Binary switching in a ‘symmetric’ potential landscape

Roy, Kaustuv; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

doi:10.1038/srep03038

Cited by 91 publications

(137 citation statements)

References 45 publications

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“…In the first step, the magnetization rotates from the initial stable orientation along the major axis by an acute angle. In the second step, the magnetization rotates by an additional angle, bringing it closer to the other stable direction, and finally when the stresses are withdrawn, the magnetization settles into the other stable direction, completing a 180 o rotation 1 .There are other proposed methods of implementing 180 o rotation with strain, but they either require very precise timing of the stress cycle which is nearly impossible in the presence of thermal noise at room temperature 37,38 , or special material properties 39 . In contrast, the two step method does not call for extreme precision, is practical and error-resilient, and works with any magnetostrictive material, whether crystalline, poly-crystalline or amorphous.…”

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confidence: 99%

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

et al. 2017

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Rotating the magnetization of a shape anisotropic magnetostrictive nanomagnet with voltagegenerated stress/strain dissipates much less energy than most other magnetization rotation schemes, but its application to writing bits in non-volatile magnetic memory has been hindered by the fundamental inability of stress/strain to rotate magnetization by full 180 o . Normally, stress/strain can rotate the magnetization of a shape anisotropic elliptical nanomagnet by only up to 90 o , resulting in incomplete magnetization reversal. Recently, we predicted that applying uniaxial stress sequentially along two different axes that are not collinear with the major or minor axis of the elliptical nanomagnet will rotate the magnetization by full 180 o [1]. Here, we demonstrate this complete 180 o rotation in elliptical Co-nanomagnets (fabricated on a piezoelectric substrate) at room temperature. The two stresses are generated by sequentially applying voltages to two pairs of shorted electrodes placed on the substrate such that the line joining the centers of the electrodes in one pair intersects the major axis of a nanomagnet at ~+30 o and the line joining the centers of the electrodes in the other pair intersects at ~ -30 o . A finite element analysis has been performed to determine the stress distribution underneath the nanomagnets when one or both pairs of electrodes are activated, and this has been approximately incorporated into a micromagnetic simulation of magnetization dynamics to confirm that the generated stress can produce the observed magnetization rotations. This result portends an extremely energy-efficient non-volatile "straintronic" memory technology predicated on writing bits in nanomagnets with electrically generated stress.Nanomagnets are the bedrock of non-volatile memory. A magnetic random access memory (MRAM) cell is implemented with a magneto-tunneling junction (MTJ) consisting of two nanomagnetic layers, one hard and one soft, separated by a spacer (tunneling) layer. The soft layer is often shaped like an elliptical disc which, if sufficiently thick, has two in-plane stable magnetization directions pointing in opposite directions along the major axis of the ellipse. They encode and store the binary bits 0 and 1. The stored bit * Corresponding author. E-mail: sbandy@vcu.edu is "read" by measuring the resistance of the MTJ which has two discrete values depending on the two magnetization orientations of the soft layer, i.e., for the two bits 0 and 1. "Writing" of bits is accomplished by switching the magnetization of the soft layer between the two anti-parallel directions of stable magnetization (180 0 rotation of the magnetization) with an external agent.There are many strategies to rotate the magnetization of the soft layer. Popular approaches include passing a spin current through the soft layer to generate a spin transfer torque 2-7 or spin orbit torque [8][9][10][11] or domain wall motion [12][13] . Other approaches involve using voltage controlled magnetic anisotropy 14 , magnetoelectric effects 15-17 ...

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confidence: 99%

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

et al. 2017

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“…If the system, on the other hand, is nonlinear, the bound-state contributions become important, modifying the photon statistics of the output light as shown in the main text. In the limit of U → ∞, B's become exactly the same as those of the coupled two-level atoms [50]. Finally, we can find the two-photon scattering matrix from, as in [33],…”

Section: Two-photon Scatteringmentioning

confidence: 89%

Few-photon transport in many-body photonic systems: A scattering approach

et al. 2015

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We study the quantum transport of multi-photon Fock states in one-dimensional Bose-Hubbard lattices implemented in QED cavity arrays (QCAs). We propose an optical scheme to probe the underlying many-body states of the system by analyzing the properties of the transmitted light using scattering theory. To this end, we employ the Lippmann-Schwinger formalism within which an analytical form of the scattering matrix can be found. The latter is evaluated explicitly for the two particle/photon-two site case using which we study the resonance properties of two-photon scattering, as well as the scattering probabilities and the second-order intensity correlations of the transmitted light. The results indicate that the underlying structure of the many-body states of the model in question can be directly inferred from the physical properties of the transported photons in its QCA realization. We find that a fully-resonant two-photon scattering scenario allows a faithful characterization of the underlying many-body states, unlike in the coherent driving scenario usually employed in quantum Master equation treatments. The effects of losses in the cavities, as well as the incoming photons' pulse shapes and initial correlations are studied and analyzed. Our method is general and can be applied to probe the structure of any many-body bosonic models amenable to a QCA implementation including the Jaynes-Cummings-Hubbard, the extended Bose-Hubbard as well as a whole range of spin models.

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“…What makes it happen is the out-of-plane dynamics of the magnetization vector that generates a helpful torque to rotate the magnetization from 90 • to 180 • [85]. This out of plane dynamics, crucial for a complete bit flip or the 180 • rotation, is either absent or very weak in a pillar, making bit flip via stress nearly impossible.…”

Section: Other-spin-based Logic and Memorymentioning

confidence: 99%

“…The associated strain is transferred elastically to the magnetostrictive layer, generating stress in it and rotating its magnetization by large angles [76][77][78][79][80][81][82][83][84]. If the strain is withdrawn at the right juncture, rotation by ∼180 • is possible with >99.99% probability even in the presence of thermal noise at room temperature [85]. The switching takes less than 1 ns to complete, making this strategy one of the most energy efficient, and yet relatively fast, switching methodologies extant.…”

Section: Hybrid Spintronics and Straintronicsmentioning

confidence: 99%

Information Processing with Electron Spins

Bandyopadhyay

2012

ISRN Materials Science

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Information processors process information in a variety of ways. The human brain processes information through a highly interconnected system of neurons and synapses, while a digital computer processes information by having a binary switch toggle on and off in response to a stream of binary bits. The "switch" is the most primitive unit of the modern computer. The better it is (faster, more energy efficient, more reliable, etc.), the more advanced is the computer hardware. Energy efficiency, however, is more important than any other attribute, not so much because energy is costly, but because too much energy dissipation prevents increasing the density of switches on a chip that is necessary to make the chip increasingly more powerful. Reducing dissipation entails radically new and often revolutionary approaches for implementing the switch. One such approach is to encode digital bit information in the spin polarization of a single electron (or ensemble of electrons) and then using two mutually antiparallel polarizations to represent the binary bits 0 and 1. Switching between the bits can be accomplished by simply flipping the polarizations of the spins, which takes very little energy. Such switches are extremely energy efficient if designed properly, but they are somewhat slower than traditional transistor-based switches and can be more error prone. This paper discusses the pros and cons of spin-based switches and introduces the reader to the most recent advancements in information processing predicated on encoding information in electron spin polarization.

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Binary switching in a ‘symmetric’ potential landscape

Cited by 91 publications

References 45 publications

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

Few-photon transport in many-body photonic systems: A scattering approach

Information Processing with Electron Spins

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