Stoner–Wohlfarth model applied to bicrystal magnetoresistance hysteresis

Abstract

We calculate numerically the magnetization direction as function of magnetic field in the StonerWohlfart theory and are able to reproduce the shape of the low-field magnetoresistance hysteresis observed in manganite grain boundary junctions. Moreover, we show that it is necessary to include biaxial magnetocrystalline anisotropy to fully describe the grain boundary magnetoresistance in La0.7Sr0.3MnO3/SrTiO3 bicrystal tunnel junctions.Can the fairly simple model presented by Stoner and Wohlfart in 1948 [1] provide insights in the processes that occur in manganite bicrystal grain boundary junctions? In the following we show how the coherent rotation of the magnetization vector can explain the characteristic features in the field dependence of the magnetoresistance.Recently, a substantial low-field magnetoresistance was observed in grain boundaries of perovskite manganites [2,3] and other half-metallic ferromagnets [4,5]. In order to understand and exploit this effect several studies have used bicrystal grain boundary junctions [6,7,8]. Since bicrystals are samples with well defined crystal orientations with respect to an interface, they are in a way ideal systems for studies of the behaviour of magnetic tunnel junctions. Traditionally, the conductivity of magnetic tunnel junctions is compared with Julliere's model [9], in which the tunneling magnetoresistance is determined by the spin polarization of the electrodes. A more realistic scenario was considered by Slonczewski [10], who used a method to match the wave functions across the tunneling barrier. He derived an expression for direct tunneling through the interface which includes the angle between the directions of the magnetization of the electrodes.

Magnetization reversal processes in magnetic bicrystal junctions

“…25. Figures 5͑e͒-5͑g͒ show how the magnetoresistance hysteresis varies with misorientation angle, as obtained from simulations using our model 25 for the present geometry. Each simulation starts from the saturated state in one field direction, and then the direction of magnetization is traced for decreasing fields through zero to saturation in the opposite field direction.…”

“…Details of the model can be found in Ref. 25. Figures 5͑e͒-5͑g͒ show how the magnetoresistance hysteresis varies with misorientation angle, as obtained from simulations using our model 25 for the present geometry.…”

“…The model presented in Ref. 25 is essentially two dimensional and does not allow for M to be directed out of plane. The magnetic behavior of samples A-C can be analyzed within this model.…”

Magnetoresistance in bicrystal grain-boundary junctions analyzed within the Stoner–Wohlfarth model

“…We have previously shown that with the field along the strip line ðB ? GBÞ the magnetoresistance hysteresis can be analyzed within the Stoner -Wohlfarth model for reversal by coherent rotation of magnetization [3]. A typical result from simulations of the bicrystal magnetoresistance is shown in the inset of Fig.…”

“…The inset shows a simulated hysteresis using the Stoner-Wohlfarth model with the angles a ¼ 60 and b ¼ 90 as described in Ref. [3]. electrodes behave as single domains, and that the magnetization reversal process is determined by the coherent rotation of the direction of magnetization in each of the electrodes.…”