Resonant Spin-Transfer-Torque Nano-Oscillators

Abstract

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...

Band-pass Fabry-Pèrot magnetic tunnel junctions

“…The MTJ structure has attracted a lot of attention due to the possibility of engineering a large tunnel magneto-resistance (TMR ≈ 200%) 3 and the current driven magnetization switching via the spintransfer torque (STT) effect [4][5][6][7] . Trilayer MTJs find their potential applications in magnetic field sensors 8,9 , STTmagnetic random access memories 10 and spin torque nano-oscillators (STNO) 11,12 . The MTJ performance for the aforesaid applications relies on large device TMR and low switching bias 9,12,13 .…”

“…Trilayer MTJs find their potential applications in magnetic field sensors 8,9 , STTmagnetic random access memories 10 and spin torque nano-oscillators (STNO) 11,12 . The MTJ performance for the aforesaid applications relies on large device TMR and low switching bias 9,12,13 . There have been consistent efforts in terms of materials development [14][15][16] and the device structure designs [17][18][19] to enhance the TMR and STT in magnetic tunnel junctions.…”

Terahertz spin-transfer torque oscillator based on a synthetic antiferromagnet

“…[4,5], hindering size shrinking down and consequently, many potential applications. However, fabricated by microscale or nanoscale technologies, spin transfer torque (STT) oscillator could shrink down to micrometer or sub-micrometer size [6][7][8].…”

Proposal for a solid-state magnetoresistive Larmor quantum clock

“…We further analyze the resulting interpretations of the tunneling time and the measurement back action in the presence of phase breaking effects [27,[30][31][32][33][34][35][36][37], that are intrinsic to solid state systems. We uncover that, while the time-keeping aspect of the Larmor clock is reasonably undeterred due to momentum and phase relaxation processes, it degrades significantly in the presence of spindephasing.…”

“…Typical interactions of this kind include pure phase relaxation via electronelectron interactions, momentum and phase relaxation via fluctuating local non-magnetic impurities, and spin relaxation via magnetic impurities. These aspects can be added phenomenologically within the framework of Keldysh NEGF formalism [27,[30][31][32][35][36][37] via appropriate dephasing self-energies.…”