Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions

Timopheev, A. A.; Sousa, R. C.; Chshiev, M.; Buda-Prejbeanu, L. D.; Diény, B.

doi:10.1103/physrevb.92.104430

Cited by 36 publications

(26 citation statements)

References 51 publications

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“…We emphasize this point, because the state diagram of Fig. 3(a) with linear and parallel switching frontiers is sometimes interpreted as an indication of macrospin behavior 10 .…”

Section: Discussionmentioning

confidence: 98%

Size dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions

Devolder

Goff

Nikitin³

2016

Phys. Rev. B

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We have time-resolved the spin-transfer-torque (STT)-induced switching in perpendicularly magnetized tunnel junctions (pMTJ) of diameters from 50 to 250 nm in the sub-threshold thermally activated regime. When the field and the spin-torque concur to both favor the P to AP transition, the reversal yields monotonic resistance ramps that can be interpreted as a domain wall propagation through the device at velocities of the order of 17 to 30 nm/ns; smaller cells switch faster, and proportionnally to their diameter. At the largest sizes, transient domain wall pinning can occasionally occur. When the field hinders the P to AP transition triggered by the spin-torque, the P to AP switching is preceded by repetitive switching attempts, during which the resistance transiently increases until successful reversal occurs. At 50 nm, the P to AP switching proceeds reproducibly in 3 ns, with a monotonic featureless increase of the device resistance. In the reverse transition (AP to P), the variability of thermally activated reversal is not restricted to stochastic variations of incubation delays before the onset of reversal: several reversal paths are possible even in the smallest perpendicularly magnetized junctions. Besides, the non uniform nature of the magnetic response seems still present at the nanoscale, with sometimes electrical signatures of strong disorder during the AP to P reversal. The AP to P transition is preceded by a strong instability of the AP states in devices larger than 100 nm. The resistance becomes extremely agitated before switching to P in a path yielding a slow (20 to 50 ns) and irregular increase of the conductance with substantial event-to-event variability. Unreversed bubbles of typical diameter 60 nm can persist a few additional microseconds in the largest junctions. The complexity of the AP to P switching is reduced but not suppressed when the junctions are downsized below 60 nm. The instability of the initial AP state is no longer detected but the other features are maintained. In the smallest junctions (50 nm) we occasionally observe much faster (sub-1 ns) AP to P switching events that could result from a macrospin process. We discuss the origin of the switching asymmetry and the size dependence, with an emphasis on the role of the non uniformities of the stray field emanating from the reference layers of the tunnel junction, which affects the zones in which nucleation is favored.The spin-transfer-torque (STT) manipulation of the magnetization in magnetic tunnel junctions (MTJ) is a very active research field, because the interplay between magnetizationdependent transport properties 1 and the spin torques results in a rich variety of phenomena 2 . Perpendicular Magnetic Anisotropy (PMA) systems are an ideal playground to explore STT-induced dynamics 3,4 , because the high symmetry of their magnetic properties matches with the symmetries of the physical system when the nanomagnets are shaped to circular disks. Besides, high quality PMA MTJs can now be found 5-7 , as they were optimized owing to ...

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“…We emphasize this point, because the state diagram of Fig. 3(a) with linear and parallel switching frontiers is sometimes interpreted as an indication of macrospin behavior 10 .…”

Section: Discussionmentioning

confidence: 98%

Size dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions

Devolder

Goff

Nikitin³

2016

Phys. Rev. B

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“…The procedure for VH stability diagram measurements is similar to that described in Ref. [20]. A single pMTJ pillar was wire bonded and placed in a physical properties measurement system (PPMS) on a sample rotator.…”

Section: Experimental Stability Diagramsmentioning

confidence: 99%

“…In this work, instead of measuring the device resistance-magnetic field (R-H) loops at constant writing pulse amplitude, as in Ref. [20], we measured a device resistance-writing pulse voltage (R-V) loops at each magnetic field point. Within each R-V loop, a sequence of writing pulses with continuously changing amplitude was applied and after each writing pulse the resistance of the pMTJ pillar was measured by applying a small bias current (∼1 µA).…”

Section: Experimental Stability Diagramsmentioning

confidence: 99%

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Stability phase diagram of a perpendicular magnetic tunnel junction in noncollinear geometry

et al. 2017

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International audienceExperimental measurements performed on MgO-based perpendicular magnetic tunnel junctions show a strong dependence of the stability voltage-field diagrams as a function of the direction of the magnetic field with respect to the plane of the sample. When the magnetic field is applied in-plane, systematic nonlinear phase boundaries are observed for various lateral sizes. The simulation results based on the phenomenological Landau-Lifshitz-Gilbert equation including the in-plane and out-of-plane spin transfer torques are consistent with the measurements if a second-order anisotropy contribution is considered. Furthermore, performing the stability analysis in linear approximation allowed us to analytically extract the critical switching voltage at zero temperature in the presence of an in-plane field. This study indicates that in the noncollinear geometry investigations are suitable to detect the presence of the second-order term in the anisotropy. Such higher order anisotropy term can yield an easy-cone anisotropy which reduces the thermal stability factor but allows for more reproducible spin transfer torque switching due to a reduced stochasticity of the switching. As a result, the energy per write event decreases much faster than the thermal stability factor as the second-order anisotropy becomes more negative. Easy-cone anisotropy can be useful for fast-switching spin transfer torque magnetic random access memories provided the thermal stability can be maintained above the required value for a given memory specification

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“…Smaller values of attempt time are also sometimes reported, for example τ 0 = 0.1 ns. 17 Increasing (decreasing) the value of τ 0 to 10 ns (0.1 ns) would increase (decrease) the value of n needed to match the simulated data by ∼ 5%. Since typical values of τ 0 are 0.1 ns to 1 ns, this cannot be used to adjust the value of n to be equal to 2.…”

Section: Resultsmentioning

confidence: 99%

Estimation of thermal stability factor and intrinsic switching current from switching distributions in spin-transfer-torque devices with out-of-plane magnetic anisotropy

Heindl

Chaudhry²,

Russek

2018

AIP Advances

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We performed macromagnetic simulations of switching statistics in spin-transfer-torque devices with out-of-plane magnetic anisotropy and thermal stability factors ranging from Δ = 21 to Δ = 279. We compared our results of the simulated switching probabilities in low-currents (read-disturb) and long-times (thermally activated) limits with the predictions of several existing models that predict the switching probability to be proportional to (1 − I/Ic0)n (Eq. 3), with exponent n varying from n = 1 to n = 2.2. We found that the best match to the simulated data in these two limits is obtained with values of n ≈ 1.76, when currents are limited to ∼ 0.6-0.8 Ic0.

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Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions

Cited by 36 publications

References 51 publications

Size dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions

Size dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions

Stability phase diagram of a perpendicular magnetic tunnel junction in noncollinear geometry

Estimation of thermal stability factor and intrinsic switching current from switching distributions in spin-transfer-torque devices with out-of-plane magnetic anisotropy

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