Engineering topics

Wen, Yan

Publications and source records attributed to Wen, Yan.

3 records

DOE OSTI2023

Nonvolatile Magnetoelectric Switching of Magnetic Tunnel Junctions with Dipole Interaction

The magnetoelectric effect is technologically appealing because of its ability to manipulate magnetism using an electric field rather than magnetic field or current, thus providing a promising solution for the development of energy-efficient spintronics. Although 180° magnetization switching is vital to spintronic devices, the achievement of 180° magnetization switching via magnetoelectric coupling is still a fundamental challenge. Here, in this work, voltage-driven full resistance switching of a magnetic tunnel junction (MTJ) with dipole interaction on a ferroelectric substrate through switchable parallel/antiparallel magnetization alignment is demonstrated. Parallel magnetization alignment along the y direction is obtained under a bias magnetic field. By rotating the magnetic easy axis via strain-mediated magnetoelectric coupling, the parallel magnetizations in the MTJ reorient to the x axis with opposite paths because of dipole interaction, thus resulting in antiparallel alignment. Moreover, this voltage switching of MTJs is nonvolatile owing to variations in dipole interaction and can be well understood via phase field simulations. The results provide an avenue to realize electrical switching of MTJs and are significant for exploring energy-efficient spintronic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2022

High‐Efficiency Magnon‐Mediated Magnetization Switching in All‐Oxide Heterostructures with Perpendicular Magnetic Anisotropy

Abstract The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron‐mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all‐oxide heterostructures of SrRuO 3 /NiO/SrIrO 3 are epitaxially grown on SrTiO 3 single‐crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO 3 with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO 3 with strong spin–orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion‐related energy dissipation from electron‐mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all‐oxide spintronic devices operated by magnon current.

Zheng, Dongxing↗

DOE OSTI2020

Deformation of Néel-type skyrmions revealed by Lorentz transmission electron microscopy

Néel-type magnetic skyrmions in multilayers are promising candidates for ultra-low power spintronic devices. To image the Néel-type skyrmions using Lorentz transmission electron microscopy (L-TEM), the samples must be tilted. Thus, the external magnetic field consists of both in-plane and out-of-plane components. To date, it is still not well known on the effect of the in-plane magnetic field on the L-TEM images, leading to ambiguities in retrieving the structure of Néel-type skyrmions. Here, Néel-type skyrmions in three [Pt/Co/Ta]$_{20}$ multilayer samples, with the easy magnetization axis being tuned from the out-of-plane to the in-plane direction by increasing the Co thickness from 1.8 to 2.2 nm, are imaged. When using a smaller defocus value (-2 mm) and a higher magnification (×9100) of L-TEM, a surprising dark-bright-dark-bright double contrasted pattern, instead of the previously reported dark-bright contrasted pattern, is observed. The additional dark-bright contrasted pattern becomes more evident for thicker Co layer samples in which the magnetization axis tilts more toward the in-plane direction. Further analysis, via a combination of magnetic force microscopy experiments, micromagnetic simulations, and micromagnetic analysis to Lorentz TEM simulation, shows that the additional dark-bright features originate from the deformation of the Néel-type skyrmions within an in-plane magnetic field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