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Full-Text Articles in Physics

Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach Dec 1971

Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach

David Sellmyer Publications

Magnetic breakdown in the basal plane of Be was investigated in fields up to 150 kG. Geometrical aspects of the open orbits caused by breakdown are discussed. An estimate of 30 kG for the characteristic breakdown field is obtained by applying the theory of Falicov et al. Shubnikov-de Haas frequency measurements are reported for the central-cigar cross section. These measurements are relevant to a recent conjecture that the Onsager-Lifshitz quantization scheme may be violated in the presence of magnetic breakdown.


De Haas-Van Alphen Effect In Dilute Beryllium-Copper Alloys , I.S. Goldstein, David J. Sellmyer, B.L. Averbach Sep 1970

De Haas-Van Alphen Effect In Dilute Beryllium-Copper Alloys , I.S. Goldstein, David J. Sellmyer, B.L. Averbach

David Sellmyer Publications

The de Haas-van Alphen effect was investigated in pure beryllium and in Be-Cu alloys containing up to 0.34 at.% Cu. The extremal cross-sectional areas of the cigar-shaped third-band electron pieces of Fermi surface decreased with alloying. The areas of the coronet-shaped second-band hole piece increased with alloying. The magnitude of the area changes were compared with rigid-band-theory predictions. Corrections for lattice-parameter changes were included when possible. In the low-concentration limit, the theory is able to account for the observed area changes. For the highest-concentration alloy, there are deviations, for all areas measured, to greater changes than are predicted by the …


Fermi Surface Of Ausb2. I. High-Field Galvanomagnetic Effects, J. Ahn, David J. Sellmyer Feb 1970

Fermi Surface Of Ausb2. I. High-Field Galvanomagnetic Effects, J. Ahn, David J. Sellmyer

David Sellmyer Publications

High-field galvanomagnetic effects have been investigated in the pyrite structure metallic compound AuSb2 in fields up to 150 kG. The resistance ratios of the samples [ρ(295°K)/ρ(4.2°K)] were as high as 520. The results indicate that AuSb2 is a compensated metal and that its Fermi surface supports open orbits in 〈100〉, 〈110〉, and 〈112〉 directions. At fields higher than about 50 kG, the tendency toward saturation caused by the open orbits changes to a field dependence approaching quadratic, and rather large-amplitude quantum oscillations in the magnetoresistance appear. This behavior is explicable in terms of a loss of the open …


A Technique For The Rapid Measurement Of Thermoelectric Power, G.R. Caskey, David J. Sellmyer, L.G. Rubin Oct 1969

A Technique For The Rapid Measurement Of Thermoelectric Power, G.R. Caskey, David J. Sellmyer, L.G. Rubin

David Sellmyer Publications

A new technique is described for rapid measurement of the thermoelectric power of rod-shaped specimens over a wide temperature range. The apparatus utilizes sensitive commercial dc amplifier for the sample and temperature gradient voltages and a multiple-point recorder for sampling these voltages as well as the sample temperature signal. The technique eliminates spurious thermal emf's in the leads and is based upon on-the-run recording of the sample and temperature gradient voltages as the temperature gradient slowly increases. As a test of this technique, the thermopower of pure nickel was measured between 4.2 and 300 K and the results are compared …


High-Field Galvanomagnetic Properties Of Aual2, Auga2, And Auin2, J.T. Longo, P.A. Schroeder, David J. Sellmyer Jun 1969

High-Field Galvanomagnetic Properties Of Aual2, Auga2, And Auin2, J.T. Longo, P.A. Schroeder, David J. Sellmyer

David Sellmyer Publications

Measurements of the magnetoresistance and Hall voltage have been made in the high-field region on the metallic fluorite compounds AuAl2, AuGa2, and AuIn2. The results have been compared with those expected from the nearly-free-electron (NFE) model. These compounds are uncompensated. The magnetoresistance measurements in principal planes and directions, with one exception, support the NFE model, but the dimensions of the two-dimensional areas of aperiodic open orbits show pronounced deviations. Hall-effect measurements for B in the 〈100〉 and 〈111〉 directions indicate significant departures of the real Fermi surface from the NFE model. A proposed empirical …


Local Moment Formation And Resistivity Minima In Coal Alloys, G.R. Caskey, David J. Sellmyer Mar 1969

Local Moment Formation And Resistivity Minima In Coal Alloys, G.R. Caskey, David J. Sellmyer

David Sellmyer Publications

Measurements of electrical resistivity, thermoelectric power, and magnetoresistance have been made from 1.4° to 300°K in alloys of 48%–57% cobalt in aluminum. At the equiatomic composition, CoAl has the CsCl structure. Resistance minima were observed in the vicinity of 30°K for cobalt concentrations between 50.4% and 51.5%. Below the resistance minima there is a temperature region where the dependence is approximately logarithmic before it saturates at about 1.4°K. The depth of the minima [ρ(1.4°K)– ρ( Tmin)] and the thermopower at 4.2°K both show rather sharp peaks as a function of concentration in the vicinity of 50.5% cobalt. The …


High-Field Magnetoresistance Of Ordered Beta Brass , David J. Sellmyer, J. Ahn, J.-P. Jan Sep 1967

High-Field Magnetoresistance Of Ordered Beta Brass , David J. Sellmyer, J. Ahn, J.-P. Jan

David Sellmyer Publications

The magnetoresistance of several single-crystal specimens of ordered β-brass has been investigated in fields up to 150 kG. The purity of the samples is sufficiently high (ρ2954.2≃400) that the high-field condition is satisfied. The results indicate that ordered β-brass is an uncompensated metal and that its Fermi surface is multiply connected. Strong open orbits were observed when the field was in {110} or {100} planes, and this behavior is compatible with the Fermi-surface model predicted by augmented-plane-wave and Green's-function energy-band calculations. Evidence for the existence of higher-order open orbits and two-dimensional regions of open orbits is …


Low Temperature Sample Orienting Device With Two Degrees Of Freedom, David J. Sellmyer Mar 1967

Low Temperature Sample Orienting Device With Two Degrees Of Freedom, David J. Sellmyer

David Sellmyer Publications

The purpose of this note is to describe a sample orienting device which has been used successfully at liquid helium temperatures to measure the high-field magnetoresistance of several single-crystal metallic compounds in a solenoidal field.