Magnetization reversal and current hysteresis due to spin injection in magnetic junction

Abstract

Magnetic junction is considered which consists of two ferromagnetic metal layers, a thin nonmagnetic spacer in between, and nonmagnetic lead. Theory is developed of a magnetization reversal due to spin injection in the junction. Spin-polarized current is perpendicular to the interfaces. One of the ferromagnetic layers has pinned spins and the other has free spins. The current breaks spin equilibrium in the free spin layer due to spin injection or extraction. The nonequilibrium spins interact with the lattice magnetic moment via the effective s-d exchange field, which is current dependent. Above a certain current density threshold, the interaction leads to a magnetization reversal. Two threshold currents are found, which are reached as the current increases or decreases, respectively, so that a current hysteresis takes place. The theoretical results are in accordance with the experiments on magnetization reversal by current in three-layer junctions Co/Cu/Co prepared in a pillar form.PACS: 75.60.Ej; 75.70.Cn.

Current-induced exchange switching magnetic junctions with cubic anisotropy of the free layer

“…The STT contribution becomes unimportant under low threshold of the injection switching magnetic junction, so that we will consider only the injection mechanism below. Under assumptions mentioned, the Landau-Lifshitz equation describing the lattice dynamics of the free layer in the absence of damping has an integral of motion even in presence of a current through the junction [15,16]. Such an integral is the magnetic energy, including the Zeeman energy in applied magnetic field, the anisotropy energy, the demagnetization energy, and the sd exchange interaction energy between conduction electrons and magnetic lattice.…”

Lower current-driven exchange switching threshold in noncollinear magnetic junctions under high spin injection

“…When the spin injection predominates over the spin torque transfer, the LLG equation has the first integral in form of a magnetic energy consisting of the Zeeman energy, the anisotropy energy, the demagnetization energy, and the nonequilibrium sd exchange energy proportional to the spin-polarized current density [8,9]. The magnetic energy is a function of the angles determining orientation of the free layer magnetization with respect to the easy axis of the layer, the external magnetic field, and the pinned layer magnetization (which is parallel to the easy axis of this layer).…”

Surface spin-transfer torque and spin-injection effective field in ferromagnetic junctions: Unified theory

“…where λ = L/l, ξ = x/l and parameter ν characterizes the influence of the layer 3 (typically ν ∼ 1, see [13,14] for details). We substitute (14) into expression (9) and use the variational derivative δ( M1 M(ε))/δM(x) = M1 δ(x − ε). Then we get…”