An investigation op the electrical resistance of thin films of rare earth metals

Abstract

Measurements have been made of the electrical resistivity in the film plane of rare earth metal films over a thickness range of 130 A to 250O A. The films are deposited onto glass substrates by high vacuum evaporation at pressures better than 10(^-6) torr and are protected by an over coating of silicon monoxide. The resistivity has been examined between 4.2 K and room temperature; the magnetoresistance has also been studied in the presence of applied transverse fields up to 15 KOe and longitudinal fields up to 10 KOe. The variation of resistance with temperature is similar in form to that obtained for bulk specimens for all film thicknesses. However, in films less than about 400 A thick, the spin-disorder resistivity shows a pronounced decrease in magnitude but the degree of variation did not appear to be consistent with thickness. The spin-disorder resistivity is obtained by computing a least-squares fit to the linear high temperature part of the resistance curve and extrapolating to 0 K. The results show that in the temperature region where spin-wave theory is applicable, at very low temperatures pspin ɚ T(^2) in accordance with spin-wave theory but at higher temperatures, this falls off, so that It is found that pspin ɚ T(^2) in the first case, the variation of Pspin(T) can be better explained in terms of an anisotropy energy gap and the change to a T(^3/2) proportionality has been related to the behaviour of the spontaneous magnetization and the anomalous Hall effect. In addition, the variation of pSpin of dysprosium is examined in detail and it is suggested that the observed fall off of spin resistivity with thickness, which can be extrapolated to zero at zero thickness, is related to the variation of magnetization with thickness in the film. Finally, magnetoresistive studies detected negative effects with fields applied transversely to the electric field. The anomalous peak at the Neel point is suppressed in dysprosium and terbium and a small demagnetizing field effect is observed in dysprosium.