ELECTRONIC TRANSPORT AND KONDO EFFECT IN LA1-XCEX FILMS

The electrical resistivity rho of thin La1-xCex films (50 Angstrom les s than or equal to d less than or equal to 4000 Angstrom) has been mea sured in the temperature range 1.4 K less than or equal to T less than or equal to 10 K and in magnetic fields B up to 5 T. The films grow i n the La dhcp structure. Films with x = 0.01 show the superimposed eff ect of superconducting fluctuations and Kondo scattering, yielding a m aximum in the magnetoresistance. For x = 0.02, the determined Kondo te mperature for d = 100 Angstrom is in good agreement with bulk data. In films with x = 0.04 where superconductivity is completely suppressed, evidence of spin-glass order is Found from the negative deviation of rho towards low T compared to the Kondo -1n(T/T-K) behavior. In large magnetic fields where the spin-glass correlations are suppressed, the magnetoresistivity rho(B) shows single-ion Kondo behavior. The exchang e interaction J between Ce moments and conduction electrons extracted from rho(B) is independent of film thickness d dawn to 100 Angstrom.