Current-induced magnetization dynamics in current perpendicular to the plane spin valves

Covington, M.; AlHajDarwish, M.; Ding, Yunfei; Gokemeijer, N. J.; Seigler, Michael A.

doi:10.1103/physrevb.69.184406

Cited by 87 publications

(76 citation statements)

References 27 publications

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“…Charge shot noise in ferromagnetic spin valve devices has been discussed as well [4,5]. Interesting new questions have been raised by recent experimental studies on the dynamics of nano-scale spin valves [6,7,8] in which electric transport is affected by the magnetization direction of the ferromagnetic elements. Central to these studies is the spin-transfer torque exerted by a spin-polarized current on the magnetization causing it to precess or even reverse direction [9,10,11].…”

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“…Central to these studies is the spin-transfer torque exerted by a spin-polarized current on the magnetization causing it to precess or even reverse direction [9,10,11]. Covington et al [8] interpreted the observed dependence of noise spectra in nano-pillar spin valves on bias current direction in terms of this spin torque, but a full consensus has not yet been reached [12].…”

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Magnetization Noise in Magnetoelectronic Nanostructures

et al. 2005

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By scattering theory we show that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in the spin current is related to the increased Gilbert damping due to spin pumping, in accordance with the fluctuation-dissipation theorem. Spin current shot noise in the presence of an applied bias is the dominant contribution to the magnetization noise at low temperatures.PACS numbers: 72.25. Mk, 74.40.+k, 75.75.+a Time-dependent fluctuations of observables ("noise") are a nuisance for the engineer but also a fascinating subject of study for the physicist. The thermal current fluctuations in electric circuits as well as the Poissonian current fluctuations due to the discrete electron charge emitted by hot cathodes are classical textbook subjects. The fluctuations of the order parameter in ferromagnets, such as Barkhausen noise due to moving domain walls, have been studied by the magnetism community for almost a century. Recently, it has been discovered that electronic noise is dramatically modified in nanostructures. Theoretical predictions on the suppression of charge shot noise in quantum devices have been confirmed experimentally [1]. Spin current fluctuations, i.e., spin shot noise, is as yet a purely theoretical concept [2]. In nanoscale magnetism, thermal noise plays an important role by activating magnetization reversal of ferromagnetic clusters [3]. Charge shot noise in ferromagnetic spin valve devices has been discussed as well [4,5]. Interesting new questions have been raised by recent experimental studies on the dynamics of nano-scale spin valves [6,7,8] in which electric transport is affected by the magnetization direction of the ferromagnetic elements. Central to these studies is the spin-transfer torque exerted by a spin-polarized current on the magnetization causing it to precess or even reverse direction [9,10,11]. Covington et al. [8] interpreted the observed dependence of noise spectra in nano-pillar spin valves on bias current direction in terms of this spin torque, but a full consensus has not yet been reached [12].In a normal metal the average current of net spin angular momentum (spin current) vanishes but its fluctuations are finite. In this Letter we demonstrate that equilibrium and non-equilibrium spin current noise in normal metals is directly observable in hybrid ferromagnetnormal metal structures: The noise exerts a fluctuating spin-transfer torque on the magnetization vector causing an observable magnetization noise. The theory of noise in magnetoelectronic devices requires a consistent treatment of fluctuations in the currents as well as the magnetization. We demonstrate that thermal spin current fluctuations are instrumental for the spin pumping-enhanced Gilbert damping in magnetic multilayers [13] and that spin shot noise should be observable at low temperatures. The better understanding of noise in ferromagnetic spin valves should aid the development...

