Resonant spin-dependent tunneling in spin-valve junctions in the presence of paramagnetic impurities - art. no. 064429

The tunnel magnetoresistance (TMR) of F/O/F magnetic junctions (F's are fer romagnetic layers and O is an oxide spacer) in the presence of magnetic imp urities within the barrier, is investigated. We assume that magnetic coupli ngs exist both between the spin of the impurity and the bulk magnetization of the neighboring magnetic electrode, and between the spin of the impurity and the spin of the tunneling electron. Consequently, the resonant levels of the system formed by a tunneling electron and a paramagnetic impurity wi th spin S =1 are a sextet, and the resonant tunneling depends on the direct ion of the tunneling electron spin. At low temperatures and zero bias volta ge, the TMR of the considered system may be larger than that of the same st ructure without paramagnetic impurities. It is calculated that an increase in temperature leads to a decrease in the TMR amplitude due to excitation o f spin-Rip processes resulting in mixing of spin-up and down channels. It i s also shown that asymmetry in the location of the impurities within the ba rrier can lead to asymmetry in I(V) characteristic of impurity-assisted cur rent. Two mechanisms responsible for the origin of this effect are identifi ed. The first one is due to the excitation of spin-hip processes at low vol tages and the second one arises from the shift of resonant levels inside th e insulator layer under high applied voltages.