摘要:

An expression is derived for noise in the tank circuit of a superconducting quantum flux detector run at a radiofrequency. This noise is limited by the sensing element of the device, the superconducting ring with a weak link, and is therefore intimately related to the thermal fluctuations in the ring. Not considering external noise, the superconducting ring and the tank circuit together with the preamplifier should exhaust the important sources of noise in the flux detector.

ISSN:0021-8979    

DOI:10.1063/1.1662830

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple point‐contact tunneling device for examination of the properties of almost any metal, alloy, or compound of almost any shape is described. The device has a small mass to permit dipping into liquid helium directly from room temperature. The stability and accuracy of the drive mechanism permit it to be used for single‐particle superconductive tunneling as well as for Josephson devices, weak links, and metal‐metal bridges. Experimental results showing a recording of the drive characteristics of the differential screw, the transition from Josephson weak‐link behavior to single particle tunneling for a Nb&sngbnd;I‐Vycor (Pb) sample, a well‐resolved energy gap for niobium, and the phonon structure of lead are presented.

ISSN:0021-8979    

DOI:10.1063/1.1662831

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The magnetization and the Mo¨ssbauer effect were studied for Tm2Fe17as a function of temperature in the range 4.2–350 K. The results indicate a magnetic phase transition near 72 K.

ISSN:0021-8979    

DOI:10.1063/1.1662832

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Magnetization curves of MnBi thin films have been measured in the temperature range between room temperature and 77°K. Films were prepared on glass substrates with a protection layer of SiO2by vacuum deposition. There occurs a large thermal hysteresis of the magnetization curves, which has not been known of bulk specimens. The magnetic domain configuration at 77°K and the dependence of magnetic anisotropy energy on temperature were also studied. The thermal hysteresis is due to some relaxation mechanism. It is suggested that a thermomagnetic writing other than the Curie‐point writing will be possible, if the thermal hysteretic property is made use of.

ISSN:0021-8979    

DOI:10.1063/1.1662833

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The imaginary longitudinal susceptibility &khgr;″ of polycrystalline YIG in a strong rf magnetic field with amplitudehbehaves according to the average sizex¯of the grain size distributionp(x), to its standard deviation &sgr;, and to the impurities' concentrationc. The threshold fieldh¯cincreases withcand with decreasingx¯. The slope of the tangent to &khgr;″ throughh¯cdecreases with increasingh¯cwhile, ifh¯cis constant, it increases with the impurity content. Taking into account Schlo¨mann's expression for &khgr;″ for a single crystal and a modification of Patton's transit‐time‐limited spin‐wave lifetime model, formulas for &khgr;″ andh¯cfor an impurity‐doped polycrystalline aggregate of spheres having lognormally distributed diameters are worked out. A graphical method to infer the relevant parameters from the experiment is presented. Experimental data and theory are compared on two pairs of compositions; the first one exhibiting a moderateh¯c(∼ 15 Oe) and a second one, a highh¯c([inverted lazy s] 40 Oe). Each pair consists of a fine‐grained YIG and an impurity‐doped YIG. The agreement is qualitatively satisfactory. The modifications resulting from Scotter's inclusion/porosity scattering model are also briefly treated.

ISSN:0021-8979    

DOI:10.1063/1.1662834

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Parallel pumping in the region below 500 MHz provides a convenient tool for measuring the elastic and magnetic relaxation parameters of low‐loss ferrities and garnets. This frequency region is of particular interest in microwave acoustic and cylindrical domain applications and is not readily accessible by conventional resonance and pulse‐propagation techniques. We find that the usual treatments of parallel pumping, in which the normal modes are considered to be plane waves, fail at low frequencies because of multiple surface reflections. A theory is developed which does not contain the plane‐wave assumption and is found to agree with our experimental results for YIG. Our experiments were performed at room temperature with a pump frequency of 42 MHz. The magnetic relaxation parameter determined from these experiments is two orders of magnitude larger than the value that would be deduced from microwave uniform‐precession resonance measurements and is in accord with the domain wall mobility measurements of Hagedorn and Gyorgy, Wanas, and Vella‐Coleiroet al.

ISSN:0021-8979    

DOI:10.1063/1.1662835

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

BaFe12O19particles were prepared by chemical precipitation and ordinary powder metallurgy methods. These particles were oriented in paraffin wax and the angular variation of coercive force was measured. By using the modified equation of Buessemet al., its variation was analyzed. It was found that reverse‐domain nucleation greatly influences the intrinsic coercive force of BaFe12O19particles; even stress‐free chemically precipitated single‐domain particles were influenced. Annealing the ball milled powder raised the coercive force drastically. This is due to the reduction of defect‐nucleation centers. It should be noted that by the chemical precipitation method a coercive force of 6000 Oe was obtained, which is one of the highest reported up to this time for isotropic BaFe12O19.

ISSN:0021-8979    

DOI:10.1063/1.1662836

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Under usual conditions the domain configuration in rare‐earth orthoferrites shows no contrast by x‐ray diffraction topography. In the reorientation range of temperatures, where the net magnetization rotates away from thecaxis, the domain configuration is favorable for x‐ray observations. Domains have been revealed in a cobalt‐substituted orthoferrite where the reorientation range is at room temperature. The observed contrast does not obey the simple rules that apply to similar observations in Fe&sngbnd;Si and YIG. Possible reasons for the observed contrast are discussed in terms of the domain distortion.

ISSN:0021-8979    

DOI:10.1063/1.1662837

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

When electron beams are to be rapidly and accurately deflected by magnetic means, there are some cases in which the deflection yoke is surrounded by a conducting magnetic tube. Eddy currents are set up in the tube which result in time‐dependent positional errors. A simplified treatment of the problem shows how the positional errors can be reduced by means of compensating coil pairs or hybridized saddle‐toroidal yokes.

ISSN:0021-8979    

DOI:10.1063/1.1662838

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

18O diffusion coefficients were measured directly and without serial sectioning, using proton activation analysis of18O via the nuclear reaction18O (p, &agr;)15N. In this technique, the &agr;‐particle spectrum recorded during proton irradiation is used to determine the18O concentration profile; submicron resolution can be achieved. The suitability of this approach was demonstrated by studying oxygen self‐diffusion along thecaxis of ZnO single crystals. In the temperature range 940–1140°C and atPo2of 700 mm,D=1.2(−0.6+1.1)10−10exp[−(29.6±1.6) kcal/RT] (cm2/sec).The results are interpreted as indicating extrinsic behavior; the activation energy is then that for oxygen mobility only. The surface exchange coefficient, characteristic of the reaction between gaseous and lattice oxygen, was also determined, in the temperature range 940–1040°C, asK=5.7(−4.6+23.8)105 exp[−(91.2±4.0 kcal)/RT] (cm/sec).A detailed analysis of the technique is presented. Using a convolution procedure, the oxygen self‐diffusion coefficient, at a given temperature, is determined in a single irradiation run with a precision better than 10%, which is limited only by counting statistics. However, uncertainty in the values of the stopping powers for protons and alphas may cause an additional systematic uncertainty inDof up to [inverted lazy s]50%; since this error is identical for all temperatures, it causes an uncertainty in the preexponential but not in the activation energy. The technique is optimum for determiningDin the range [inverted lazy s]5 × 10−12−[inverted lazy s]5 × 10−17cm2/sec and is useful for testing models of the exchange kinetics.

ISSN:0021-8979    

DOI:10.1063/1.1662839

出版商:AIP    

年代:1973

数据来源: AIP