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1.
Several aspects of the Barkhausen effect can be investigated by using a measurement equipment that records the Barkhausen signal as a function of time in digital form on computer tape. Measurements on thin magnetic films containing a small number of domain walls are presented. The behaviour of the wall jumps during a reversal is investigated. During the steep part of the loop the stationarity of the signal is measured with the magnetic field as a parameter. The influence of the coercive fieldH c and the thicknessd m is considered and compared with results obtained by others on bulk samples.  相似文献   

2.
Magnetic and superconducting properties of Fe/Nb epitaxial bilayers have been studied. Single crystal Fe/Nb (110) bilayers with a Nb thicknessd Nb in the range from 250 to 650 Å and with a Fe thicknessd Fe in the range from 7 to 27 Å were prepared using molecular beam epitaxy techniques. Magnetization measurements showed the existence of a magnetically “dead” Fe-interface layer with a thicknessd NM varying strongly with minor modifications of the growth conditions. For bilayers with a small magnetic layer thicknessd M and a smalld NM the FMR measurements revealed an anomalous decrease of the effective magnetization 4πM eff of the ferromagnetic Fe layer below the superconducting transition temperatureT c. The absolute change of 4πM eff belowT c depends strongly on the actual values ofd M andd NM: upon decreasing bothd M andd NM the effect increases considerably. As a possible mechanism for the anomalous temperature dependence of 4πM eff belowT c we discuss a spatial modulation of ferromagnetic order due to a modification of the RKKY inter-action in the superconducting state.  相似文献   

3.
The eletrical conductivity of antimony films of different thicknesses was studied at different temperatures. For small thicknessd, whereL is the electron mean-free path, the film resistances varies asd ?n , wheren=2. However, ford?L the value ofn becomes smaller than 2 which is in agreement with the theory.  相似文献   

4.
A calculation of the bound states in a paramagnetic-superconducting contact, valid at any temperature belowT c, is performed by using a recently developed method of solving the Bogoliubov equations. The problem of self-consistency of the pair-potentialΔ(x) is being avoided by leaving open the detailed form ofΔ(z), introducing instead the characteristic lenghth for the spatial variation of the pair-potential,d=O D (1?Δ(z)/Δ)dz, as a fit parameter. The energies, the quasiparticle wave-functions and the density of the bound states are calculated for negligible impurity scattering. The energy gap of the excitation spectrum reduces from about one third of its bulk value to practically zero as the thicknessa of the normal film increases froma?d toa?d.  相似文献   

5.
The Curie temperature Tc of a proximity sample composed of a thin film of a weak itinerant ferromagnet of thickness df in contact with a thick film of an enhanced parmagnetic metal is calculated using the Hubbard model in the Hartree-Fock approximation. The sample is paramagnetic for values of df less than a critical thickness df0 of the order of the coherence length. The shape of the curve of Tc vs. df for df > df0 depends on whether the bulk ferromagnet exhibits a Curie-Weiss or a Pauli susceptibility above the bulk Curie temperature. The letter is concluded by comments on the experimental situation.  相似文献   

6.
Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = Bs ? Bm exp ? f/fc where Bs, Bm and fc are constants. This equation indicates that B approaches a saturation value Bs when f?fc and a linear relation between B and f when f?fc. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V12)] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.  相似文献   

7.
A Monte Carlo simulation of the 1/f noise spectra in the normal phase of YBa2Cu3O7 epitaxial films is reported. It is conjectured that the main contribution to the noise is from oxygen transitions to vacant sites in the CuO plane. It is shown that the annealing regime and the mismatch strains between the film and the substrate are the main factors governing the domain and defect structure of the film and, hence, the 1/f noise spectrum. Fiz. Tverd. Tela (St. Petersburg) 41, 957–964 (June 1999)  相似文献   

