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Cascales J.P.,Autonomous University of Madrid | Herranz D.,Autonomous University of Madrid | Sambricio J.L.,Autonomous University of Madrid | Ebels U.,CNRS Spintronics and Technology of Components | And 2 more authors.
Applied Physics Letters

We report on room temperature magnetoresistance and low frequency noise in sub-100 nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin (0.9 nm) barriers. For magnetic fields applied along the hard axis, we observe current induced magnetization switching between the antiparallel and parallel alignments at dc current densities as low as 4 × 106 A/cm 2. We attribute the low value of the critical current to the influence of localized reductions in the tunnel barrier, which affects the current distribution. The analysis of random telegraph noise, which appears in the field interval near a magnetization switch, provides an estimate to the dimension of the pseudo pinholes that trigger the magnetization switching via local spin torque. Micromagnetic simulations qualitatively and quantitatively reproduce the main experimental observations. © 2013 American Institute of Physics. Source

Thiaville A.,University Paris - Sud | Rohart S.,University Paris - Sud | Jue E.,CNRS Spintronics and Technology of Components | Cros V.,University Paris - Sud | Fert A.,University Paris - Sud

We explore a new type of domain wall structure in ultrathin films with perpendicular anisotropy, that is influenced by the Dzyaloshinskii-Moriya interaction due to the adjacent layers. This study is performed by numerical and analytical micromagnetics. We show that these walls can behave like Néel walls with very high stability, moving in stationary conditions at large velocities under large fields. We discuss the relevance of such walls, that we propose to call Dzyaloshinskii domain walls, for current-driven domain wall motion under the spin Hall effect. © Copyright EPLA, 2012. Source

Kalitsov A.,University of Puerto Rico at San Juan | Silvestre W.,University of Puerto Rico at San Juan | Chshiev M.,CNRS Spintronics and Technology of Components | Velev J.P.,University of Puerto Rico at San Juan | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics

We derive expressions for both parallel and perpendicular components of spin transfer torque (STT) in magnetic tunnel junctions (MTJs), which have several important advantages over the currently available expressions: First they are derived in a more realistic approximation, resulting in excellent agreement with exact results even in the presence of resonant tunneling. Second, we show that they can be expressed in terms of the scattering matrix elements, which gives them a clear physical interpretation. Third, they are given entirely in terms of collinear quantities, which are readily available in existing transport codes. We use these expressions to investigate STT behavior in MTJs with asymmetric barriers at finite bias. The results show that lowering the barrier height in the bulk does not qualitatively change the behavior of STT. The absolute STT increases on account of the overall increase of the barrier transparency; however, the STT efficiency remains in the same range. At the same time, modifications of the interfaces can qualitatively change STT behavior. Thus, interface engineering can be used to control the bias dependence of STT and optimize the performance of STT-based devices. © 2013 American Physical Society. Source

Garello K.,Catalan Institute of Nanoscience and Nanotechnology | Miron I.M.,CNRS Spintronics and Technology of Components | Avci C.O.,Catalan Institute of Nanoscience and Nanotechnology | Freimuth F.,Julich Research Center | And 8 more authors.
Nature Nanotechnology

Recent demonstrations of magnetization switching induced by in-plane current injection in heavy metal/ferromagnetic heterostructures have drawn increasing attention to spin torques based on orbital-to-spin momentum transfer. The symmetry, magnitude and origin of spin-orbit torques (SOTs), however, remain a matter of debate. Here we report on the three-dimensional vector measurement of SOTs in AlO x/Co/Pt and MgO/CoFeB/Ta trilayers using harmonic analysis of the anomalous and planar Hall effects. We provide a general scheme to measure the amplitude and direction of SOTs as a function of the magnetization direction. Based on space and time inversion symmetry arguments, we demonstrate that heavy metal/ferromagnetic layers allow for two different SOTs having odd and even behaviour with respect to magnetization reversal. Such torques include strongly anisotropic field-like and spin transfer-like components, which depend on the type of heavy metal layer and annealing treatment. These results call for SOT models that go beyond the spin Hall and Rashba effects investigated thus far. © 2013 Macmillan Publishers Limited. All rights reserved. Source

Miron I.M.,CNRS Spintronics and Technology of Components | Miron I.M.,Catalan Institute of Nanoscience and Nanotechnology | Moore T.,CNRS Spintronics and Technology of Components | Moore T.,CNRS Neel Institute | And 10 more authors.
Nature Materials

The propagation of magnetic domain walls induced by spin-polarized currents has launched new concepts for memory and logic devices. A wave of studies focusing on permalloy (NiFe) nanowires has found evidence for high domain-wall velocities (100 ms-1; refs 10, 11), but has also exposed the drawbacks of this phenomenon for applications. Often the domain-wall displacements are not reproducible, their depinning from a thermally stable position is difficult and the domain-wall structural instability (Walker breakdown) limits the maximum velocity. Here, we show that the combined action of spin-transfer and spin-orbit torques offers a comprehensive solution to these problems. In an ultrathin Co nanowire, integrated in a trilayer with structural inversion asymmetry (SIA), the high spin-torque efficiency facilitates the depinning and leads to high mobility, while the SIA-mediated Rashba field controlling the domain-wall chirality stabilizes the Bloch domain-wall structure. Thus, the high-mobility regime is extended to higher current densities, allowing domain-wall velocities up to 400ms-1. © 2011 Macmillan Publishers Limited. All rights reserved. Source

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