. Reducing exchange coupling dispersion is a clear solution for improving the performance of recording media.  相似文献   

3.
ZnMnO nanoclusters were synthesized by the sol–gel method. The structural and magnetic characters were investigated. The XRD spectrum shows ZnMnO nanoclusters are hexagonal wurtzite structures and a small quantity of ZnMn2O4 phase is also present in the spectrum. The percentages of Zn and Mn elements in the ZnMnO nanostructure are 97% and 3%, respectively, which are induced from XPS data. EPR spectrum with g=1.9961g=1.9961 shows the signal of Mn2+. The magnetization curve measured at room temperature shows a hysteresis loop. XRD and XPS analyses prove that ferromagnetic ordering arises from ZnMn2O4 in all probability.  相似文献   

4.
5.
Temperature and field-dependent magnetization measurements on polycrystalline CeMnCuSi2 reveal that the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, Tc, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component (such as in a canted spin structure) is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce L3-edge X-ray absorption result shows that the Ce ions in this compound are nearly trivalent, very similar to that in the heavy fermion system CeCu2Si2. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) M(T) curves below Tc indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic-type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. The FM ordering of the Mn moments in CeMnCuSi2 is consistent with the value of the intralayer Mn–Mn distance RaMn–Mn=2.890 Å, which is greater than the critical value 2.865 Å for FM ordering. Finally, a magnetic phase diagram is constructed for CeMnCuSi2.  相似文献   

6.
Ba(Ti1−xFex)O3 ceramics (x=7, 30 and 70 at%) were prepared by solid-state reaction. All samples are single-phase with 6H-BaTiO3-type hexagonal perovskite structure. Mössbauer spectra show all Fe atoms to be present as Fe3+ in BaTiO3 lattice, occupying M1 octahedral and pentahedral sites. Room-temperature ferromagnetism is exhibited and saturation magnetization gradually decreases with increasing Fe content. The observed ferromagnetism is considered to be an intrinsic property of Ba(Ti1−xFex)O3, originating from super-exchange interactions between Fe3+ in different occupational sites associated with oxygen vacancies. The variation in magnetization with Fe content is related to the ratio of pentahedral to octahedral sites and oxygen vacancies.  相似文献   

7.
    
Itinerant ferromagnetic SrRuO3 with a Curie temperature TC = 160.7 K was prepared by a conventional solid reaction method. Its zero‐field‐cooled (ZFC) magnetization and field‐cooled (FC) magnetization were measured over a temperature interval from 5–180 K, in a sequence of applied fields up to coercivity. The major hysteresis loops were measured over a range of temperatures, which span the ordered phase. An empirical model was proposed to analyze the ZFC behaviors by means of coercivities at different temperatures. The calculated ZFC magnetization is consistent with the measured ZFC magnetization. Different ZFC magnetization behaviors were explained by using this model. The results indicate that the various ZFC behaviors originate from the comparison between the temperature dependence of FC magnetization and that of coercivity.  相似文献   

8.
Si1−xMnx diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si1−xMnx crystalline bulks. Hall effect measurements showed that annealed Si1−xMnx bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si1−xMnx bulks originated from the interaction between interstitial and substitutional Mn+ ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si1−xMnx DMS bulks.  相似文献   

9.
NdFeNbB with the additions of Dy2O3 and Sn permanent magnets have been attained by means of powder-blending technique, and their magnetic properties, temperature performance and microstructure were studied in this paper. The addition of just 2.0 wt% Dy2O3 or 0.3 wt% Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. Dy2O3 additions result in the increase in the Hci and temperature dependence due to the increase of Tc, formation of (NdDy)-rich phase and grain refinement of Φ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with Dy2O3 and Sn combined addition were found to be considerably improved. From the X-ray diffraction, SEM-EDAX studies and the thermo-magnetic study, the improved properties due to the solution of Dy and Sn to the Φ phase, the reduced Neff and the smaller Φ phase.  相似文献   

10.
Mg0.7Zn0.3SmxFe2−xO4 ferrites were prepared by the solid-state reaction method and were characterized by X-ray diffraction and magnetization measurements. A single spinel phase was obtained in the range 0.00?x?0.030.00?x?0.03. The lattice parameter was found to increase at x=0.01x=0.01 and then decreases up to x=0.03x=0.03, which may indicate a distortion in the spinel lattice. The saturation magnetization was found to decrease with the increase in x up to 0.04, due to the replacement of the Fe3+ ions by the Sm3+ ions.  相似文献   

11.
NiAlxFe2−xO4 and Ni1−yMnyAl0.2Fe1.8O4 ferrites were prepared by the conventional ceramic method and were characterized by X-ray diffraction, scanning electron microscopy, and magnetic measurements. The single spinel phase was confirmed for all prepared samples. A proper explanation of data is possible if the Al3+ ions are assumed to replace Fe3+ ions in the A and B sites simultaneously for NiAlxFe2−xO4 ferrites, and if the Mn2+ ions are assumed to replace Ni2+ ions in the B sites for Ni1−yMnyAl0.2Fe1.8O4 ferrites. Microstructural factors play an important role in the magnetic behavior of Ni1−yMnyAl0.2Fe1.8O4 ferrites with large Mn2+ content.  相似文献   

12.
The main subject of this work was to analyze magnetic losses of non-oriented soft magnetic materials, which are used in rotating machines like motors or generators, under the conditions of alternating and rotating magnetic flux. For this purpose a hexagonal rotational single sheet tester (HRSST) and a standardized 25 cm Epstein frame tester (EFT) were used, respectively. Since each HRSST sample represents only one random sample, whereas a stack of EFT samples represents a basic population of a production lot, a simple procedure is introduced to derive characteristic rotational loss data from EFT measurements and previously acquired loss factors.  相似文献   

13.
    