8.
The structure and energy of asymmetric vortex-like Bloch and Néel walls in a magnetically uniaxial film with an easy magnetization axis lying in the film plane are investigated by numerically minimizing the total energy within the rigorous micromagnetic approach and the two-dimensional model of the magnetization distribution. The calculations are performed over wide ranges of film thicknesses b (up to b = 1 μm) and magnetic parameters of the films. It is established that the asymmetric vortex-like domain walls are the most universal wall structures in the films under consideration. In magnetically uniaxial films, unlike in magnetically multiaxial films, the asymmetric Bloch walls are always stable.  相似文献   

9.
A sinusoidal ac current of frequeencyf c generates an excess noise in many solidstate conductors. The power spectrum of this noise is calculated starting from the autocorrelation function of the stochastic process. Besides a 1/Δf term the spectrum includes another contribution varying with 1/(f c+f). In the low frequency range there is white noise.  相似文献   

10.
The orientation dependences of the converse longitudinal piezoelectric constant d33,f, and the in-plane converse piezoelectric constant e31,f, are calculated for tetragonal barium titanate epitaxial films. The calculations demonstrate that both e31,f and d33,f have their maximum values along an axis close to the (1 1 1) direction of the pseudo-cubic system, which are similar to the orientation dependence results for a tetragonal BaTiO3 single crystal. The calculated piezoelectric constants for a (1 1 1) oriented BaTiO3 epitaxial film (e31,f = −23 C/m2, d33,f = 124 pm/V) suggest that it is a good candidate material for lead-free MEMS applications.  相似文献   

11.
The crystallization of vacuum-deposited amorphous Dy-Fe thin films was studied by transmission electron microscopy and electron diffraction. The effect of thickness, deposition rate and substrate temperature on the crystallization process have been investigated. The results show that the crystallization thicknessd c decreases with increasing deposition rate and substrate temperature. The number density of Dy-Fe islands were found to be almost constant at (4–5)×1011 cm–2 in the thickness range 20 Å<d <50 Å. The number density decreases with increase ind c .  相似文献   

12.
Molybdenum films are obtained by quenched condensation of the metal vapour onto a He-cooled substrate. During annealing the electrical resistance decreases over a small temperature range; this is the typical behaviour of amorphous metals. The films, about 300 Å thick and with a high resistivity, have a positive Hall effect. The transition temperature Tc = 8.0 K is strongly enhanced compared to crystalline Mo. The upper critical field strongly enhanced compared to crystalline Mo. The upper critical field Bc2(T) has been measured. In the examined field range up to 80 kG, Bc2 is a linear function of temperature; the slope has the large value dBc2/dT = -45 kG/K.  相似文献   

13.
Although during the last years one has seen a number of systematic studies of the surface energies of metals, the aim and the scientific meaning of this research is to establish a simple and a straightforward theoretical model to calculate accurately the mechanical and the thermodynamic properties of metal surfaces due to their important application in materials processes and in the understanding of a wide range of surface phenomena. Through extensive theoretical calculations of the surface tension of most of the liquid metals, we found that the fraction of broken bonds in liquid metals (f) is constant which is equal to 0.287. Using our estimated f value, the surface tension (γm), surface energy (γSV), surface excess entropy (−dγ/dT), surface excess enthalpy (Hs), coefficient of thermal expansion (αm and αb), sound velocity (cm) and its temperature coefficient (−dc/dT) have been calculated for more than sixty metals. The results of the calculated quantities agree well with available experimental data.  相似文献   

14.
The spectrum of standing spin waves has been detected by the ferromagnetic resonance method in NiFe(740 Å)/Cu/NiFe(740 Å) three-layered film structure in the perpendicular configuration for the copper thickness d Cu ≤ 30 Å. At thicknesses d Cu > 30 Å, the resonance absorption curve is a superposition of two spinwave resonance spectra from individual ferromagnetic NiFe layers. For Co/Pd multilayer films, united spinwave responance spectra have also been observed at thicknesses of the paramagnetic palladium layer up to d Pd < 30 Å. The partial exchange stiffness has been calculated for a spin wave propagating across the Pd layer (A Pd = 0.1 × 10?6 erg/cm). This value is always positive (up to the critical thickness of the palladium interlayer d Pd < d c) or equal to zero (d Pd > d c).  相似文献   

