75% inverse magnetoresistance at room temperature in Fe4N/MgO/CoFeB magnetic tunnel junctions fabricated on Cu underlayer

Pseudo-single-crystal Cu underlayer (UL) with thermal tolerance was obtained on bare Si wafer by employing a diffusion-blocking layer. Fe4N layer fabricated on the Cu UL has an epitaxial relationship and a large grain diameter. Magnetic tunnel junctions in a stacking sequence of Fe4N/MgO/CoFeB exhibited an inverse tunnel magnetoresistance (TMR) effect at room temperature. The largest magnitude of the TMR ratio, −75.1%, was obtained at bias voltage Vb=−250 mV, where electrons flow from CoFeB to Fe4N. The large inverse TMR ratio is due to the improvement of the crystallinity of the Fe4N film because of the small lattice misfit between Fe4N and Cu.