Spin torque switching of perpendicular Ta∣CoFeB∣MgO-based magnetic tunnel junctions

Worledge, D. C.; Hu, G.; Abraham, David W.; Sun, J. Z.; Trouilloud, P. L.; Nowak, Janusz; Brown, S. L.; Gaidis, M. C.; O’Sullivan, E. J.; Robertazzi, R. P.

doi:10.1063/1.3536482

Cited by 660 publications

(407 citation statements)

References 14 publications

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“…Nevertheless, the switching appears well described by thermally overcoming a single energy barrier, whose height is related to an excited magnetic subvolume in the free layer element [16]. Standard measurements probing the effects of spin torques on switching-current-field state diagrams and measurements of the Stoner-Wohlfarth astroid-also appear to agree with the simple effective barrier model [6,[17][18][19].…”

Section: Introductionsupporting

confidence: 51%

Switching field distributions with spin transfer torques in perpendicularly magnetized spin-valve nanopillars

et al. 2014

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We present switching field distributions of spin-transfer-assisted magnetization reversal in perpendicularly magnetized Co/Ni multilayer spin-valve nanopillars at room temperature. Switching field measurements of the Co/Ni free layer of spin-valve nanopillars with a 50 nm × 300 nm ellipse cross section were conducted as a function of current. The validity of a model that assumes a spin-current-dependent effective barrier for thermally activated reversal is tested by measuring switching field distributions under applied direct currents. We show that the switching field distributions deviate significantly from the double exponential shape predicted by the effective barrier model, beginning at applied currents as low as half of the zero field critical current. Barrier heights extracted from switching field distributions for currents below this threshold are a monotonic function of the current. However, the thermally induced switching model breaks down for currents exceeding the critical threshold.

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Section: Introductionsupporting

confidence: 51%

Switching field distributions with spin transfer torques in perpendicularly magnetized spin-valve nanopillars

et al. 2014

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“…It thus becomes evident that for high switching efficiency, one has to decrease α while keeping TMR high. Magnetic tunnel junctions (MTJs) based on CoFeB/MgO systems are well known to provide high TMR [2] and have recently been shown to possess PMA, which is attributed to the CoFeB/MgO interface.[3] A Ta layer is usually placed adjacent to the CoFeB to induce the proper crystallization necessary for PMA and high TMR [4]. In Ta/CoFeB/MgO systems, however, spin pumping to the Ta increases α.…”

mentioning

confidence: 99%

“…[3] A Ta layer is usually placed adjacent to the CoFeB to induce the proper crystallization necessary for PMA and high TMR [4]. In Ta/CoFeB/MgO systems, however, spin pumping to the Ta increases α.…”

mentioning

confidence: 99%

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Sabino

Lim

Tran

2014

Appl. Phys. Express

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We show by vector network analyzer ferromagnetic resonance measurements that low Gilbert damping α, down to 0.006, can be achieved in perpendicularly magnetized MgO/CoFeB/MgO thin films with ultrathin insertions of Ta in the CoFeB layer. Although increasing the number of Ta insertions allows thicker CoFeB layers to remain perpendicular, the effective areal magnetic anisotropy does not improve with more insertions, which come with an increase in α.Perpendicular magnetic anisotropy (PMA) is the key to further downscaling of spin transfer torque magnetoresistive random memory devices, as it allows two key requirements to be satisfied: low critical current I c0 and high thermal stability ∆, the latter of which is proportional to the energy barrier E b between the two stable magnetic states. The spin torque switching efficiency, defined as E b /I c0 , is commonly used as a metric to account for both requirements. For a StonerWohlfarth model, it is given by [1] ( /4e) · (η/α), where α is the Gilbert damping parameter, and η is the spin polarization factor, which is related to the tunnel magnetoresistance ratio (TMR) by η = [TMR(TMR + 2)] 1/2 /[2(TMR + 1)]. It thus becomes evident that for high switching efficiency, one has to decrease α while keeping TMR high. Magnetic tunnel junctions (MTJs) based on CoFeB/MgO systems are well known to provide high TMR [2] and have recently been shown to possess PMA, which is attributed to the CoFeB/MgO interface.[3] A Ta layer is usually placed adjacent to the CoFeB to induce the proper crystallization necessary for PMA and high TMR [4]. In Ta/CoFeB/MgO systems, however, spin pumping to the Ta increases α.[5] Moreover, the CoFeB layer also needs to be ultrathin (typically less than 1.5nm) in order to exhibit PMA. [3] To improve the thermal stability as devices are scaled down to smaller diameters, increasing the effective areal anisotropy energy density K e f f t is desired.One approach to address these issues is the use of double-MgO structures, i.e., those in which both the barrier layer and capping layer straddling the free layer are made of MgO. Improved I c0 and/or ∆ have been reported in devices using double MgO free layers. [6,7,8,9] The improvement in thermal stability is attributed to the additional CoFeB/MgO interface, whereas lower I c0 is associated with low α. Indeed, α down to 0.005 has been measured in in-plane MgO/FeB/MgO films,[10] which agrees with device measurements.[11] The stacks investigated in these damping studies, however, did not have the Ta layer used in practical free layers with perpendicular anisotropy. [9,12] In addition, although the interfacial anisotropy in the out-of-plane devices measured by Tsunegi et al.[11] can be as high as 3.3 mJ/m 2 , the effective perpendicular anisotropy was rather low (K e f f t ≈ 0.04mJ/m 2 ) relative to that of a Ta/CoFeB/MgO stack [3]. In this work, we explore the influence of Ta insertions within the CoFeB layer of MgO/CoFeB/MgO films by magnetometry and vector network analyzer ferromagnetic resonance (VNA-...

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“…6,7 Nevertheless, recent experiments on TMs/FeCoB/MgO revealed evidence that the role of 5d or 4d orbitals is more decisive; in other words, that the 5d (4d) TMs/CoFeB interface is the origin of the observed PMCA. 8,9 On the other hand, the magnetism in multilayers of 4d and 5d TMs grown on body-centered cubic (bcc) Fe substrate has been a long-standing subject of both experiment [10][11][12][13][14][15] and theory. 16,17 The 4d and 5d TMs (Ru, Rh, and Pd [10][11][12][13] and Os, Ir, and Pt 14,15 ) isovalent to Fe, Co, and Ni exhibit ferromagnetic (FM) ground states at certain thicknesses.…”

Section: Introductionmentioning

confidence: 99%

Extremely large perpendicular magnetic anisotropy of an Fe(001) surface capped by5dtransition metal monolayers: A density functional study

et al. 2013

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Significant enhancement of the magnetocrystalline anisotropy (MCA) of an Fe(001) surface capped by 4d and 5d transition metal monolayers is presented in this study using first principles density functional calculations. In particular, an extremely large perpendicular MCA of +10 meV/Ir was found in Ir-capped Fe(001), which originates not from the Fe but from the large spin-orbit coupling of the Ir atoms. From the spin-channel decomposition of the MCA matrix and electronic structure analyses, we find that strong 3d-5d band hybridization in the minority spin state is responsible for the sign changes of the MCA from parallel to perpendicular.

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Spin torque switching of perpendicular Ta∣CoFeB∣MgO-based magnetic tunnel junctions

Cited by 660 publications

References 14 publications

Switching field distributions with spin transfer torques in perpendicularly magnetized spin-valve nanopillars

Switching field distributions with spin transfer torques in perpendicularly magnetized spin-valve nanopillars

Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance

Extremely large perpendicular magnetic anisotropy of an Fe(001) surface capped by5dtransition metal monolayers: A density functional study

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