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The magnetic ternary compound UNi,Si, has been studied by means of magnetic susceptibility, thermoelectric power and low-temperature (1.5-29 K) specific heat measurements. The magnetic susceptibility is Curie-Weiss-like above 130K and bemmes highly anisotropic at lower temperatures. Distinct features associated with the 103 and 53 K phase transitions are observed while deviation from Curie-Weiss behaviour occurs near the 173 K phase transition. The thermoelectric power from oriented samples is also anisotropic, a,ith thec-component strongly wupledto the threemagnetic phase transitions. Thegammavalue obtained from the specific heat measurements is 2 2 d mol-' K-' which indicates a small massenhancement in thissystem.

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We report a study of transverse magnetoresistance of thin, rolled potassium films. The measurements in the Sondheimer geometry, when the magnetic field is along the outwards normal to the plane of the film, yield no oscillatory pattern in the transverse magnetoresistance as a function of increasing field. For the high-field regime, with w t = 10-30, there is a non-saturating linear increase in the magnetoresistance. The Kohler slope of this increase is dependent on the ratio of the film thickness to the electronic mean free path and is up to 20 times the appropriate slope for the bulk metal. From a comparison of these results with the data available for the MacDonald geometry (with the field lying in the film plane), we deduce that the origin of the magnetoresistance increase for the Sondheimer geometry is related to size effects. We discuss several possible explanations for the absence of Sondheimer oscillations, such as a large Hall field, open orbits due to the preferred orientation of the @domains associated with charge-density waves and inherent bulk magnetoresistance. None of them seems to provide a sufficient argument for the absence of the oscillatory pattern in the field dependence of the transverse magnetoresistance in the potassium thin films under study.