S. Legvold

Low‐Temperature Thermoelectric Power of the Rare‐Earth Metals

The Seebeck coefficients (thermoelectric powers) of yttrium, lanthanum, and 11 of the rare earths have been measured for the temperature range 7° to 300°K. The transitions reported by other investigators on specific heat, magnetic moment, and resistivity at the magnetic ordering temperatures are, in many instances, visible also in the curves of thermoelectric power (TEP) vs temperature. The Neel temperature is evidenced by a change in slope in the TEP vs T curve. The ferro‐antiferro transition temperature is obvious only in the case of dysprosium and appears as a sharp drop in the curve. With the exception of samarium and ytterbium, the TEPs of the metals are negative throughout most of the temperature range covered, and, with the same exceptions, the TEP curves have about the same slope near room temperature.

Collision Excitation of Molecular Vibrations in Halogen‐Substituted Methanes

Departures from the equilibrium between vibrational and translational energies in gases are characterized by relaxation times which depend upon the ease with which vibrations may be excited or de‐excited by collisions. The de‐excitation process has been discussed by various authors on the basis of the relative velocity of approach of two colliding molecules and on the basis of the relative energy of approach.The dispersion of ultrasound has been measured in fourteen halogen‐substituted methanes and compared with existing data. Binary collisions were found to be responsible for the excitation of vibrations, and all the gases were found to have a single relaxation time indicating a strong intermodal coupling. The probability, in a collision, of exciting or de‐exciting molecular vibrations was found to depend upon the relative energy of approach of the molecules. Molecules with the same number of halogen substitutions resemble each other in this respect. The data suggest that the colliding molecules might fo...

Magnetic susceptibility and electrical resistivity of electrotransport purified scandium single crystals from ≈ 1 to 300 k☆

Abstract The magnetic susceptibility of electrotransport purified Sc single crystals was measured from 0.7 to 295 K. Both the easy (χ a ) and hard (χ c ) directions were measured using a microcomputer controlled Faraday apparatus. Above 50 K the present results agree with earlier work on a less pure sample, but below 50 K the present results are lower by as much as 4%. In addition the maximum at ≈ 30 K and the minimum at ≈ 6 K are much more pronounced in the purer material, and the susceptibility increases rapidly as the temperature approaches 0 K. Electrical resistivity measurements were made on the same single crystals from 1.6 to 300 K. The resistance ratios were 365 for the a -axis crystal and 274 for the c -axis crystal. At 300 K, ρ a ≈ 2.5 ρ c .

Magnetic Properties of Gd–Sc Alloys

Magnetic properties of some Gd–Sc alloys have been measured. Paramagnetic to antiferromagnetic to ferromagnetic transitions were observed in the 69 at. % Gd alloy. Alloys of higher Gd content were ferromagnets and those of lower Gd content were antiferromagnets. The paramagnetic Curie temperatures decreased with decreasing Gd concentration. The effective number of Bohr magnetons per Gd atom showed a nearly linear increase with decreasing Gd concentration. Also the saturation magnetic moment per Gd atom increased with decreasing Gd concentration in the case of the ferromagnets.

Temperature Dependence of Sound Dispersion in Halo‐Methane Gases

Sound dispersion has been examined in eight halo‐methane gases near 100°C and 200°C, and four near 300°C. The observed relaxation times have been used along with data obtained previously at room temperature to calculate the vibrational collision lifetimes over this temperature range. The results have been compared with theoretical predictionsof Schwartz and Herzfeld which used an attractive term in the potential to help account for the effect of long‐range forces. Agreement is good, although several lifetimes at room temperature appear somewhat small.

Kondo scattering in a pure metal- beta cerium. II. Theoretical

For pt.I see ibid., vol.6, no.2, p.L49 (1976). A detailed explanation of the anomalous electrical resistivity of beta cerium is given.

Superconductivity in Some Compounds of La, Lu, Sc, and Y

A number of high‐melting‐point rare‐earth compounds have been examined for superconductivity. In this work LaC2, LuC2, and YGa2 were found to be superconductors, but Y3C, LaGa2, La5Sn3, and Y5Sn3 did not exhibit superconductivity in tests down to 1.4 K.

Kondo scattering in a pure metal- beta cerium. I. Experimental

The electrical resistivity of DHCP beta Ce has been found to be anomalously large above 60K and to exhibit an order of magnitude drop below 20K. The magnetic susceptibility exhibits a Curie-Weiss behaviour above 40K, and magnetic ordering occurs at approximately 13K. The large resistivity is thought to be due to Kondo-like spin flip scattering which, at low temperatures, is quenched by the internal field associated with magnetic ordering.

Thermocouples in Magnetic Fields

It is shown that in a cryostat the use of an isothermal path leading out of an applied magnetic field will ensure insensitivity of thermocouples to the magnetic field. Tests in liquid helium in such a cryostat were conducted on a number of thermocouples with the applied field ranging up to 100 kG. The results showed that Cu‐constantan, Cu–Au 0.03 at.% Fe, and Cu–Au 2.1 at.% Co thermocouples are not affected by magnetic fields. In subsequent work up to 300 K the first two thermocouples listed were still insensitive to magnetic fields. The third thermocouple was not tested at the higher temperatures.

Sound dispersion in substituted methane-inert gas mixtures

Binary halomethane—noble gas mixtures were examined ultrasonically. The methanes used were CF4, CHF3, and CCl2F2 and the noble gases were Ar, Ne, and He. Results obtained show that the reciprocal relaxation times for these mixtures vary linearly with the concentration. Also, Ar—X collisions are less effective, He—X collisions are much more effective, and Ne—X collisions differ little from X—X collisions in vibrational energy transfer. X represents the dispersive gas. Theoretical values of Z10AB, the mean collision lifetime of an A molecule in an otherwise pure gas of B molecules, were calculated according to the Schwartz, Slawsky, and Herzfeld theory. Intermolecular potentials appropriate for the treatment of the data were examined, and it was found that the Lennard‐Jones 6:12 potential was appropriate for the noble gases, and the 7:28 form was appropriate for the halomethanes.