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 $T.\mathrm{}$ 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 $P\propto \left(1\mathrm{}-\alpha T^{3/2}\right),$ 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 $T^{1.35\pm 0.15}.$

• Received 12 May 1998

DOI:https://doi.org/10.1103/PhysRevB.58.R2917