首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 718 毫秒
1.
Magnetic anisotropies were investigated for CoCr perpendicular magnetic films on grooved structure substrates (pitch length 2.1 μm) prepared by CF4-reactive-ion etching. Perpendicular magnetic anisotropy decreases in the region where groove depth GD >650 A. The reduction is due to the inclination of the crystal growth axis on the groove surface. In-plane magnetic anisotropy, Ku∥, strongly depends on GD and saturation magnetization Ms. In a region of large GD and large Ms, Ku is mainly due to shape anisotropy. In a region of small GD and small Ms , Ku∥ is caused by perpendicular magnetic anisotropy, in addition to shape and magnetorestrictive anisotropy  相似文献   

2.
CoNiTa/Cr double-layered films for longitudinal magnetic recording media have been prepared by using the facing targets sputtering apparatus. Substrate heating and postannealing were performed in order to increase the coercive force Hc. While the as-deposited film at the substrate temperature Ts of 400°C had Hc of 780 Oe, the films deposited at Ts of room temperature, exposed to atmosphere, and annealed at 400°C, had Hc as high as 1700 Oe. It has been found that the same amount of Cr atoms migrated from the underlayer to the magnetic layer and the vicinity of the film surface. Consequently, such a large increase of Hc seemed to be caused by isolation of magnetic grains by Cr atoms in their boundaries  相似文献   

3.
In order to identify a hard magnetic phase in rapidly quenched Zr-Co-B alloys and clarify its magnetic properties, Zr-Co-B ribbons, Zr-Co ribbons, and Zr-Co ingots were studied. The hard magnetic phase is interpreted as a Zr2Co11 intermetallic compound. This compound has a Curie temperature of 500°C and uniaxial magnetic anisotropy with an anisotropy field of 34 kOe. The magnetization of this compound was estimated to be 67 emu/g at 15 kOe. In addition to the hard magnetic phase, the low and high Tc phases appear in both binary and ternary alloys. The low Tc phase is FCC Zr6Co23 with Tc=180°C. The magnetization of Zr6Co23 was estimated to be 44 emu/g at 15 kOe. The high Tc phase is cobalt including a small amount of zirconium. In Zr-Co-B alloys, suitable boron addition is shown to enhance the coercive force. On the other hand, the addition increases the magnetization. While the boron addition produces cobalt, it reduces Zr6Co23 or quenches its ferromagnetism  相似文献   

4.
In order to obtain hexagonal ferrites with improved characteristics for application in the field of the magnetic recording, the ferrimagnetic Sr(NiTi)x Fe12-2xO19 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 TR and time τ. The reactivity of the mixtures and their magnetic characteristics (σ, Hc, HA, Tc) 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  相似文献   

5.
Fine ceramic powders of Sr0.9Ca0.1Zn2 Fe16O27 (Sr0.9Ca0.1Zn 2-W) ferrite, of almost single domain grain size ~1 μm, have been synthesized successfully by sintering for a few hours a mixture of SrCO3, CaCO3, ZnO, and α-Fe2 O3 in stoichiometric amounts at an effectively low temperature (Ts) of ~1100°C. Carbon dioxide evolves in the reaction Sr(Ca)CO3+2ZnO+8 α-Fe2D3 &lrarr2;Sr(Ca)Zn2Fe16O2+C2 , making fine pores in the sample, which prevent large grain growth of the material and result in a very loose powder. The small ⩽10% substitution of Sr by Ca activates the reaction, but preserves the crystallization of the small-sized grains. This yields magnetic properties useful for most permanent magnet applications, with a promisingly high coercivity Hc~3650 Oe and saturation magnetization Ms~65 emu/g. A considerably better saturation magnetization Ms~85 emu/g can be obtained by sintering the samples at higher Ts~1300°C, but that results in a rather very low coercivity Hc~105 Oe  相似文献   

6.
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, Hk(t), is well represented by the following formula: ln {1-Hk(t )/Hk(∞)∝-√Tt, where Hk(∞) 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  相似文献   

7.
A finite element formulation of current-driven eddy current problems in terms of a current vector potential and a magnetic scalar potential is developed. Since the traditional T-Ω method enforces zero net current in conductors, an impressed current vector potential T0 is introduced in both conducting and nonconducting regions, describing an arbitrary current distribution with the prescribed net current in each conductor. The function T 0 is represented by edge elements, while nodal elements are used to approximate the current vector potential and the magnetic scalar potential. The tangential component of T is set to zero on the conductor-nonconductor interfaces. The method is validated by computing the solution to an axisymmetric problem. Problems involving a coil with several turns wound around an iron core are solved  相似文献   

