86% TMR at 4.2 K for amorphous magnetic-tunnel-junctions with Co₆₀Fe₂₀B₂₀ as free and pinned layers

Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni₇₉Fe₂₁(5)/Ir₂₂ Mn₇₈(12)/Co₆₀Fe₂₀B₂₀(4)/ Al(0.8)-oxide/Co₆₀Fe₂₀B₂₀(4)/ Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co₆₀Fe₂₀B₂₀ alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co₆₀Fe₂₀B₂₀, 55%, was observed in the MTJs after annealing at 270°C for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm², small coercivity H_C of ≤Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V_1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.