A novel method for the injection and manipulation of magnetic charge states in nanostructures

Abstract

Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360° domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method’s efficacy via the injection and spatial manipulation of 360° domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.

Half-hedgehog spin textures in sub-100 nm soft magnetic nanodots

“…This phenomenon has been observed in previous works, where the local field of the MFM tip was used to manipulate the magnetic charges. 47,48 In this work, the tip stray field serves as a tool to create and enhance the stability of the configurations. The set of images from Fig.…”

Current-controlled nanomagnetic writing for reconfigurable magnonic crystals

“…Upon reaching the island end the ±1/2 defects are free to reach and annihilate each other, unwinding the i-DW to a collinear state and emitting a spin-wave burst down the nanoisland (t = 0.9 ns). The spin-wave burst interacts with the remaining i-DW 39,41,45 , exerting a torque that accelerates it towards the nanoisland bottom (t = 1.3 ns). As the remaining i-DW approaches the nanoisland bottom, it is increasingly magnetostatically attracted to it, further driving acceleration (t = 2.0 ns) until the i-DW unwinds on contact as described above, leaving a DW-free nanoisland magnetized antiparallel to its initial state (t = 2.5 ns) with reversal completed 2 ns after the c-DW reaches the nanoisland.…”

“…We have focused here on magnetic reversal of Ising-like nanoelements. Prior studies have demonstrated injection of 360°DWs 41 and Skyrmions using related locally divergent stray fields (magnetic force microscope tips in these cases) in nanostructures and writing states in nanodisks 70 . The DW-based writing method is highly suitable for integration with such writing schemes, offering substantial future scope.…”

“…Many approaches struggle to function without disturbing delicate magnetic states elsewhere in the system due to large stray fields or a reliance on global external fields. The remaining methods rely on mechanical apparatus orders of magnitude larger than the nanomagnet, either a hard-disk style write-head or scanning-probe with magnetic tip [39][40][41] -unsuitable for on-chip integration and susceptible to damage.…”

Tunable magnetization dynamics in artificial spin ice via shape anisotropy modification

“…However, reliably accessing more than a handful of microstates beyond simple global field saturation has proved difficult, with either stochastic AC demagnetization protocols or complex rotating field sequences employed [21,22]. Total microstate control via individual nanowire reversal using magnetic force microscope tips has been demonstrated [23][24][25] but is time consuming and is unsuitable for device integration. Considering ASI as an RMC rather than a model system for geometric frustration, it becomes attractive to modify the aspect ratio and hence the shape anisotropy of each nanowire sublattice, forgoing * troy.dion.16@ucl.ac.uk degenerate dipolar interactions for the microstate control afforded by the different coercive fields between each modified sublattice.…”