State diagram of a perpendicular magnetic tunnel junction driven by spin transfer torque: A power dissipation approach

Abstract

The state diagram of a magnetic tunnel junction with perpendicularly magnetized electrodes in the presence of spin-transfer torques is computed in a macrospin approximation using a power dissipation model. Starting from the macrospin's energy we determine the stability of energy extremum in terms of power received and dissipated, allowing the consideration of nonconservative torques associated with spin transfer and damping. The results are shown to be in agreement with those obtained by direct integration of the Landau-Lifshitz-Gilbert-Slonczewski equation. However, the power dissipation model approach is faster and shows the reason certain magnetic states are stable, such as states that are energy maxima but are stabilized by spin transfer torque. Breaking the axial system, such as by a tilted applied field or tilted anisotropy, is shown to dramatically affect the state diagrams. Finally, the influence of a higher order uniaxial anisotropy that can stabilize a canted magnetization state is considered and the results are compared to experimental data. I.To analytically compute the stability of each state, the Landau-Lifschitz-Gilbert equation with two STT terms is used (Eq. 1). It describes the dynamics of the magnetization under an effective magnetic field and a bias voltage:

Magnetic aftereffects in CoFeB/Ta/CoFeB spin valves of large area

“…9). This fact was confirmed by direct MOKE measurements in [8]. The bubbles can be stabilized by the demagnetizing field generated by the surface magnetic charge against the applied field [20,42].…”

“…In the present paper, we will pay attention to another problem, which dramatically affects the quality of the large (∼1-10 mm 2 ) area of CoFeB multilayered structures. Thin ferromagnetic layers as well as CoFeB multilayered structures manifest slow magnetic relaxation due to domain-wall dynamics [8]. In [8], magneto-optic Kerr effect (MOKE) microscopy of those samples studied in this paper was reported.…”

“…Thin ferromagnetic layers as well as CoFeB multilayered structures manifest slow magnetic relaxation due to domain-wall dynamics [8]. In [8], magneto-optic Kerr effect (MOKE) microscopy of those samples studied in this paper was reported. This process is very complicated due to the thermally activated character of the domain-wall unpinning, peculiar interaction between ferromagnetic layers, and inhomogeneous distribution of magnetization through the layer [ Fig.…”

Asymmetric Magnetization Switching in Perpendicular Magnetic Tunnel Junctions: Role of the Synthetic Antiferromagnet’s Fringe Field

“…We also considered the As already demonstrated in order to reproduce the experimental state diagram using an analytical or numerical modeling the uniaxial symmetry needs to be broken. In the present computation we have introduced a tilt of 0.6 degree in the magnetocrystalline anisotropy axis that is sufficient to break the uniaxial symmetry [32].We have been able to follow the magnetic configurations during the STT driven magnetization switching, as seen in figure 3 c,d,e,f. This allows us to compare the nucleation points of the reversal depending on the transition.…”

“…Figure 2a) shows the energy barrier dependence as a function of the applied field for the two SAF configurations, compensated on the left (low fringe field) and saturated on the right (large fringe field). Figure 2b) displays the corresponding state diagrams obtained by recording the switching voltage as a function of the applied field for both transitions and both configurations as described in Ref [30][31][32]. Insets are schematics of the stack magnetic configurations.…”