Currents, torques, and polarization factors in magnetic tunnel junctions

By J. Slonczewski. 2004

374 citations recorded by the source corpus.

Bardeen's transfer-Hamiltonian method is applied to magnetic tunnel junctions having a general degree of atomic disorder. The results reveal a close relationship between magnetoconduction and voltage-driven pseudotorque, and also provide a means of predicting the thickness dependence of tunnel-polarization factors. Among the results: (i) The torque generally varies with moment direction as $\mathrm{sin}\phantom{\rule{0.2em}{0ex}}\ensuremath{\theta}$ at constant applied voltage. (ii) Whenever polarization factors are well defined, the voltage-driven torque on each moment is uniquely proportional to the polarization factor of the other magnet. (iii) At finite applied voltage, this relation implies significant voltage-asymmetry in the torque. For one sign of voltage the torque remains substantial even if the magnetoconductance is greatly diminished. (iv) A broadly defined junction model, called ideal middle, allows for atomic disorder within the magnets and $\mathrm{F}∕\mathrm{I}$ interface regions. In this model, the spin-$(\ensuremath{\sigma})$ dependence of a basis-state weighting factor proportional to the sum over general state index $p$ of ${(\ensuremath{\int}\ensuremath{\int}dydz{\ensuremath{\Psi}}_{p,\ensuremath{\sigma}})}^{2}$ evaluated within the (e.g., vacuum) barrier generalizes the local state density in previous theories of the tunnel-polarization factor. (v) For small applied voltage, tunnel-polarization factors remain legitimate up to first order in the inverse thickness of the ideal middle. An algebraic formula describes the first-order corrections to polarization factors in terms of newly defined lateral autocorrellation scales.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/098c0960988f81afec1da01aed660aacb4ac0d4a

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In Atomic and Molecular Physics, and Optics

Citations in the corpus

Bias-driven high-power microwave emission from MgO-based tunnel magnetoresistance devices (2008, background): “Note that, unlike T p , is related to the exchange coupling energy between the two magnetic layers and does not necessarily cancel out when the voltage is set to zer”
Tunnel Magnetoresistance Over 100% in MgO-Based Magnetic Tunnel Junction Films With Perpendicular Magnetic L1$_{0}$-FePt Electrodes (2008, background): “spin transfer torque (STT) switched magnetoresistive random access memory (MRAM) application [1]–[3].”
Spin-polarised currents and magnetic domain walls (2005, methodology): “Theory of spin-transfer torque in a MTJ device was given by Slonczewski 451 .”
Spin-transfer torque RAM technology: Review and prospect (2012, neutral): “The threshold current density for IMTJs is expressed by the following equations [31,32]: J c0 1⁄4 aceMst=ðlBgð0ÞÞ 1⁄2ðHex þ HdipÞ þ ðHki þ HdÞ ð1Þ”
Compact Modeling of Perpendicular-Anisotropy CoFeB/MgO Magnetic Tunnel Junctions (2012, background): “…the compilation speed of this model should be fast enough to ensure the transient simulation of very large scale integration circuits; consequently, some physical models such as the Landau–Lifshitz–Gilbert equation for the precessional motion of magnetization in the free layer [31] were discarded.”
Vertical-current-induced domain-wall motion in MgO-based magnetic tunnel junctions with low current densities (2011, background): “attribute the microscopic origin of DW displacements to the out-of-plane (‘field-like’) spin-transfer torqu”