Erratum: Basic principles of STT-MRAM cell operation in memory arrays

Khvalkovskiy, A. V.; Apalkov, Dmytro; Watts, Steven; Chepulskii, Roman V.; Beach, R. S.; Ong, A.; Tang, X.; Driskill-Smith, A.; Butler, W. H.; Visscher, P. B.; Chen, E; Nikitin, V.; Krounbi, M.

doi:10.1088/0022-3727/46/13/139601

Cited by 85 publications

(103 citation statements)

References 97 publications

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“…In ref. 3,11 , this energy is written 4 A ex K disk eff d t mag where A ex is the exchange stiffness and K disk eff the effective anisotropy of the disk. These expressions assume that the disk is larger than the domain wall i.e.…”

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confidence: 99%

Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions

Bouquin

Rao

Kar

et al. 2018

Applied Physics Letters

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We simulate the spin torque-induced reversal of the magnetization in thin disks with perpendicular anisotropy at zero temperature. Disks typically smaller than 20 nm in diameter exhibit coherent reversal. A domain wall is involved in larger disks. We derive the critical diameter of this transition. Using a proper definition of the critical voltage, a macrospin model can account perfectly for the reversal dynamics when the reversal is coherent. The same critical voltage appears to match with the micromagnetics switching voltage regardless of the switching path.Magnetization reversal in small particles is a long standing problem 1,2 that was recently put in a new context by the emergence of spin transfer torque (STT) magnetic random access memories 3 (MRAM). This technology is based on the STT-induced manipulation of the magnetization of nano-sized ultrathin disks with perpendicular magnetic anisotropy (PMA). In addition to its fundamental interest, the switching dynamics is of paramount application importance as it determines many of the performance metrics of this technology. Unfortunately experimental investigations are scarce 4-10 probably because of the technical difficulties associated with the small dimensions as well as the large frequencies involved in the switching process. As a result the switching paths are often conjectured from reasonnable but approximate models 11,12 , if not from overly simplified models like the macrospin picture 13-15 whose range of validity is still to establish.Here we unravel the size dependence of the switching dynamics by taking advantage of the accurary of micromagnetics. We first clarify how to implement STT in a way that is adequate for magnetic tunnel junctions (MTJ). We then describe the main switching regimes: coherent for small disks versus domain wall (DW) based at larger diameters. We discuss the critical diameter that separates these two regimes. We then parametrize the macrospin model to account exactly for the coherent regime. Finally we describe the size dependence of the switching voltage and provide a model valid whatever the switching mode. Our results clarify the predictive capability of the corpus of theories based on the macrospin model and therefore it has strong implications for magnetic random access memories.We are interested by the response of PMA disks to the STT associated with voltage steps applied through a tunnel junction. A first difficulty arises from the fact that the STT is most often expressed in units of current densities 18,19 while the applied voltage is a more correct metric in a tunnel junction context. Indeed the insulating nature of the tunnel oxide renders the voltage laterally a) Electronic mail: paul.bouquin@u-psud.fr uniform across the disk, while the current density is not. To implement STT within micromagnetics, we start from the Landau-Lifshitz-Gilbert-Slonczewski equation:where m is the normalised magnetization, γ the gyromagnetic ratio, H eff the effective field, and α the damping constant. We consider a spin polarization alon...

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confidence: 99%

Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions

Bouquin

Rao

Kar

et al. 2018

Applied Physics Letters

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“…In the p-MTJ spin-valve (stack A), the MgO tunneling barrier exhibited a combined layer of fcc (100) crystals (i in Figure 3a) and an amorphous layer (ii in Figure 3a), and both the Co 2 Fe 6 B 2 free and pinned layers were revealed to be amorphous layers (iii and iv in Figure 3a), thereby remarkably reducing the Δ1 coherent tunneling of the MgO tunneling barrier, which in turn greatly decreased the TMR ratio of the p-MTJ spin-valves. 34 In contrast, in the p-MTJ spin-valve (stack B), the MgO tunneling barrier showed an almost complete fcc (100)-crystalized layer (i in Figure 3b). In addition, the Co 2 Fe 6 B 2 free layer appeared as a locally body-centered-cubic-crystalized layer (ii in Figure 3b), whereas the Co 2 Fe 6 B 2 pinned layer appeared as an almost amorphous layer (iii in Figure 3b).…”

Section: Resultsmentioning

confidence: 93%

Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer

2016

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Recently, p-MTJ spin-valves with top Co 2 Fe 6 B 2 free layers have been widely studied. They potentially experience crystallinity degradation in the face-centered-cubic (fcc) structure of the MgO tunneling barrier as a result of the diffusion of Ta atoms and a significant amount of Fe atoms from the Co 2 Fe 6 B 2 free and pinned layers. A new design of the p-MTJ spin-valve using a nanoscale-thick W bridging and capping layer demonstrated the absence of significant crystallinity degradation in the fcc structure and showed a limited diffusion of Fe atoms, thus achieving a TMR ratio of~143% at an ex-situ annealing temperature of 400°C.

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“…Such films are used for decades in mass storage technologies, both as medium and in read-out devices [10]. The emerging applications of such films in electronics include spinbased computing [11] and very high density magnetic RAM-type memories [12,13]. For several years now there is growing interest in utilizing magnetic domain walls (DWs) in patterned and continuous thin films, both in electronics and biochemistry.…”

Section: Introductionmentioning

confidence: 99%

Magnetic domain propagation in Pt/Co/Pt micro wires with engineered coercivity gradients along and across the wire

Jarosz

Gaul

Urbaniak

et al. 2017

Journal of Magnetism and Magnetic Materials

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Erratum: Basic principles of STT-MRAM cell operation in memory arrays

Cited by 85 publications

References 97 publications

Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions

Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions

Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer

Magnetic domain propagation in Pt/Co/Pt micro wires with engineered coercivity gradients along and across the wire

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