Electronic transport and Kondo effect in La1-xCex films

The electrical resistivity rho of thin La1-xCex films (50 Angstrom less than or equal to d less than or equal to 4000 Angstrom) has been measured 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 in the La dhcp structure. Films with x = 0.01 show the superimposed effect of superconducting fluctuations and Kondo scattering, yielding a maximum in the magnetoresistance. For x = 0.02, the determined Kondo temperature 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 exchange interaction J between Ce moments and conduction electrons extracted from rho(B) is independent of film thickness d dawn to 100 Angstrom.