We analyse the appearance of a mechanical torque that acts on a chiral molecule: a single-stranded DNA, in which the spin-orbit interaction is expected to induce a spin-selectivity effect. The mechanical torque is shown to appear as a result of the non-conservation of the spin current in the presence of the spin-orbit interaction. Adopting a simple microscopic model Hamiltonian for a chiral molecule connected to source and drain leads, and accounting for the mechanical torque acting on the chiral molecule as the back action on the electrons traversing the molecule, we derive the spin continuity-equation. It connects the spin current expressed by a Landauer-type formula and the mechanical torque. Thus, by injecting a spin-polarized current from the source electrode, it is possible to generate a torque, which will rotate the DNA molecule.
Ferromagnetic spin-valves and tunneling junctions are crucial for spintronics applications and are one of the most fundamental spintronics devices. Motivated by the potential unique advantages of antiferromagnets for spintronics, we theoretically study here junctions built out of non-collinear antiferromagnets. We demonstrate a large and robust magnetoresistance and spin-transfer torque capable of ultrafast switching between parallel and anti-parallel states of the junction. In addition, we show that the non-collinear order results in a spin-transfer torque that is in several key aspects diffe…
We study the current-induced torques in asymmetric magnetic tunnel junctions containing a conventional ferromagnet and a magnetic Weyl semimetal contact. The Weyl semimetal hosts chiral bulk states and topologically protected Fermi arc surface states which were found to govern the voltage behavior and efficiency of current-induced torques. We report how bulk chirality dictates the sign of the non-equilibrium torques acting on the ferromagnet and discuss the existence of large field-like torques acting on the magnetic Weyl semimetal which exceeds the theoretical maximum of conventional magnetic…
Current-induced switching of magnetic tunnel junctions: Effects of field-like spin-transfer torque, pinned-layer magnetization orientation and temperature
First-principles spin-transfer torque in CuMnAs$|$GaP$|$CuMnAs junctions
我们证明了电流垂直于平面几何的全反铁磁隧道结可以用作具有潜在高频操作的高效自旋电子学器件。通过使用最先进的密度泛函理论结合量子输运，我们证明了电极的Néel矢量可以通过自旋转移矩来操纵。这在两个不同的磁性子晶格上交错，并且可以产生动力学和切换。同时利用标准隧道磁阻效应可以读出结的不同磁化状态。计算了在反铁磁CuMnAs电极和GaP隔离层之间具有不同表面终端的CuMnAs $|$ GaP $|$ CuMnAs结。特别是，我们发现，扭矩仍然交错的终止，而磁阻取决于界面的微观细节。
Impact of current paths on measurement of tunneling magnetoresistance and spin torque critical current densities in GaMnAs-based magnetic tunnel junctions
A three-dimensional self-consistent spin transport model is developed, which includes both tunnelling transport, as well as metallic transport. Using the spin accumulation computed either side of a tunnel barrier, spin torques are obtained, and it is shown the model reproduces both damping-like and field-like spin-transfer torques, with the expected sinusoidal angular dependence, and inverse ferromagnetic layer thickness dependence. An explicit solution to the drift-diffusion model is derived, which allows analysing the effect of both the reference and free layer thickness on the spin-transfer…
Temperature plays an important role in spin torque switching of magnetic tunnel junctions causing magnetization fluctuations that decrease the switching voltage but also introduce switching errors. Here we present a systematic study of the temperature dependence of the spin torque switching probability of state-of-the-art perpendicular magnetic tunnel junction nanopillars (40 to 60 nm in diameter) from room temperature down to 4 K, sampling up to a million switching events. The junction temperature at the switching voltage---obtained from the thermally assisted spin torque switching model---sa…
Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions
采用第一性原理非共线波函数匹配方法，研究了CoFe/Mg-B-O/CoFe（001）磁性隧道结（MTJ）中的自旋转移矩（STT），其中考虑了三种不同类型的B掺杂MgO，包括B原子取代Mg原子Mg（$_3$ BO $_4$）、B原子替代MgO中的O原子（Mg $_4$ BO $_3$）和B原子占据MgO中的间隙位置（Mg $_4$ BO $_4$）。在弹道CoFe/Mg $_3$ BO $_4$和基于CoFe/Mg $_4$ BO $_4$的MTJ中都可以获得很强的非对称角度依赖性的STT，而在基于CoFe/Mg $_4$ BO $_3$的结中观察到几乎对称的STT曲线。此外，B分布的无序性可以显著抑制STT角度依赖性的不对称性。CoFe/Mg-B-O/CoFe MTJ中STT的这种偏斜可以归因于B扩散到MgO间隔层中引起的界面共振态。研究表明，在MgO基自旋力矩振荡器（STO）中引入B原子可以有效地提高微波输出功率。
Since the discovery of the spin orbit torque (SOT) induced by spin Hall effect in heavy metals, much effort has been devoted to understanding the mechanism of the charge-to-spin conversion as well as to developing new schemes for high speed, low energy magnetic recording technologies. While fast switching has been demonstrated in three terminal magnetic tunnel junctions (3T-MTJs) through applying short voltage pulses in the heavy metal channel, detailed understanding of the switching mechanism is lacking due to the complexity of the multi-layered magnetic structure and the three-terminal geome…
There are pressing problems with traditional computing, especially for accomplishing data-intensive and real-time tasks, that motivate the development of in-memory computing devices to both store information and perform computation. Magnetic tunnel junction (MTJ) memory elements can be used for computation by manipulating a domain wall (DW), a transition region between magnetic domains. But, these devices have suffered from challenges: spin transfer torque (STT) switching of a DW requires high current, and the multiple etch steps needed to create an MTJ pillar on top of a DW track has led to r…
This work investigates nanosecond superparamagnetic switching in 50 nm diameter in-plane magnetized magnetic tunnel junctions (MTJs). Due to the small in-plane uniaxial anisotropy, dwell times below 10 ns and auto-correlation times down to 5 ns are measured for circular superparamagnetic tunnel junctions (SMTJs). SMTJs exhibit probabilistic switching of the magnetic free layer, which can be used for the generation of true random numbers. The quality of random bitstreams, generated by our SMTJ, is evaluated with a statistical test suite (NIST STS, sp 800-22) and shows true randomness after thre…
A technique is presented, which creates MCB junctions that can be pivoted to any desirable angle. The MCB junction equipped with a specific glass liquid cell can be used to produce a MCB junction, of which the electrodes are covered with a microscopic layer of fluid, thus producing a partially wet phase MCB junction.
Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in nonvolatile magnetic random access memories. In order to develop faster memory devices, an improvement of the timescales underlying the current driven magnetization dynamics is required. Here we report all-electrical time-resolved measurements of magnetization reversal driven by SOT in a three-terminal MTJ device. Single-shot measurements of the MTJ resistance during current injection reveal that SOT switching involves a stochastic two-step process con…
