Band-pass Fabry-Pèrot magnetic tunnel junctions

Abstract

We propose a high-performance magnetic tunnel junction by making electronic analogs of optical phenomena such as anti-reflections and Fabry-Pèrot resonances. The devices we propose feature anti-reflection enabled superlattice heterostructures sandwiched between the fixed and the free ferromagnets of the magnetic tunnel junction structure. Our predictions are based on the non-equilibrium Green's function spin transport formalism coupled selfconsistently with the Landau-Lifshitz-Gilbert-Slonczewski equation. Owing to the physics of bandpass spin filtering in the bandpass superlattice magnetic tunnel junction device, we demonstrate an ultra-high boost in the tunnel magneto-resistance (TMR≈ 5 × 10 4 %) and nearly 92% suppression of spin transfer torque switching bias in comparison to a traditional trilayer magnetic tunnel junction device. The proof of concepts presented here can lead to next-generation spintronics device design harvesting the rich physics of superlattice heterostructures and exploiting spintronic analogs of optical phenomena.Spintronics involves the manipulation of the intrinsic spin along with the charge of electrons and has emerged as an active area of research with direct engineering applications for next-generation logic and memories. A hallmark device that leads the development of the technology is the trilayer magnetic tunnel junction (MTJ), which consists of two ferromagnets (FM) separated by an insulator such as MgO 1,2 . 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 4-7 . 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 . There have been consistent efforts in terms of materials development 14-16 and the device structure designs 17-19 to enhance the TMR and STT in magnetic tunnel junctions. When it comes to device structures, the double barrier MTJ has been extensively explored both theoretically and experimentally to achieve better TMR and switching characteristics 19,20 . Owing to the physics of resonant tunneling, the double barrier structure has been predicted to provide a high TMR ( ≈ 2500%) 9,12 and nearly 44% lower switching bias 19 in comparison with the trilayer MTJ device.The Fabry-Pèrot resonances in the electronic analog are realized by superlattice (SL) structures ( Fig. 1(a)) consisting of periodic stacks of two dissimilar materials with layer thicknesses of a few nanometers. SL structures have been explored extensively in the field of photonics, electronics and thermoelectronics 21,22 . In the area of spintronics, few studies 18,23 have explored SL structures made of alternate layers of an insulator and normal metal (NM) sandwiched between the two FMs as a route to enhance the TM...

Proposal for a solid-state magnetoresistive Larmor quantum clock

“…By means of an engineered pre-selection in one of the ferromagnetic contacts, we also elucidated how one can make the measurement "weak" by minimizing the back-action, while keeping the tunneling time unchanged. We then analyzed 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]intrinsic to solid state systems. It is clearly demonstrated 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.…”

“…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.…”

Optimally Sharp Energy Filtering of Quantum Particles via Homogeneous Planar Inclusions

“…It should be finally remarked that energy filtering plays a crucial role in nanostructured thermoelectric generators 30 , where the output power can be further boosted with help from Fabry-Perot cavities 31 or in coolers with increased coefficient of performance 32 . Similarly, response selectivity with respect to the impinging energy of the beams is important in the operation of magnetic tunnel junctions with band pass utilities 33 and quantum Hall setups 34 considering the electron-nuclear spin flip-flops in the parametric vicinity of interest.…”

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“…Magnetoresistance (MR) effect provides an important target for spin operation in ferromagnet/barrier/ferromagnet magnetic tunnel junctions (MTJs). High MR ratio exceeding 400% is obtained by applying a crystalline magnesium oxide (MgO) 3 – 5 and different barrier structures 6 – 8 . In recent studies, a novel material, graphene, has attracted considerable attention as a two-dimensional Dirac material in spintronics 9 , 10 .…”