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

概要

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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 (VB) 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.