Spin dependent tunneling at finite bias

Abstract

Results of theoretical studies of spin dependent tunneling in magnetic tunnel junctions at finite bias are presented. A simple model which extends Slonczewski’s ideas is developed. For each spin it assumes tunneling from a single free electron band through a simple barrier. The model predicts a decrease in conductance ratio with bias in good agreement with experimental observations. We find that the decrease of the magnetoconductance ratio, universally seen in experiment, has an intrinsic component resulting from the underlying electronic structure.

Band Structure and Density of States Effects in Co-Based Magnetic Tunnel Junctions

“…By a careful analysis of the conductance-voltage (dI͞dV -V ) and magnetoresistance-voltage characteristics, in combination with 59 Co nuclear magnetic resonance (NMR) to directly investigate local physical structure, we show experimentally that junctions with electrodes of two different crystalline phases show obviously asymmetric transport characteristics. The observed asymmetries can be qualitatively explained by a model developed by us [13][14][15] based on ballistic tunneling between the calculated band structures (and resulting DOS) of fcc-Co and hcp-Co. Furthermore, these experimental and theoretical results may explain several related observations of similar conductance asymmetries [8,[16][17][18].…”

“…Since the differential TMR more strongly decreases at the position of the shoulder and local minimum, one expects that either the minority DOS increases or the majority DOS decreases. As we will show, the dip and shoulder features found in dI͞dV͑V ͒ can be accounted for theoretically by a combination of band structure and DOS arguments, incorporated into a ballistic model of tunneling [13][14][15].…”

“…The key input for the model used [13][14][15] is the spinresolved DOS of the electrodes. The calculated DOS for fcc-Co [13] shows that the total DOS is negatively polarized at E F , but that the s-DOS is positively polarized.…”

Magnetic tunnel junctions with a zinc oxide–cobalt oxide composite tunnel barrier

“…26 Indeed, those parameters could not be extracted from fitting the I͑V͒ curves as it is done commonly. To model the electrode bands, we used the parameters proposed by Davis et al 27 It appears clearly in Fig. 3 that all features described in Fig.…”

Bias voltage dependence of the magnetoresistance in ballistic vacuum tunneling: Theory and application to planarCo(0001)junctions

“…40 In their work, however, the electronic structure of the Fe electrodes was approximated by plane waves, whereas the barrier was assumed as step-like with a linear drop. Although conceptual similar, our approach goes beyond that work.…”