8.
In high fields where the magnetization is approaching saturation, the resolved magnetic polarization I can be expressed by a power series of the inverse of external field H as: I=Is-b/H 2-c/H3 . . ., or alternatively in terms of the reversible permeability μrev=1+(2b/H3+3c/H4+ . . .)/μ0 where Is is the spontaneous magnetic polarization and b, c, are constants. These equations express the law of approach to saturation magnetization. The coefficient b for a cubic crystal has been deduced as b=0.0762/Is[K+1.5(λ100111)σ]2, where σ is the applied stress and others are magnetic constants. The values of reversible permeability μrev under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress, The values of magnetic constant K andλ100111 were calculated, They agreed with the standard values, but were affected by chemical composition and heat treatment of materials, especially in λ100111  相似文献   

9.
An automatic technique for measuring the parameters of Polder resonance in polycrystalline ferrite spheres is proposed. The diagonal elements of the external susceptibility tensor versus DC magnetic field are calculated from the changes in resonance frequency and unloaded Q factor of a microwave cavity by perturbation theory. From these diagonal elements, all the elements of the intrinsic permeability tensor can be obtained. By fitting the theoretical curves to experimental data, the parameters of Polder resonance, ΔH Ms, and the g factor, are simultaneously calculated. The whole measurement procedure is controlled by a desktop computer. An accuracy of 5% is obtained in ΔH and M s, and of 0.1% in the g factor  相似文献   

10.
Magnetic properties for sputtered CoCrTa films (18 at.% Cr and 2.0-3.0 at.% Ta), which were deposited under various background pressures Pi, and argon sputtering pressures, P Ar, have been examined. The perpendicular anisotropy field Hk for CoCrTa films maintains high values of 5-6 kOe in a wide range of Pi and PAr , as compared with that for CoCr films. In order to optimize Ta composition, magnetic properties and crystalline microstructures for Ta additive content (0-4.0 at.%) have been investigated. Hk and perpendicular coercivity Hc⊥ increase with increasing Ta concentration above 2.0 at.% Ta. C-axis orientation is improved by adding Ta to CoCr films. However, above 3.0 at.% Ta, Hc⊥ steeply decreases and domain wall motion is observed, owing to the increase in crystalline grain size. The appropriate Ta composition is 2.0-3.0 at.%  相似文献   

11.
The temperature dependence of magnetization in Sm3Fe 20Cx (x =0.3, 0.6, 0.8) and Sm2Fe16.5C1.0 intermetallic compounds with rhombohedral structure has been analyzed using molecular field theory. On the basis of a two-sublattice model, the molecular field coefficients are calculated using a numerical fitting method. The Curie temperature and the Fe-Fe, Sm-Fe, Sm-Sm magnetic interaction energies for the compounds are determined from these coefficients. The results show that the increase of the Curie temperature (Tc) with the increase of carbon content x is attributed mainly to the enhancement of the Fe-Fe exchange interaction energy caused by carbon atoms added  相似文献   

12.
The magnetic viscosity coefficient, SV, 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. SV 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  相似文献   

13.
Modified electron spin resonance (ESR) techniques were used to measure low-field (<200 Oe) microwave absorption of high-T c cuprates YBa2Cu3O7-x. A series of experiments on polycrystalline and single-crystal samples in which the angle between the DC and the modulating magnetic fields was varied showed that the microwave absorption obeys results predicted from thermodynamic considerations of fluxoids. The absorption takes place in the normal regions created by flux penetration at low fields in these samples. The change in magnetically modulated microwave absorption on passing through Tc is explained by the decrease in absorption that occurs when part of the sample becomes superconducting and by the rapid variation of the penetration depth near Tc. The technique is an extremely sensitive method of detecting superconductivity in very small samples and for studying the superconducting state. Possible applications such as microwave attenuators, magnetic memories, and gaussmeters are discussed  相似文献   

14.
W-type Pb-hexaferrites were prepared by standard ceramic methods. The lattice constants found by refinement were a=0.59140±0.00006 nm and c=3.29209±0.00041 nm. The X-ray density of a typical composition PbZn1.9Fe15.3O25.8 was ρ=5.32 g/cm3 and the Vickers microhardness value h v=6 kN/mm2. A plot of the saturation magnetization versus temperature is given. The extrapolated value of the saturation magnetization (H→∞, T→0) was σs=108 emu×g-1, and the Curie temperature was Tc=600±20 K  相似文献   

