A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions

摘要

We investigated the spin-dependent transport properties of Fe/MgAl2O4/Fe(001)magnetic tunneling junctions (MTJs) on the basis of first-principlescalculations of the electronic structures and the ballistic conductance. Thecalculated tunneling magnetoresistance (TMR) ratio of a Fe/MgAl2O4/Fe(001) MTJwas about 160%, which was much smaller than that of a Fe/MgO/Fe(001) MTJ(1600%) for the same barrier thickness. However, there was an evanescent statewith delta 1 symmetry in the energy gap around the Fermi level of normal spinelMgAl2O4, indicating the possibility of a large TMR in Fe/MgAl2O4/Fe(001) MTJs.The small TMR ratio of the Fe/MgAl2O4/Fe(001) MTJ was due to new conductivechannels in the minority spin states resulting from a band-folding effect inthe two-dimensional (2-D) Brillouin zone of the in-plane wave vector (k//) ofthe Fe electrode. Since the in-plane cell size of MgAl2O4 is twice that of theprimitive in-plane cell size of bcc Fe, the bands in the boundary edges arefolded, and minority-spin states coupled with the delta 1 evanescent state inthe MgAl2O4 barrier appear at k//=0, which reduces the TMR ratio of the MTJssignificantly.