Demagnetization effect of rectangular and ring-shaped samples madeof electrical sheets placed in a stationary magnetic field

The method of summation used for calculating magnetic-field strength is applied to determine the demagnetization coefficient of rectangular and ring-shaped samples made of an anisotropic electrical sheet and of isotropic silicon and silicon-free sheets. The calculations refer to a standard strip used in an Epstein test (of its shortening and contraction) and to the sample which is usually placed in an anisometer, i.e. in a homogeneous external magnetic field. Changes in the demagnetization coefficient are determined for different crystallographic orientation in the above-mentioned sheets. The relation between the magnetization direction of the ring-shaped sample and its demagnetization is affected. In the case of electrical steel strips, the results allow the determination of the real magnetization characteristics for the sample     

Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

Magnetic properties of free ferromagnetic clusters in a Stern-Gerlach magnet

The magnetic properties of free magnetic metal clusters in a Stern-Gerlach magnetic field are studied. In particular we investigate magnetic resonance effects resulting from lattice anisotropy and cluster rotation. The anisotropy field fixed to the rotating atomic lattice of the cluster acts on the cluster magnetization like an RF field in NMR experiments. In our calculation we have used the Bloch equations and assumed different anisotropy field symmetries. A minimum in the magnetization as a function of the Stern-Gerlach field is obtained, if the distribution of the rotation frequency ω_rot is relatively narrow. For other conditions an almost superparamagnetic behavior emerges. In addition, the strength of the anisotropy field and the relaxation time are important quantities which determine the magnetic behavior of the clusters.     

Demagnetization processes and magnetic viscosity of amorphous FeTbfilms

The magnetic viscosity coefficient, S_V, of RF sputtered FeTb films was measured at fields between -5000 and +200 Oe at room temperature. The films, which are amorphous, have a perpendicular anisotropy and a typical stripe domain structure. S_V depends strongly on the demagnetization processes of the films, S _V of the domain-lengthening magnetization process being larger than that of the domain-widening process     

The use of electrical sheets in construction of cryoresistive transformers

The paper discusses the use of electrical sheets with particular emphasis placed on cryogenics transformers. Since the construction of cryoresistive transformers - and not superconducting ones - seems to be more likely, the anisotropy of resistivity and magnetoresistance of the transformer sheets were examined. It is pointed out that both the phenomenon of magnetocrystalline anisotropy and that of anisotropy of resistivity are encountered. Thus, while designing magnetic cores of cryo-resistive transformers it is necessary to consider a much greater range of anisotropy of the sheet core losses than in the case of oil transformers.     

The nuclear refrigeration of copper

Nuclear refrigeration experiments have been performed on samples containing 0.93 g-atom of copper. After demagnetization to a field of 800 G from initial conditions of 25 kG and 16 mK, lattice temperatures of less than 1 mK were reached. The temperature of the copper nuclei was measured with a pulsed nuclear magnetic resonance thermometer. The lattice temperature was then calculated from this value and the experimentally determined heat leak of 0.10±0.02 erg/sec. An attempt to measure the lattice temperature directly by observing the anisotropy in the angular distribution of the rays emitted by 1 µCi of ⁵⁴ MnZN was not successful. A number of solutions of the differential equations describing nuclear refrigeration have been obtained and were used to simulate experiments with various heat leaks and final magnetic fields. Calculations have also been fitted to the experimental results wherever possible.     

Meissner shielding currents and magnetic flux penetration in thin-film superconductors

We have observed the magnetic flux penetration at 4.2 K into superconducting lead films of about 4 µm thickness using a high-resolution magnetooptical technique. The specimens had the shape of small squares or long strips. In increasing magnetic field it was found that magnetic flux starts to penetrate into the bulk of the specimens in the form of flux tubes containing about 60 flux quanta. For the samples with the strip geometry the magnetic fieldH*, at which flux penetration into the bulk sets in, was investigated in the presence of an external electrical currentI along the strip superimposed on the Meissner shielding currents. The fieldH* was found to decrease linearly with increasing transport currentI. The magnetic field near a long superconducting cylinder in the presence of both a transverse applied magnetic field and an applied electrical current parallel to the cylinder axis has been calculated. The calculation is valid for a cylinder of elliptical cross section, which approximates a long, flat strip. The experimental observations for the slope H*/I are in good agreement with the calculations.Work performed in part in the Argonne National Laboratory and in part in the Ames Laboratory of the U.S. Atomic Energy Commission.     

