Thermal relaxation rates of magnetic nanoparticles in the presence of magnetic fields and spin-transfer effects

Rippard, William H.; Heindl, R. A.; Pufall, Matthew R.; Russek, Stephen E.; Kos, Anthony B.

doi:10.1103/physrevb.84.064439

Cited by 59 publications

(48 citation statements)

References 37 publications

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“…They can be used to generate random bits at kHz frequencies, sufficient for real-time brain-inspired systems like 7 , but not for high performance applications. In our 50 × 150nm superparamagnetic tunnel junctions, we identified that the switching occurs through nucleation and propagation of a magnetic domain, probably seeded by fluctuations in a subset of grains within it 31 (supplementary information S3). By contrast, recent experiments on perpendicular magnetic anisotropy (PMA) magnetic tunnel junctions have shown that aggressively scaled devices (diameters smaller than 35nm) switch at the scale of the whole volume 34 .…”

Section: Scaling Capabilities Of the Random Number Generators In mentioning

confidence: 99%

“…Unlike the case of MRAMs, for which the magnetization direction of the free magnet is highly stable and can only be switched by proper external action, the magnetization direction of the superparamagnetic free magnet spontaneously switches between its two stable states, due to low stability relative to thermal fluctuations ( Fig. 1(c)) 31,32 . Here, no bias or perturb scheme is required to provoke these random fluctuations, but only temperature.…”

Section: Exploiting the Stochastic Behavior Of Superparamagnetic mentioning

confidence: 99%

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Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

et al. 2017

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Low-energy random number generation is critical for many emerging computing schemes proposed to complement or replace von Neumann architectures. However, current random number generators are always associated with an energy cost that is prohibitive for these computing schemes. In this paper, we introduce random number bit generation based on specific nanodevices: superparamagnetic tunnel junctions. We experimentally demonstrate high quality random bit generation that represents orders-of-magnitude improvements in energy efficiency compared to current solutions. We show that the random generation speed improves with nanodevice scaling, and investigate the impact of temperature, magnetic field and crosstalk. Finally, we show how alternative computing schemes can be implemented using superparamagentic tunnel junctions as random number generators. These results open the way for fabricating efficient hardware computing devices leveraging stochasticity, and highlight a novel use for emerging nanodevices.

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Section: Scaling Capabilities Of the Random Number Generators In mentioning

confidence: 99%

Section: Exploiting the Stochastic Behavior Of Superparamagnetic mentioning

confidence: 99%

Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

et al. 2017

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“…3 The temperature dependence of  can be understood via the by several orders of magnitude concurring with experimental results. 11 The virtue of our numerically exact solutions of the recurrence relations for the relevant statistical moments is that they hold for the most comprehensive formulation of the generic nanopillar model ( Fig. 1), i.e., for arbitrary directions of the external field and spin polarization and for arbitrary free energy density, yielding the STT switching characteristics under conditions otherwise inaccessible.…”

Section: Vresultsmentioning

confidence: 88%

“…8 Such effects underpin the relatively new subject of spintronics, 9 where the carrier of information is the spin state of a ferromagnetic material. Typical practical applications include very-high-speed current-induced magnetization switching by (a) reversing the orientation of magnetic bits in high density memory structures as opposed to the more conventional Oersted field switching 7,10,11 and (b) using spin polarized currents both to generate and manipulate steady state microwave oscillations with a frequency proportional to the spin-polarization current 12,13 via the steady state magnetization precession. Essentially both objectives (a) and (b) can be achieved because, depending on its sign, the spin current either enhances or diminishes the effective damping representing the microscopic degrees of freedom of a ferromagnetic film 8 (cf.…”

Section: Introductionmentioning

confidence: 99%

Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments

et al. 2013

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Thermal fluctuations of nanomagnets driven by spin-polarized currents are treated via the Landau-Lifshitz-Gilbert equation generalized to include both the random thermal noise field and the Slonczewski spin-transfer torque term. By averaging this stochastic (Langevin) equation over its realizations, the explicit infinite hierarchy of differential-recurrence relations for statistical moments (averaged spherical harmonics) is derived for arbitrary demagnetizing factors and magnetocrystalline anisotropy for the generic nanopillar model of a spin-torque device comprising two ferromagnetic strata representing the free and fixed layers and a nonmagnetic conducting spacer all sandwiched between two ohmic contacts. The influence of thermal fluctuations and spin-transfer torques on relevant switching characteristics, such as the stationary magnetization, the magnetization reversal time, etc., is calculated by solving the hierarchy for wide ranges of temperature, damping, external magnetic field, and spinpolarized current indicating new spin-torque effects in the thermally assisted magnetization reversal comprising several orders of magnitude. In particular, a pronounced dependence of the switching characteristics on the directions of the external magnetic field and the spin polarization exists.

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“…In the presence of an external magnetic field without any read disturb current [26,27], Eq. (2) transforms to…”

Section: Sttram Retention Enhancementmentioning

confidence: 99%

Replacing eFlash with STTRAM in IoTs: Security Challenges and Solutions

Khan

Park

et al. 2017

J Hardw Syst Secur

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Spin-transfer torque RAM (STTRAM) is an emerging non-volatile memory (NVM) technology that provides better endurance, write energy and performance than traditional NVM technologies such as Flash. In embedded application such as microcontroller SoC of Internet of Things (IoTs), embedded Flash (eFlash) is widely employed. However, eFlash is also associated with cost, poor reliability and high write energy consumption. Therefore, replacing eFlash with emerging NVMs is desirable in IoTs and have been investigated in literature. Although promising, STTRAM brings several new security and privacy challenges such as magnetic attacks that pose a significant threat to sensitive program stored in memory. In this paper, we investigate these challenges and propose a novel memory architecture for attack resilient IoT network. The information redundancy present in a homogeneous peer-to-peer connected IoT network is exploited to restore the corrupted memory of any IoT node after magnetic attack. Since restoring program memory from other IoT is associated with energy overhead, we propose to reduce the number of corrupted bits by using high retention STTRAM at the cost of one-time write energy overhead. Energy overhead for the recovery process is estimated using commercial IoT boards, showing 19.85 nJ/bit for 100 MB data transfer. Increasing the STTRAM resiliency with a thermal stability factor of 72 reduces the recovery energy overhead to 9.01 nJ/bit (54.61% improvement) for a 100 Oe magnetic attack persisting for 1 s. We further propose to reduce the transfer energy by applying error correction codes (ECC) in STTRAM, which shows 10× (10 5 ×) improvement in energy for 64 (128) bit words with 16-bit ECC.

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Thermal relaxation rates of magnetic nanoparticles in the presence of magnetic fields and spin-transfer effects

Cited by 59 publications

References 37 publications

Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments

Replacing eFlash with STTRAM in IoTs: Security Challenges and Solutions

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