15.
The proton gyromagnetic ratio in H2O is measured by the low-field method. γ'p(low)=2.67513376×108 s-1 T-1 (0.11 p.p.m.), leads to a value of the fine structure constant of α-1=137.0359840 (0.037 ppm) and a value for the quantized Hall resistance in SI units of RH=25812.80460 Ω (0.037 p.p.m.). To achieve this result, the dimensions of a 2.1-m solenoid were measured with an accuracy of 0.04 μm, and the NMR (nuclear magnetic resonance) frequency of a water sample was measured in the field of the solenoid  相似文献   

16.
The authors used a DC SQUID (superconducting quantum interference device) to measure the low-frequency magnetic flux noise produced by thin-film rings of YBa2Cu3O7-δ (YBCO) with various microstructures. Below the transition temperature T c of the YBCO, the spectral density of the noise scales as 1/f (f is the frequency) from 1 Hz to 1 kHz. This noise generally increases with temperature and vanishes abruptly at Tc . Improvements in crystalline microstructure greatly reduce the magnitude of the noise, which was lowest for a highly orientated sample with its c-axis perpendicular to the substrate. Making a radial cut to interrupt current paths around the sample ring does not significantly affect the magnitude of the noise, demonstrating that the noise arises from a local mechanism such as the thermally activated hopping of flux bundles. Flux creep was observed in one sample cooled in a magnetic field of 1 mT, and the creep rate exhibited a sharp maximum near 80 K. It is concluded that SQUIDs and flux transformers of YBCO must be fabricated from highly orientated films to obtain low noise at low frequencies  相似文献   

17.
A measurement channel which consists of a multiplexer, sample-and-hold circuit, and analog-to-digital (A/D) converter is studied. It is designed for the synchronous sampling and measurement of two or more voltage signals V1(t), V 2(t), . . ., but the finite time of A/D conversion (ΔT) makes it impossible to acquire consecutive samples closer in time than ΔT. This can become a source of measurement error if further processing of the measurement data is based on the assumption of ideal synchronism. It has been found that interpolation filters, developed from the Lagrange polynomial interpolation, are useful tools for solving the problem of correction. An illustrative example of their use is presented  相似文献   

18.
Remarkable nonlinear inductances due to the soft magnetic BH hysteresis characteristics are obtained for YBa2Cu3O7-x disk-shaped cores at 77 K which are tightly wound with polyester-coated copper coils. The inductance changes from nearly zero due to the Meissner effect to that of an equivalent coreless coil as a result of the flux penetration effect due to increasing the exciting current or the applied external magnetic field. Values of inductances are almost constant from low frequency to at least 20 MHz, indicating that the high-Tc superconductor is a fast-response nonlinear inductor material. Fast-response magnetic modulators use one toroidal core or one pair of disk cores with a carrier frequency of more than 10 MHz and a signal frequency of 0 to 500 kHz  相似文献   

19.
L.S. Czarnecki's (1985, 1987, 1988) orthogonal decomposition of nonsinusoidal currents is briefly discussed. The minimum property of Czarnecki's active currents in single-phase and three-phase nonsinusoidal circuits is discussed, using a Lagrangian multiplier approach. Czarnecki divided current, i, into three components: the active current ia, the scattered current i s, and the reactive current ir. For three-phase four-line systems, several meanings of Czarnecki's active current ia are given  相似文献   

20.
(Tb20Fe65Co15)94Cr 6 film shows high corrosion resistance with good magnetooptical properties, Hc=4.9 kOe, &thetas;k=0.3°, Ku=1.4×106 erg/cm3 and Tc=230°C. Pit corrosion in 1N-NaCl aqueous solution and wet corrosion in 85°C and 85%RH atmosphere were studied for TbFeCo films with and without Cr addition. It is suggested that pit corrosion occurs by a chemical reaction between the anodic pit wall and the cathodic film surface, resulting in a piling up of corroded products inside the pits. On the other hand, wet corrosion in TbFeCo and TbFeCoCr films shows a bubble-chain-like morphology similar to conventional filiform corrosion observed in a coated film. This seems to take place by discontinuous movement of the anodic reaction area ahead of the bubbles  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号