Apparatus for Magnetization and Efficient Demagnetization of Soft Magnetic Materials

This paper describes an electrical circuit that can be used to automatically magnetize and ac-demagnetize moderately soft magnetic materials and with minor modifications could be used to demagnetize harder magnetic materials and magnetic geological samples. The circuit is straightforward to replicate, easy to use, and low in cost. Independent control of the demagnetizing current frequency, amplitude, and duration is available. The paper describes the circuit operation in detail and shows that it can demagnetize a link-shaped specimen of 430FR stainless steel with 100% efficiency. Measurements of the demagnetization efficiency of the specimen with different ac-demagnetization frequencies are interpreted using eddy-current theory. The experimental results agree closely with the theoretical predictions.      

P型半导体金刚石膜的磁阻

研究了p-型异质外延和同质金刚石膜的在不同温度和磁场下的磁阻,磁阻器件的结构为条形和圆盘形,实验结果表明磁阻强烈依赖于磁场、温度和样品的几何形状,圆盘结构的磁阻大于条形结构,条形结构的磁阻还取决于不同的长-宽比。利用F-S薄膜理论,计算磁场为5T时条形和圆盘结构的磁阻分别为0.38和0.74,讨论了霍耳效应对磁阻的影响。给出了形状效应的可能机制。     

Templates as Shadow Masks to Tune the Magnetic Anisotropy in Nanostructured CoCrPt/Ti Bilayer Films

Off‐axis deposition of Ti and CoCrPt films onto lithographically patterned templates has been used to make nanostructures with a lateral thickness variation that allows the tuning of the magnetic anisotropy. CoCrPt rectangles of 1 μm × 725 nm without a thickness variation show an out‐of‐plane easy axis and a single‐domain configuration after demagnetization. On the other hand, rectangles with a thickness variation along their longer dimension show an out‐of‐plane multidomain state, but an in‐plane vortex configuration occurs when the thickness variation is along the shorter dimension. The evolution of the magnetic behavior is understood from the change in both Ti and CoCrPt thicknesses and their effects on the magnetic anisotropy, and provides a simple method for controlling the magnetic state and reversal process of patterned nanostructures.     

Physical Processes Near and on a Twin Boundary in High-Temperature Superconductors and an Oscillatory Differential Method for Investigating These Processes

An oscillatory differential method is developed for local diagnostics of superconductors with a view to obtaining useful information simultaneously on the physical processes that occur near and on a twin boundary and on the period of twin boundaries. In the magnetic-field dependence of the trapped magnetic flux and of the effective demagnetization factor of YBCO samples in the form of a thin disk, regular steps are observed over certain intervals of the external field. These results are attributed to the decomposition of a sample into twin domains as the external magnetic field increases and allow one to determine the transversal size of the domains.     

Surface coating of carbon nanofibers/nanotubes by electrodeposition for multifunctionalization

Carbon nanomaterials in the form of paper sheets have been used as platforms to achieve multifunctionality. Combined with electrochemical deposition, room temperature synthesis of magnetic Ni coatings on individual carbon nanofibers (CNF) and/or carbon nanotubes (CNT) has been realized through solution penetration and ion diffusion. In addition to significant electrical conductivity improvement, the magnetic responses of the Ni coated carbon nanopaper sheets can be tuned within large ranges in terms of saturation magnetic field, remnant magnetization and coercivity. After being re-suspended in liquids, the magnetized CNFs/CNTs can be aligned with small external magnetic fields.     

Calculation of exact head and image fields of recording heads byconformal mapping

An exact conformal mapping calculation is carried out, which maps the entire upper edge of an idealized ring head and a symmetric thin-film head in the complex z plane to the real axis of the complex t plane, and uses the slotted-plane approximation to obtain the inverse mapping function t(z). The latter is used to calculate not only the head fields of a given geometry, but also the kernal function to evaluate the total demagnetization field of the interaction head-media system including the media self-demagnetization and the image field induced on the head poles. The total demagnetization field contours for a single-bit arctangent transition and a dibit biquadratic transition corresponding to various head configurations have been obtained and their physical meaning elaborated on     

