Temperature dependence of magnetoresistance and surface magnetization in ferromagnetic tunnel junctions

Abstract

The temperature dependence of spin-polarized tunneling is investigated between 77 and 420 K for various ferromagnetic tunnel junctions. Both the junction resistance and the magnetoresistance decrease with increasing temperature $T.$ The experimental results are successfully described by a model that includes two current contributions. The dominant one is elastic, spin-polarized tunneling between the two ferromagnetic electrodes, each with an electron polarization $P$ that decreases with $T$ due to thermally excited spin waves according to $P\ensuremath{\propto}(1\ensuremath{-}\ensuremath{\alpha}{T}^{3/2}),$ i.e., in the same way as the surface magnetization. A smaller second conductance is due to assisted, spin-independent tunneling which we find to be proportional to ${T}^{1.35\ifmmode\pm\else\textpm\fi{}0.15}.$