摘要:

Using long Josephson tunnel junctions, dynamic vortex motion has been observed as the flux‐flow voltage across the junction. The flux‐flow voltage increases with increasing external magnetic field. The velocities of the flux flow in the junctions can be obtained from the junction‐voltage–vs–applied magnetic field characteristics. It is shown that the velocities of the flux flow in the long junctions have the maximum value equal to the phase velocity of the electromagnetic field.

ISSN:0021-8979    

DOI:10.1063/1.325521

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The dispersion relation of magnetostatic surface waves propagating in a ferromagnetic film of finite dimensions is derived. Specifically, a consideration of the finite width of the sample is introduced to the previous treatments of magnetostatic surface‐wave propagation. The inclusion of a finite width produces a multiplicity of propagating modes, which can be excited individually or collectively, depending on experimental conditions. In addition, the finite width allows the excitation of magnetostatic volume waves, which exist over a narrow frequency range just below the range of magnetostatic surface waves. All aspects of the theoretical analysis are supported by measurements made on magnetostatic surface‐wave propagation at frequencies around 1 and 9 GHz in yttrium iron garnet samples of different widths.

ISSN:0021-8979    

DOI:10.1063/1.325522

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A generalized form of mean field theory and procedures for applying it to analyze experimental data on the temperature dependence of the saturation magnetization or the effective gyromagnetic factor ofn‐component amorphous transition‐metal–rare‐earth alloys are outlined. This analysis yields the spin values of each component and the effective exchange interaction energies between them, from which other magnetic properties such as the subnetwork magnetizations and the macroscopic exchange stiffness can be calculated. Examples of application of this mean field procedure are given.

ISSN:0021-8979    

DOI:10.1063/1.325523

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Permeability‐temperature curves of polycrystalline Mn0.41Zn0.42Fe2.16O4+xare interpreted in terms of theoretical models using the intrinsic magnetic properties as measured on a single crystal having virtually the same composition. The temperature dependence of &mgr; can be fitted by the relation &mgr;∼M/K1/2, as expected for cylindrical wall bulging, but the absolute value of &mgr; is an order of magnitude below the theoretical value. Spherical bulging of a totally pinned wall is shown to yield a &mgr; which is an order of magnitude smaller than the observed value due to the stiffness of the wall due to demagnetizing and anisotropy energy. It is suggested that a finite pinning of the walls at the grain boundary might explain our data. After annealing at pressures near the phase boundary, the theory does not fit the &mgr;‐Tcurves. It is suggested that the bulk composition of the grains of the polycrystalline material is different from that of the single crystal due to preferential segregation at the grain boundary even before a second phase is formed.

ISSN:0021-8979    

DOI:10.1063/1.325524

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The magnetic and structural properties of GdFe2thin films prepared by electron beam coevaporation have been investigated. The measurements included magnetic resonance, magnetometer, the Mo¨ssbauer effect, x‐ray diffraction, and Auger analysis. Comparisons were made between the properties of the as‐deposited amorphous films and films annealed at various temperatures up to 500 °C, at which point crystallization is essentially complete. The measured magnetization for amorphous films was less than the magnetization measured in crystalline films at all temperatures. The magnetic moment of the Gd and Fe ions within their respective magnetic sublattices were determined to be 7.6 and 2.12&mgr;&bgr;for crystalline GdFe2. The sublattice moments in the amorphous case do not change appreciably from the crystalline case. The sublatticegvalues were determined to be slightly temperature dependent below 77 K. The Landau‐Lifshitz magnetic damping parameter was determined to be ∼1×107and 2×107Hz for amorphous and crystalline films, respectively. For amorphous thin films on a Si substrate overcoated with Si, the spin‐wave mode field positions obeyed an2law withA/M=1.2×10−9Oe cm2, in agreement with calculation.

ISSN:0021-8979    

DOI:10.1063/1.325525

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In order to determine the relative contribution of primary pyroelectricity and secondary pyroelectricity to the total pyroelectric coefficient of polyvinylidene fluoride, samples have been heated suddenly using a 200‐ps laser pulse and the time dependence of the appearance of the pyroelectric charge measured. Charge resulting from primary pyroelectricity would appear as fast as the sample is heated, but charge resulting from secondary pyroelectricity would appear only as rapidly as the sample can relax to the new higher‐temperature dimensions. The results indicate that no significant fraction of the pyroelectricity of polyvinylidene fluoride is primary pyroelectricity. It is suggested that a reversible temperature dependence of the crystallinity might provide an important contribution to pyroelectricity.

ISSN:0021-8979    

DOI:10.1063/1.325526

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The response of a lead zirconate titanate ceramic to statically applied uniaxial stresses in the range 0–0.4 GPa has been investigated. The material studied was a niobium‐doped composition with the chemical formula Pb0.99Nb0.02(Zr0.95Ti0.05)0.98O3. Properties measured as a function of stress include electrical charge release from poled specimens, ferroelectric hysteresis‐loop behavior, macroscopic strains, and ultrasonic velocities. Data from the experiments exhibit anomalous behavior at low‐stress levels (0.05–0.2 GPa). Comparison with similar data obtained under conditions of hydrostatic pressure indicate that the anomalies observed in the uniaxial‐stress experiments are caused by domain‐reorientation processes rather than by the ferroelectric to antiferroelectric phase transition. This transition occurs at 0.32 GPa under hydrostatic‐pressure conditions, but no evidence for it is seen in the uniaxial‐stress measurements to 0.4 GPa. The relationship of the present results to other uniaxial‐stress studies and to shock‐wave studies on ferroelectric ceramics is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325527

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The measurement of the response of Mg2SiO4 : Tb thermoluminescent dosimeter against radiation dose has been made and the result is presented. The supralinearity observed is characterized by (1) a clear power‐law relation between the response and the dose and (2) a sharp transition from the linear to the supralinear region, a behavior which has not been found in other phosphors. A few existing models are shown to be insufficient to explain the above features. A new model seems to be appropriate.

ISSN:0021-8979    

DOI:10.1063/1.325528

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The thermionic emission of positive alkali ions from zeolites has been investigated in the high‐voltage pulsed regime. Current densities of up to 1 A cm−2have been obtained using 2‐&mgr;s‐long 30‐kV pulses. This is about two orders of magnitude larger than currents obtained in the low‐voltage dc regime. There are two major reasons for this difference. First, the currents have a Schottky‐type dependence on electric field, and second, the current rapidly decays in dc operation. The desorbed ion fluxes are up to a million times larger than those for neutrals for high‐voltage pulses. The ratio of these two fluxes can be described by the Saha‐Langmuir equation. This indicates that the alkali atoms and ions are in thermal equilibrium at the surface of the zeolite.

ISSN:0021-8979    

DOI:10.1063/1.325529

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is shown that in thermocouples consisting of arms in the form of coaxialNandPdisks in which the current flow is radial, two regions must be distinguished. If theNandPdisks are narrowly spaced, then the temperature difference between the hot and cold junctions tends to infinity. If, on the other hand, the disks are widely spaced, then the maximum temperature difference is the same as that of a linear couple.

ISSN:0021-8979    

DOI:10.1063/1.325530

出版商:AIP    

年代:1978

数据来源: AIP