arXiv subjects

Mengxing Wang

Publications and source records attributed to Mengxing Wang.

5 recordsLinked to original sources

arXiv2019

Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture

Spin-torque memristors were proposed in 2009, which could provide fast, low-power and infinite memristive behavior for large-density non-volatile memory and neuromorphic computing. However, the strict requirements of combining high magnetoresistance, stable intermediate states and spin-polarized current switching in a single device pose difficulties in physical implementation. Here, we experimentally demonstrate a nanoscale spin-torque memristor based on a perpendicular-anisotropy magnetic tunnel junction with a CoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance is higher than 200%, and memristive behavior can be realized by spin-transfer torque switching. Memristive states are maintained by robust domain wall pinning around clusters of W atoms, where nanoscale vertical chiral spin textures could be formed through the competition between opposing Dzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling caused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB free layers. Spike-timing-dependent plasticity is also demonstrated in this device.

physics.app-ph↗

arXiv2019

Magnetization dynamics modulated by Dzyaloshinskii-Moriya interaction in the double-interface spin transfer torque magnetic tunnel junction

Currently double-interface MTJs have been developed for enhancing the thermal stability barrier in small technology node. Dzyaloshinskii-Moriya interaction (DMI) inevitably exists in such devices due to the use of the heavy-metal/ferromagnet structures. Previous studies have demonstrated the detrimental effect of DMI on the conventional single-interface spin transfer torque (STT) MTJs. Here in this work we will prove that the detrimental effect of the DMI could be almost eliminated in the double-interface STT-MTJ. This conclusion is attributed to the suppressing effect of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction on the DMI. Detailed mechanisms are analyzed based on the theoretical models and micromagnetic simulation results. Our work highlights the importance of appropriately controlling the DMI in two free layers of the double-interface STT-MTJ.

physics.app-ph↗

arXiv2018

Field-free switching of perpendicular magnetic tunnel junction by the interplay of spin orbit and spin transfer torques

Spin-orbit torque and spin-transfer torque are leading the pathway to the future of spintronic memories. However, both of the mechanisms are suffering from intrinsic limitations. In particular, an external magnetic field is required for spin-orbit torque to execute deterministic switching in perpendicular magnetic tunnel junctions; the demand for reduced spin-transfer torque switching current to realize ultralow power is still remaining. Thus, a more advanced switching mechanism is urgently needed to move forward spintronics for wide applications. Here, we experimentally demonstrate the field-free switching of three-terminal perpendicular-anisotropy nanopillar devices through the interaction between spin-orbit and spin-transfer torques. The threshold current density of spin-transfer torque switching is reduced to 0.94 MA.cm-2, which is a significant decrease compared to that in other current-induced magnetization switching mechanisms. In addition, thanks to the interplay of spin-orbit and spin-transfer torques, lower current-induced switching in the conventional two-terminal perpendicular magnetic tunnel junctions is also achieved.

physics.app-ph↗

arXiv2018

Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance

Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of particular interest for magnetic random-access memories because of their excellent thermal stability, scaling potential, and power dissipation. However, the major challenge of current-induced switching in the nanopillars with both a large tunnel magnetoresistance ratio and a low junction resistance is still to be met. Here, we report spin transfer torque switching in nano-scale perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to 249% and a resistance area product as low as 7.0 Ω.μm2, which consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient resonant tunnelling transmission induced by the atom-thick W layers could contribute to the larger magnetoresistance ratio than conventional structures with Ta layers, in addition to the robustness of W layers against high temperature diffusion during annealing. The switching critical current density could be lower than 3.0 MA.cm-2 for devices with a 45 nm radius.

physics.app-ph↗

arXiv2017

Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbital coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

cond-mat.mtrl-sci↗