A phenomenological description of temperature dependence of magnetoresistance in La2/3Ca1/3MnO3-δ 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 phenomenofogical formula of\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$\rho (T) = \frac{1}{{\sigma (T)}} = \frac{1}{{(M/M_s )^2 + \beta ( - E_0 /k_B T)}}$$ \end{document} where the fitting parameters α, β vary as the external magnetic fieldH changes,E0 is the activation energy,E0/kB = 1160 K,Ms is the saturation magnetization, the temperature and magnetic field dependence ofM/Ms is obtained by the mean-field expression.