15.
《Physics letters. A》1997,235(5):504-507
The m = 1 diocotron mode frequency fd of spheroidal electron plasmas formed in a train of many ring electrodes has been found to approach the value for a cylindrical plasma in a conducting wall as the aspect ratio α increased. For small α and total charge, fd became closer to the (ℓ = 1, m = 1) the mode frequency for the case of a free boundary.  相似文献   

16.
A spectroscopic prism coupler is created for measuring refractive indices nf and thicknesses Hf of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of nf and Hf are performed using measured angular positions θm of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θm, we can calculate effective refractive indices βm of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index nf and thickness Hf of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.  相似文献   

17.
The Barkhausen jumps occuring during the magnetization of the amorphous Fe-Ni-B-Si alloys have been studied by the measurements of the derivative of magnetization with respect to time (dM/dt). The peaks in dM/dt vs. applied field (H) are reproducible after averaging over some fifty cycles of magnetization. The investigation of the variations of dM/dt with the applied field (H) and with the instantaneous magnetization (M) accompanied with the same studies, but performed starting from different values of the initial remanence (Mri), completes our earlier analysis of the process of magnetization in these alloys. It is shown that the model of Chikazumi used for the explanation of the variations of remanent magnetization, coercive field and loss with the maximum magnetization (Mm) is consistent with the observed Barkhausen jumps. The possibility of separation of contributions from particular domain walls to the process of magnetization in soft magnetic materials (which would enable the determination of the locations and strengths of the particular pinning centres) is briefly discussed.  相似文献   

18.
Structural and superconducting properties of the system Lu1?x Ca x Ba2 Cu3O7?δ, both in bulk as well as thin film form, have been investigated. Presence of large Ca-ions at the Lu-sites is responsible for phase stability (in 1–2–3 phase) in bulk. In argon annealed tetragonal samples (δ:1) superconductivity is reinstated as in these samples, presence of Ca-ions lead to the generation of holes in the Cu?O planes. In oxygen annealed bulk samples and thin films, there is a large depression ofT c due to divalent Ca-ions present in concentrationx<0.2. Our data indicate that this depression ofT c is likely due to overdoping effect.  相似文献   

19.
We have carried out X-ray absorption measurements with its magnetic circular dichroism (MCD) of perpendicular magnetic films of DyxCo100−x (15?x?33) at Dy M4,5 and Co L2,3 absorption edges to investigate electronic and spin states of the Dy 4f and Co 3d states, respectively. The replacement of major spin between Dy 4f and Co3d is clearly observed in the spectra between 20?x?25. The expected values of the orbital angular moment ∣〈Lz〉∣ of Dy 4f were estimated to be 1.4-0.8 μB while that of Co 3d was estimated to be around 0.2 μB.  相似文献   

20.
The domain wall motion in the presence of an in-plane magnetic field Hy perpendicular to the wall is simulated using a fall implicit numerical scheme. Calculations are performed for the drive fields 0 Oe<Hz<15 Oe and in-plane fields -210 Oe?Hy?210 Oe. The relation between the average wall velocity v and the drive field Hz is discussed considering the wall structure. It was found that an in-plane field increases the peak velocity of the wall and extends the range of the drive fields, where the linear mobility relation is valid. A dynamical Bloch line stacking was found for sufficiently large drives. The influence of an in-plane field on the angular span of horizontal Bloch lines is discussed also. In particular the occurrence of 2π-horizontal Bloch lines is described. Numerical results obtained with a full implicit method are compared with the experimental observations of bubble motion and good agreement is found for |Hy|≤100 Oe.  相似文献   

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