The high-magnetic-field properties of some refractory carbides were investigated at low temperatures. The upper critical fields for NbC, a solid solution of 40% NbC-60% TaC, and TaC are between 4.2 and 21.3 kG; MoC, M056C44, and Mo 6 oC4o+2% VC have upper critical fields between 80 and 120 kG; and Mo 3 Al 2 C has an upper critical field of 156 kG at 1.2°K. Mo 3 Al 2 C is the only known superconductor with the 0-Mn crystal structure. From the available data the electronic specific-heat coefficient 7, the thermodynamic critical field H c , the Ginzburg-Landau parameter K, and the lower critical field H c \ were estimated at the experimental temperatures.

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takes place whenf(w) = (jOrr/sq, an equation that can be solved graphically to obtain the frequency wd where the acoustic and electromagnetic branches are degenerate. Ordinarily this transcendental equation possesses only one real root. However, there is a range of the magnetic field for which it can have up to three real roots. In this Letter we shall limit ourselves to the former situation. By treating the right-hand side of Eq. (5) as a perturbation, the solution for the eigenfrequencies at the crossover to first order in O 0 is For a metal such as sodium in a magnetic field of the order of 5xl0 4 G, the crossover frequency u) d is approximately equal to 3.6xl0 9 sec" 1 . The splitting at this point is about 12% of u^. The considerable admixture of acoustic and helicon modes in this region suggests the possibility of exciting transverse phonons in metals by means of electromagnetic radiation of the appropriate frequency. In Fig. 1 we give a graphical representation of the zeros of Eq. (5) in terms of the parameter w =qvQAV For tlie purpose of this calculation we have considered sodium at aThe Fermi surfaces of nonferromagnetic metals have been extensively investigated by de Haas-van Alphen (dHvA) and related techniques. Corresponding data on the magneto-oscillatory properties of ferromagnetic metals are much less complete, although preliminary dHvA effect results on Fe have been reported by Anderson and Gold, 1 and Shubnikov-de Haas oscillations have been detected in Co by Fawcett and Reed. 2 In this Letter we describe dHvA oscillations observed in nickel single crystals by means of a null deflection torsion balance in steady magnetic fields up to 40 kG. The dHvA oscillations were studied as a function of magnetic field orientation in the (001) and (11~0) crystallographic planes. The variation of the period of the oscillations in these planes suggests that at least one sheet of the Fermi surface of nickel is similar to that of the noble metals, in accord with a model of the Fermi surface proposed by magnetic field for which w at the crossover is Wfi = 2. Under this assumption £ 0 = 4.8 x 10 4 G i-and/(w^) = 0. 684. The foregoing results are, of course, only valid if CU 0 T » 1. Further details of this work will be the subject of a subsequent publication.The authors would like to thank J. Bok and D. N. Langenberg for communicating their results 6 prior to publication, M. Lampert for many helpful suggestions, and K. M. Brown for kindly assisting with the numerical calculations.Fawcett and Reed on the basis of magnetoresistivity studies.The torsion balance used for this study was modified so that the large steady torques exerted on the sample due to the ferromagnetic anisotropy of nickel could be nullified. Samples were cut from a single crystal nickel rod [p(300°K)/ p(4.2°K)*990] in the form of disks (0.20-in. diamx0.030 in. thick) and each was mounted with its axis of rotation vertical. In the first sample the [110] axis coincided with the disk axis, so that the magnetic field was located in the (1 TO) plane....

A detailed investigation of the Hall mobility has been carried out on a series of [inverted lazy s]2-μ-thick n-type {001} Si/{011̄2} Al2O3 films. A specially designed Hall bridge pattern has been used to obtain independent measurements of mobility as a function of current direction in the plane of the film. The data show an anisotropy in the mobility of approximately 9%, with a maximum in mobility occuring along the 〈100〉 Si direction that is parallel to the 〈21̄1̄0〉 Al2O3 direction in the plane of the substrate. This behavior is found to be a consequence, through the piezoresistance effect, of the anisotropic thermal contraction of Al2O3 on cooling from the deposition temperature, which leads to an anisotropic thermally induced stress in the Si.

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