Switching Of Magnetic Vortex Core Research Articles

Nanocavity-Mediated Fast Magnetic Vortex Core In-Situ Switching by Local Magnetic FieldSupported by the Fund of Key Laboratory of Advanced Materials of Ministry of Education (Grant No. ADV21-20).

Fast in situ switching of magnetic vortex core in a ferromagnetic nanodisk assisted by a nanocavity, with diameter comparable to the dimension of a vortex core, is systematically investigated by changing the strength as well as the diameter of the effective circular region of the applied magnetic field. By applying a local magnetic field within a small area at the nanodisk center, fast switching time of about 35 ps is achieved with relatively low field strength (70 mT) which is beneficial for fast data reading and writing. The reason for this phenomenon is that the magnetic spins around the nanocavity is aligned along the cavity wall due to the shape anisotropy when the perpendicular field is applied, which deepens the dip around the vortex core, and thus facilitates the vortex core switching.

Unidirectional switching of magnetic vortex core in a nanocavity mediated nanodisk: Looking for a reliable low-power-driven and fast switching in terms of geometric parameters

Reliable unidirectional switching of magnetic vortex core driven by continuous rotating magnetic field is investigated using a permalloy nanodisk with a nanocavity inserted in the center in combination with micromagnetic simulations. It is reported that once the vortex core is confined in a nanocavity of diameter is comparable to the core size, the modes of the core motion (divergence/convergence modes) are modulated differently by the nanocavity: the threshold field amplitude required for vortex core switching is reduced for convergence mode, but not for divergence mode. We found that the confinement of the nanocavity to the core is mediated by the cavity height as well. Low-power-driven fast unidirectional switching is found to be achievable by carefully choosing the value of the nanocavity height.

Periodic vortex core switching in curved magnetic nanodisk

Periodic switching of magnetic vortex core driven by alternative magnetic field, applied perpendicularly, is investigated in a curved permalloy nanodisk by using micromagnetic simulation. Modulated by the curvature, the oscillations of the out-of-plane magnetization, caused by the external magnetic field, are confined in the center region, closed to the core, which reduces the threshold switching field down to 3 mT. While, the excitation of radial spin waves after a core switching dominates the reversal process generally in flat nanodisks, making it hard to control the final core polarity. The released spin waves in the center region during the core switching are relatively weak in curved nanodisk with most of radial spin waves dissipated to the thick edge part, resulting in a stable periodic vortex core switching.

Unidirectional switching of magnetic vortex core confined in a cylindrical nanocavity

Ultrafast unidirectional reversal of magnetic vortex core confined in a cylindrical nanocavity is numerically investigated using micromagnetic simulations for the permalloy nanodisk. The excited modes (convergence/divergence) of the core motion are modulated differently by the cavity, depending on the dimension of the cavity, which is the main reason for the unidirectional vortex polarization switching. Assisted with the cavity, the core can be reversed well below 200 ps with less than 10 mT external magnetic field and over a wide range of field frequency. In particular, the core can be selectively switched by varying the dimension of the cylindrical cavity.

Optical Quenching of Magnetic Vortex Visualized In Situ by Lorentz Electron Microscopy

Understanding the fundamental dynamics of topological vortex and antivortex naturally formed in micro/nanoscale ferromagnetic building blocks under external perturbations is crucial to magnetic vortex based information processing and spintronic devices. All previous studies have focused on magnetic vortex-core switching via external magnetic fields, spin-polarized currents, or spin waves, which have largely prohibited the investigation of novel spin configurations that could emerge from the ground states in ferromagnetic disks and their underlying dynamics. Here, we report in situ visualization of femtosecond laser quenching induced magnetic vortex change in various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using 4D electron microscopy. Besides the switching of magnetic vortex chirality and polarity, we observed with distinct occurrence frequencies a plenitude of complex magnetic structures that have never been observed by magnetic field or current assisted switching. These complex magnetic structures consist of a number of newly created topological magnetic defects (vortex and antivortex) strictly conserving the topological winding number, demonstrating the direct impact of topological invariant on the magnetization dynamics in ferromagnetic disks. Their spin configurations show mirror or rotation symmetry due to the geometrical confinement of the disks. Combined micromagnetic simulations with the experimental observations reveal the underlying magnetization dynamics and formation mechanism of the optical quenching induced complex magnetic structures. Their distinct occurrence rates are pertinent to their formation-growth energetics and pinning effects at the disk edge. Based on these findings, we propose a paradigm of optical-quenching-assisted fast switching of vortex cores for the control of magnetic vortex based information recording and spintronic devices.

Faster vortex core switching with lower current density using three-nanocontact spin-polarized currents in a confined structure**Project supported by the China Postdoctoral Science Foundation (Grant No. 2013M541286), the Science and Technology Planning Project of Jilin Province, China (Grant Nos. 20140520109JH and 20150414003GH), and the “Twelfth Five year” Scientific and Technological Research Project of Department of Education of Jilin Province, China.

We perform micromagnetic simulations on the switching of magnetic vortex core by using spin-polarized currents through a three-nanocontact geometry. Our simulation results show that the current combination with an appropriate current flow direction destroys the symmetry of the total effective energy of the system so that the vortex core can be easier to excite, resulting in less critical current density and a faster switching process. Besides its fundamental significance, our findings provide an additional route to incorporating magnetic vortex phenomena into data storage devices.

Switching of magnetic vortex core in elliptical disks by nanosecond field pulses

We report the switching of a magnetic vortex core in ferromagnetic elliptical disks induced by a nanosecond field pulse. We show that the switching probability depends on both the duration and amplitude of the field pulse. The minimum magnetic field required for the core switching depends also on the ellipticity of the disk. Micromagnetic simulations reproduce this behavior and reveal that there are two mechanisms of the core switching.

Switching of magnetic vortex core in a Pac-man disk using a single field pulse

We report on the switching of the magnetic vortex core in a Pac-man disk using a magnetic field pulse, investigated via micromagnetic simulations. The minimum core switching field is reduced by 72% compared with that of a circular disk with the same diameter and thickness. However, the core switches irregularly with respect to both the field pulse amplitude and duration. This irregularity is induced by magnetization oscillations that arise owing to the excitation of spin waves when the core annihilates. We show that the core switching can be controlled with the assist magnetic field and by changing the waveform.

Current-induced switching of magnetic vortex core in ferromagnetic elliptical disks

We report the experimental observation and micromagnetics simulation of the current-induced switching of the magnetic vortex core in ferromagnetic elliptical disks. We found that the critical current density required for the core switching depends on the relative alignment between the current direction and the elliptical axes of the disk. The micromagnetics simulation results qualitatively reproduce the experimental findings, suggesting that the vortex core displacement induced by the current plays a significant role for the core switching rather than the core velocity.