A Phenomenological Description Of Temperature Dependence Of Magnetoresistance In La2/3ca1/3mno3-Delta Thin Films

The electrical resistance in zero magnetic field and magnetoresistance in different external magnetic fields have been measured in a temperature range of 77-300 K. It is found that the temperature dependence of magnetoresistance can be well described by a phenomenological formula of rho(T) = 1/sigma(T) = 1/a(M/M-3)(2) + beta exp(-E-o/k(B)T)' where the fitting parameters alpha, beta vary as the external magnetic field H changes, E-o is the activation energy, E-o/k(B) = 1160 K, M-s is the saturation magnetization, the temperature and magnetic field dependence of M/M-s is obtained by the mean-field expression.