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Magnetization Noise in Magnetoelectronic Nanostructures

et al. 2005

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“…This ground breaking concept known as spin transfer, relies on the local interaction between a spin polarized current and the background magnetization of a ferromagnet. Spin transfer induced magnetization dynamics has been recently demonstrated experimentally in a wide variety of material systems and is rapidly reaching device maturity 3,4,5,6,7,8,9,10,11,12,13 . Furthermore, direct measurements of the magnetization dynamics 14,15,16 have shed light on the fundamental mechanism of spin transfer.…”

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Current-induced switching in single ferromagenetic layer nanopillar junctions

Özyilmaz

Kent

2006

Applied Physics Letters

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Current induced magnetization dynamics in asymmetric Cu/Co/Cu single magnetic layer nanopillars has been studied experimentally at room temperature and in low magnetic fields applied perpendicular to the thin film plane. In sub-100 nm junctions produced using a nanostencil process a bistable state with two distinct resistance values is observed. Current sweeps at fixed applied fields reveal hysteretic and abrupt transitions between these two resistance states. The current induced resistance change is 0.5%, a factor of 5 greater than the anisotropic magnetoresistance (AMR) effect. We present an experimentally obtained low field phase diagram of current induced magnetization dynamics in single ferromagnetic layer pillar junctions. 75.60.Jk, 75.30.Ds, 75.75.1a

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“…In order to technologically replace VCOs, STNOs should be able to deliver high microwave power outputs and must possess higher conversion efficiencies with a good quality factor. There have been consistent efforts [9][10][11] to improve the performance of STNOs based on typical trilayer magnetic tunnel junctions (MTJ). Various improvements proposed are centered around modifying the magnetic properties of the ferromagnet (FM).…”

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Resonant Spin-Transfer-Torque Nano-Oscillators

2017

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Spin transfer torque nano-oscillators are potential candidates for replacing the traditional inductor based voltage controlled oscillators in modern communication devices. Typical oscillator designs are based on trilayer magnetic tunnel junctions which are disadvantaged by low power outputs and poor conversion efficiencies. In this letter, we theoretically propose to use resonant spin filtering in pentalayer magnetic tunnel junctions as a possible route to alleviate these issues and present device designs geared toward a high microwave output power and an efficient conversion of the d.c. input power. We attribute these robust qualities to the resulting non-trivial spin current profiles and the ultra high tunnel magnetoresistance, both arising from resonant spin filtering. The device designs are based on the nonequilibrium Green's function spin transport formalism self-consistently coupled with the stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's equation. We demonstrate that the proposed structures facilitate oscillator designs featuring a large enhancement in microwave power of around 775% and an efficiency enhancement of over 1300% in comparison with typical trilayer designs. We also rationalize the optimum operating regions via an analysis of the dynamic and static device resistances. This work sets stage for pentalyer spin transfer torque nano-oscillator device designs that extenuate most of the issues faced by the typical trilayer designs.Spin transfer torque nano-oscillators (STNOs) are a class of non-linear nanoscale oscillators which have attracted a lot of interest from the physics as well as the applications perspective. The interest from the physics perspective stems from the need to advance the understanding of magnetization dynamics in nonlinear systems [1][2][3][4][5] . From the applications perspective, these devices find suitability in the modern communication electronics 6-8 . STNOs have better in-built features over traditionally used voltage control oscillators (VCOs), such as smaller size, lower cost and easier integrability to silicon technology. In order to technologically replace VCOs, STNOs should be able to deliver high microwave power outputs and must possess higher conversion efficiencies with a good quality factor. There have been consistent efforts 9-11 to improve the performance of STNOs based on typical trilayer magnetic tunnel junctions (MTJ). Various improvements proposed are centered around modifying the magnetic properties of the ferromagnet (FM). However, they have not been able to deliver microwave power outputs in excess of 0.3µW 11 . In this work we propose pentalayer device designs that make use of resonant spin filtering, termed as resonant tunneling magnetic tunnel junction (RTMTJ) structures, to circumvent these issues faced by typical trilayer based STNO designs. We demonstrate that owing to the novel spin-filtering physics in the proposed structures 12,13 , the resulting non-trivial spin current profiles and the high tunnel magneto resistanc...

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Current-induced magnetization dynamics in current perpendicular to the plane spin valves

Cited by 87 publications

References 27 publications

Magnetization Noise in Magnetoelectronic Nanostructures

Magnetization Noise in Magnetoelectronic Nanostructures

Current-induced switching in single ferromagenetic layer nanopillar junctions

Resonant Spin-Transfer-Torque Nano-Oscillators

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