Magneto-optical properties of obliquely evaporated Ni films

Longitudinal magneto-optical Kerr effect (MOKE) configuration and scanning electron microscopy (SEM) were used to investigate the effects of deposition angle, on magnetic properties and morphology of obliquely evaporated Ni films. The results show that the angle of deposition has a critical effect on the magnetic anisotropy of the films. These effects are due to the microstructure of the films, which is controlled by the angle of deposition with respect to the sample normal. The results show the presence of shape anisotropy governing the demagnetization of the magnetic fields. The anisotropy, coercivity and squareness of the hysteresis loops increased with an increase in of the vapour flux. These properties and surface roughness became marked for off-normal deposition angles larger than 50°. At low s, the easy axis of magnetization lay perpendicular to the incidence plane. At large s the easy axis changed parallel to the incidence plane. The results may be quantitatively understood from the presence of an inclined columnar microstructure with shape anisotropy governing the demagnetization of the magnetic fields.     

Faster magnetic walls in rough wires

In some magnetic devices that have been proposed, the information is transmitted along a magnetic wire of submicrometre width by domain wall (DW) motion. The speed of the device is obviously linked to the DW velocity, and measured values up to 1 km x s(-1) have been reported in moderate fields. Although such velocities were already reached in orthoferrite crystal films with a high anisotropy, the surprise came from their observation in the low-anisotropy permalloy. We have studied, by numerical simulation, the DW propagation in such samples, and observed a very counter-intuitive behaviour. For perfect samples (no edge roughness), the calculated velocity increased with field up to a threshold, beyond which it abruptly decreased--a well-known phenomenon. However, for rough strip edges, the velocity breakdown was found to be suppressed. We explain this phenomenon, and propose that roughness should rather be engineered than avoided when fabricating nanostructures for DW propagation.     

Effect of antimony surface treatment on nitrogen absorption during batch annealing of an electrical steel sheet

Nitrogen absorption is usually observed during batch-type hot-band annealing of electrical steel sheets containing aluminium. This nitrogenizing causes the deterioration of magnetic properties, such as core loss and induction. In order to prevent nitrogenizing, we investigate an antimony treatment on the hot strip surface of electrical steel sheets containing aluminium. Potassium antimonyl tartrate and colloidal antimony oxides (Sb2O5) are effective against nitrogenizing. It seems that active sites on the surface of the hot strip after pickling are covered with antimony oxides to block the adsorption of nitrogen. Magnetic properties, after cold-rolling and continuous annealing of the nitrogenizing hot band, deteriorate due to small grains near the surface whose boundaries are pinned by aluminium nitrides.     

NiTi substituted hexaferrites for magnetic recording

In order to obtain hexagonal ferrites with improved characteristics for application in the field of the magnetic recording, the ferrimagnetic Sr(NiTi)_x Fe_12-2xO₁₉ system is studied. Preliminary investigations suggested that NI is more effective than Co in reducing the magnetic anisotropy of hexaferrites. The system was analyzed as a function of the degree of substitution x and of the reaction temperature T_R and time τ. The reactivity of the mixtures and their magnetic characteristics (σ, H_c, H_A, T_c) were measured, and from the _χT(H) data it was possible to distinguish between single-domain or polydomain particles. The results are presented. The influence of the extraneous magnetic phases on the coercive field value was also studied and a preliminary investigation of the relation between coercive and anisotropy fields was carried out     

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T_s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T_s results in an increase of both the bulk saturation magnetization M_s and the perpendicular coercivity H_c^⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T_s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M _s, or in geometric structure, resulting in different values of the demagnetizing factor N_d, are the most probable causes of the observed effects     

The anisotrophy of coercive force in cold-rolled goss-texture electrical sheets

The value of coercive force constitutes an important materals constant, and an unfavorable effect of Hcchanges should be taken into consideration in the course of exploitation of electrical machines and equipment. The values of coercive force of anisotropic and isotropic electrical sheets have been presented. It has been found that the crystalline structure and the degree of texture bring forth the anisotropy of coercive force, i.e., the changes of Hcvalue depending on the magnetization directions. The applied measuring method gives results which are exact enough (error δmax< 3 percent) and reproducible. The minimal value of coercive force has been found to be in direction [001] and the maximal value in direction [110], and not in direction [111]. The anisotropy for the directions is correlated with the anisotropy of mechanical properties (the number of bends) and the magnetostriction.