A dc torsional magnetometer for use in high magnetic fields is described. It provides several significant advantages over an earlier device, both by its increased sensitivity and better damping, and also, in particular, because its design allows a torque to be introduced electrostatically. This makes it possible to compensate for monotonic background signals, and to provide a ‘‘transfer standard’’ between calibration and operating conditions. An example is given of its use in the study of the de Haas–van Alphen effect in a single-quantum-well two-dimensional electron system.

New Fourier expansions for the Fermi-surface radii of copper, silver, and gold have been obtained on the basis of high precision de Haasvan Alphen data. The radii agree with the values quoted by Halse to better than 0.2% except for gold near the (100) direction, where the Halse values are about 0.6% too large.

In earlier work, the absolute thermo-electric force, E of the alkalis was measured from about 60°K down to about 4°K. The absolute thermo-electric power ( S=dE/dT ) could then be derived with fair accuracy down to perhaps 8°K. The thermo-electric power of all the alkali metals has now been measured directly between 2 and 20°K, and the Thomson heats derived therefrom. The results are compared with the theory both of the ‘normal’ thermo-electric power and the Gurevich or ‘phonon-drag’ effect. It is clear from the work that experiments below 1 °K in this field will be of much interest and a programme has been started in this temperature range.

Surface relief gratings with submicrometer periods have been fabricated in silica by ion implantation with a focused ion beam, followed by etching in diluted hydrofluoric acid. Implanted silica etches three times faster than unimplanted silica and groove depths of the order of 300 nm have been achieved. The method does not require photolithography or masking layers, allows arbitrary patterns to be defined, and may be used to fabricate diffractive optical elements or grating filters in optical waveguides.

The de Haas-van Alphen effect has been studied in the Kondo system Cu:Cr in magnetic fields up to 55 kG at 1.0 K. In alloys containing ~30 ppm Cr "beat" minima and shifts of the spin-splitting zeros are observed for several orbits. These observations are explained by supposing the normal spin splitting of the Landau levels to be modified by an antiferromagnetic exchange term, so that the effective g factor becomes g-^€ ex /iJ. B H, Some time ago we reported 1 the observation of a sharp minimum in the amplitude of (111) "belly" de Haas-van Alphen (dH-vA) oscillations in very dilute (~30 ppm) Cu:Cr alloys. The effect had the appearance of a "beat" minimum, but could not be ascribed to sample imperfection, so we postulated at the time the existence of an electronscattering anomaly. It now appears probable that we are indeed observing a form of beat and that this is fundamental in origin.The frequencies observed in the dH-vA effect can be related to an extremal area of the Fermi surface and are associated with the spacing of the Landau levels for that cross section. The amplitude of the oscillations is a complex function of magnetic field H and temperature T but is also affected by the electron spin. Each of the Landau levels is split according to the spin direction, introducing into the amplitude a term cos(TTgm*/2m 0 ), where the factor g is usually but not always 2 and m*/m 0 is the cyclotron mass in units of free-electron mass. When the spin splitting is exactly half the spacing of the Landau levels, the amplitude of the fundamental drops to zero; this corresponds to gm*/m 0 taking the value 1, 3, etc.In ferromagnetic systems such as iron, 2 nickel, 3 or palladium with a small concentration of cobalt, 4 an exchange interaction splits the Fermi surface into separate spin-up and spin-down surfaces (with corresponding extremal areas) and the spin-splitting factor is suppressed. This feature is particularly striking in the experiments of Hornfeldt, Ketterson, and Windmiller, 4 where small concentrations of cobalt added to palladium suppressed the spin-splitting zeros, and the nesting spin-up and spin-down Fermi surfaces caused a beat in the dH-vA oscillations. This experiment suggested that we reinterpret our data for Cu:Cr in terms of a beat induced by the localized moment. We used for new experiments a single crystal of copper doped with 35 ppm (nominal) chromium. The resistance ratio of the specimen (room temperature to 4.2 K) was 42, giving a value of 34 ppm using the resistivity data of Daybell and Steyert. 5