First-principles study of magnetization relaxation enhancement and spin transfer in thin magnetic films

Zwierzycki, M.; Tserkovnyak, Yaroslav; Kelly, Paul J.; Brataas, Arne; Bauer, G.

doi:10.1103/physrevb.71.064420

Cited by 224 publications

(251 citation statements)

References 44 publications

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“…Both band structure and disorder effects can be taken into account by first-principles electronicstructure calculation as demonstrated for metallic structures. 26 Recently, a magnetization-induced electrical voltage of the order of V was measured for an FIN structure by Moriyama et al 27 The authors explain their findings by spin pumping, but note that the signal is larger than expected. An FMR generated electric voltage generation up to 100 V was theoretically predicted for such FIN structures.…”

Section: ͑6͒mentioning

confidence: 99%

Charge pumping in magnetic tunnel junctions: Scattering theory

2008

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We study theoretically the charge transport pumped by magnetization dynamics through epitaxial FIF and FNIF magnetic tunnel junctions ͑F, ferromagnet; I, insulator; N, normal metal͒. We predict a small but measurable dc pumping voltage under ferromagnetic resonance conditions for collinear magnetization configurations, which may change sign as a function of barrier parameters. A much larger ac pumping voltage is expected when the magnetizations are at right angles. Quantum size effects are predicted for an FNIF structure as a function of the normal layer thickness. DOI: 10.1103/PhysRevB.77.180407 PACS number͑s͒: 85.75.Ϫd, 72.25.Ϫb, 73.40.Gk A magnetic tunnel junction ͑MTJ͒ consists of a thin insulating tunnel barrier ͑I͒ that separates two ferromagnetic conducting layers ͑F͒ with variable magnetization direction. 1 With a thin normal metal layer inserted next to the barrier, the MTJ is the only magnetoelectronic structure in which quantum size effects on electron transport have been detected experimentally. 2 More importantly, MTJs based on transition-metal alloys and epitaxial MgO barriers 3,4 are the core elements of the magnetic random-access memory ͑MRAM͒ devices 5 that are operated by the current-induced spin-transfer torque. 6,7 It is known that a moving magnetization of a ferromagnet pumps a spin current into an attached conductor. 8 Spin pumping can be observed indirectly as increased broadening of ferromagnetic resonance ͑FMR͒ spectra. 9 The spin accumulation created by spin pumping can be converted into a voltage signal by an analyzing ferromagnetic contact. 10 This process can be divided into two steps: ͑i͒ the dynamical magnetization pumps out a spin current with zero net charge current, ͑ii͒ the static magnetization ͑of the analyzing layer͒ filters the pumped spin current and gives a charge current. In the presence of spin-flip scattering, the spin-pumping magnet can generate a voltage even in an FN bilayer. 11,12 Spinpumping by a time-dependent bulk magnetization texture such as a moving domain wall is also transformed into an electromotive force. 13 Other experiments on spin-pumping induced voltages have also been reported. 14,15 Here we present a model study of spin-pumping induced voltages ͑charge pumping͒ in MTJs. Since the ferromagnets are separated by tunnel barrier, we cannot use the semiclassical approximations appropriate for metallic structures. 10,11,16,17 Instead, we present a full quantum-mechanical treatment of the currents in the tunnel barrier by scattering theory. The high quality of MgO tunnel junctions and the prominence of quantum oscillations observed in FNIF structures ͑even for alumina barriers͒ provide the motivation to concentrate on ballistic structures in which the transverse Bloch vector is conserved during transport. For a typical MTJ under FMR with cone angle = 5°at frequency f = 20 GHz, we find a dc pumping voltage of ͉V cp ͉ Ӎ20 nV for collinear magnetization configurations or ac voltage with amplitude Ṽ cp Ӎ 0.25 V for perpendicular configurations. The magnetiza...

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Section: ͑6͒mentioning

confidence: 99%

Charge pumping in magnetic tunnel junctions: Scattering theory

2008

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“…29 The mixing conductance is most easily calculated in terms of the reflection matrices. 43,53 We consider here interfaces in diffuse metallic systems which implies that we have to use a generalization of the Schep correction 25,31 by replacing the bare G ␣␤ ͑⑀͒ −1…”

Section: Magneto-peltier and Magnetothermopower In Spin Valvesmentioning

confidence: 99%

Thermoelectric effects in magnetic nanostructures

et al. 2009

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We model and evaluate the Peltier and Seebeck effects in magnetic multilayer nanostructures by a finiteelement theory of thermoelectric properties. We present analytical expressions for the thermopower and the current-induced temperature changes due to Peltier cooling/heating. The thermopower of a magnetic element is in general spin polarized, leading to spin-heat coupling effects. Thermoelectric effects in spin valves depend on the relative alignment of the magnetization directions and are sensitive to spin-flip scattering as well as inelastic collisions in the normal-metal spacer.

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“…Generally, the mixing conductance has a real and an imaginary part, which couple to the in-plane and out-of-plane terms in the dynamics respectively. Although the outof-plane spin transfer torque is important in magnetic tunnel junctions [45][46][47][48][49][50][51][52][53], it is negligible in fully metallic multilayers [54,55]. Thus we neglect Im(G  ) and the associated out-of-plane spin transfer torque.…”

Section: Modeling Schemementioning

confidence: 99%

Self-consistent calculation of spin transport and magnetization dynamics

et al. 2013

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A spin-polarized current transfers its spin-angular momentum to a local magnetization, exciting various types of current-induced magnetization dynamics. So far, most studies in this field have focused on the direct effect of spin transport on magnetization dynamics, but ignored the feedback from the magnetization dynamics to the spin transport and back to the magnetization dynamics. Although the feedback is usually weak, there are situations when it can play an important role in the dynamics. In such situations, simultaneous, self-consistent calculations of the magnetization dynamics and the spin transport can accurately describe the feedback. This review describes in detail the feedback mechanisms, and presents recent progress in self-consistent calculations of the coupled dynamics. We pay special attention to three representative examples, where the feedback generates non-local effective interactions for the magnetization after the spin accumulation has been integrated out. Possibly the most dramatic feedback example is the dynamic instability in magnetic nanopillars with a single magnetic layer. This instability does not occur without non-local feedback. We demonstrate that full self-consistent calculations generate simulation results in much better agreement with experiments than previous calculations that addressed the feedback effect approximately.The next example is for more typical spin valve nanopillars. Although the effect of feedback is less dramatic because even without feedback the current can make stationary states unstable and induce magnetization oscillation, the feedback can still have important consequences. For instance, we show that the feedback can reduce the linewidth of oscillations, in agreement with experimental observations. A key aspect of this reduction is the suppression of the excitation of short wave length spin waves by the non-local feedback.Finally, we consider nonadiabatic electron transport in narrow domain walls. The non-local feedback in these systems leads to a significant renormalization of the effective nonadiabatic 3 spin transfer torque. These examples show that the self-consistent treatment of spin transport and magnetization dynamics is important for understanding the physics of the coupled dynamics and for providing a bridge between the ongoing research fields of current-induced magnetization dynamics and the newly emerging fields of magnetization-dynamics-induced generation of charge and spin currents.

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First-principles study of magnetization relaxation enhancement and spin transfer in thin magnetic films

Cited by 224 publications

References 44 publications

Charge pumping in magnetic tunnel junctions: Scattering theory

Charge pumping in magnetic tunnel junctions: Scattering theory

Thermoelectric effects in magnetic nanostructures

Self-consistent calculation of spin transport and magnetization dynamics

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