Fe₄N/MgO/CoFeB強磁性トンネル接合の磁気抵抗効果の温度依存性

抄録

  We investigated the dependence of transport properties of Fe₄N/MgO/CoFeB-magnetic tunnel junctions (MTJs) on temperature. In antiparallel configurations of magnetizations of Fe₄N and CoFeB layers, a convex shaped peak was observed on the differential conductance curve as a function of bias voltage and it became clearer with decreasing temperature. The bias voltage (V_B) of ∼ -200 mV, where the peak was observed, corresponded to the energy where a sharp peak exists in the density of states (DOS) of the minority spin band of Fe₄N. The shape of the differential conductance curves suggested that the contribution of Δ₁ electron tunneling is not significant to total conductance in the Fe₄N/MgO/CoFeB-MTJs differently from that in CoFeB/MgO/CoFeB-MTJs, even though they have a similar crystallized MgO-barrier layer. The asymmetric shape of the dependence of the tunnel magnetoresistance (TMR) ratio on bias voltage did not change in a temperature range from 6 K to 300 K, but the absolute value of the maximum TMR ratio was monotonically increased from 76 % at 300 K to 103 % at 6K. Spin polarization of Fe₄N DOS at the Fermi level was estimated to be -0.5 from the present TMR ratio near zero bias and this was close to the theoretical value of -0.6.