Positron‐annihilation lifetime measurements are used to study the influence of Mg17Al12 precipitates in mechanical properties of deformed magnesium alloys containing 9 wt% Al and 1wt% Zn. Deformations are performed at room temperature on untreated and thermal‐aged samples, and the response of the positron lifetime to the deformation degree is studied. Measurements reveal that changes in the average positron lifetime are very small on both samples. The slight increase of positron lifetime in deformed samples, seems to be related with the unfavourable orientation of Mg17Al12 precipitates in the magnesium matrix to produce work hardening, as it has shown by other authors through TEM observations. Further isothermal annealing experiments, on samples that are previously deformed, illustrate almost a complete recovery of the positron lifetime on untreated samples at ∼375 K and on age‐hardened samples at ∼433 K. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
The power losses of a non-oriented 3% Si-steel rolled to gauges between 0.05 and 2 mm and heat-treated thereafter have been measured under sinusoidal polarizations at frequencies between 15 Hz and 10 kHz. The losses were analysed using a loss separation model based on statistical theory. For the thick samples the skin effect caused the model to fail above a certain frequency, while for the very thin samples the model seems to describe the losses well at all frequencies studied.  相似文献   

15.
    
To reduce the core loss of grain oriented silicon steel, various metallurgical attempts have been made. The laser scribing reduces the core loss of 3% Si–Fe, because sub‐domains induced by scribing produce many active domain walls which reduce the eddy current loss. The profiles of ac hysteresis loop and core loss have been measured for samples oriented parallel and perpendicular to the [001] axis in (110)[001] grains of 3% Si–Fe before and after laser scribing. The observed ac hysteresis loop profiles have been analyzed in terms of domain reorientation under field. For the parallel and perpendicular samples, the reductions of core loss are 5.7% and 30.3% by laser scribing at the magnetic induction 1.3 T and magnetizing frequency 60 Hz. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
    
We studied the structural and magnetic properties of Ti1−xCoxO2 powder samples synthesized by the sol–gel method. In order to study the post annealing effect on the magnetic properties, the same precursor was annealed at 770 K for 5 h in air and in the pressure of 10−6 Torr. In the case of samples annealed in vacuum, enhanced ferromagnetism was observed at room temperature, while only paramagnetic behavior was observed in samples annealed in air. Moreover, the magnetization of the vacuum‐annealed sample sharply decreased around 650 K while measuring in air, but such decrease in the magnetization was almost absent while measuring in He gas up to 750 K. The structural studies showed dominant anatase and minor rutile phases in vacuum‐annealed samples, while an additional nonmagnetic CoTiO3 phase was observed in air‐annealed samples. We attribute the enhanced magnetization in the vacuum‐annealed sample to the oxygen deficiency which prevents the formation of non‐magnetic CoTiO3 complexes. It is also possible that the reduced oxygen environment can promote the clustering of Co‐rich clusters as evidenced by transmission electron microscopy in samples of x = 0.1, thus giving rise to an enhanced ferromagnetic behaviour. However, no direct observation of Co clusters in samples for x ≤ 0.05 was made. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
    
The profiles of ac hysteresis loops have been measured as function of the angle ϕ between H‐field and [001] axis in (110)[001] grain oriented 3% silicon‐iron. As ϕ increases, for ϕ ≥ 30° the loop changes into a wasp‐waisted shape with inflection points. The observed ac hysteresis loop profiles have been analyzed in terms of domain reorientation under field. The core losses in silicon‐iron are measured for various magnetizing angles with respect to the easy axis at magnetizing frequency 50 Hz and 60 Hz and at magnetic induction 1.3 T and 1.0 T. At magnetic induction 1.3 T, the core loss increased to near 70° and decreased at magnetizing frequency 60 Hz, but at 50 Hz this trend was different from 60 Hz and the core loss was monotonously increased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The paper presents an analysis of the losses due to irreversible Barkhausen jump of the 180° Bloch wall in the single-domain wall model. The field-intensity and current-density vectors at unit input were determined for a single instantaneous jump. The losses were calculated for the case of the wall moving sinusoidally. The Parseval formula was used at determining the losses, which made it possible to perform calculations. A similar problem was considered by Allia and Vinai who adopted a simplified assumption of the domain of an infinitely long cylindrical shape.  相似文献   

19.
Amorphous Fe8585B1515 and Fe8080Cr4.34.3B15.715.7 ribbons were hydrogenated from air side. During spontaneous ribbon dehydrogenation, the hydrogen concentration and the constant of anisotropy induced by internal stress were measured and the ribbon bending, characterized by curvature, was recorded. The results obtained indicate that internal stresses in samples under study are proportional to the hydrogen concentration, and hydrogen distribution is not homogeneous in the cross-section of sample. The hydrogen concentration is the largest in the region close to hydrogenated surface. The hydrogen release from this region is very fast and corresponds to the curvature decrease, and it can be, similar to the decrease of total hydrogen concentration, fitted by exponential function.  相似文献   

20.
The optical properties and the deep levels in bulk Si1−xMnx formed by using an implantation and annealing method were investigated. Transmission electron microscopy, X-ray diffraction, and Hall-effect measurements showed that the annealed bulk Si1−xMnx samples were p-type crystalline semiconductors. The photoluminescence spectra for the annealed bulk Si1−xMnx material showed luminescence peaks corresponding to excitons bound to neutral acceptors and related to dislocations due to the existence of Mn impurities. Deep-level transient spectroscopy results for the annealed bulk Si1−xMnx showed deep levels related to the interstitial and substitutial sites of the Mn+ ions. These results can help improve understanding of the optical properties and the deep levels in annealed bulk Si1−xMnx material.  相似文献   

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