We investigated the effect of a magnetic field along a hard in-plane axis Hhard on a current-induced magnetization switching (CIMS) in magnetic tunnel junctions (MTJs). Since Hhard causes the effective field to tilt away from the easy axis, we evaluated the Hhard dependence of two contributing factors in CIMS [the intrinsic critical current density (J c0) and the thermal stability factor (E/kBT)] as functions of the tilting angle (θH). Both measurements and numerical simulations showed that the presence of Hhard can reduce J c0 by more than the amount estimated by Slonczewski's polarization function g(θ) by an order of magnitude and that E/kBT is independent of θH. These findings suggest that the effect of Hhard mainly appears in the dynamic properties due to the nonconservative force of the spin-transfer torque based on the Slonczewski's model. A simple stability analysis demonstrated that the tilt of the magnetization direction away from the easy axis caused by the presence of H hard induces an imbalance between the spin-transfer and damping torques and that applying a current achieves the further tilted stable state. Achievement of this stable state can be interpreted as the suppression of the effect of the effective demagnetization field (Hd*). Therefore the major reduction in Jc0 is due to the suppression of Hd* caused by the presence of Hhard.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2011 Nov 23|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics