Category Archives: Switching

New paper on

It has been known for over two decades that it is possible to manipulate magnetic order using femtosecond laser pulses. Many groups have demonstrated that single laser pulses can demagnetise a magnet on the picosecond time-scale, with a subsequent recovery of the order proceeding as the sample cools. Such measurements are routinely made these days using a pump-probe setup and detecting a change in the magnetic order through the Kerr effect. However, the pump beam is often micrometres across, hence what is measured is a spatial average. Just how the magnetic structure changes on the nanometre length-scale has, until now, not been well understood.

In a recent article in Nature Communications, in collaboration with several groups across the world, we have recently demonstrated how these magnetic structures vary across the nano-metre to micrometre length-scale and from the femto-second to nano-second time-scale. We have found “evidence of a universal rapid magnetic order recovery in ferrimagnets with perpendicular magnetic anisotropy via nonlinear magnon processes. We identify magnon localisation and coalescence processes, whereby localised magnetic textures nucleate and subsequently interact and grow in accordance with a power law formalism”.

This has been very well explained in this article on the University of Colorado Boulder’s website. The article is open access and hence free for anyone to download and read.

Strain Induced Vortex Core Switching in Planar Magnetostrictive Nanostructures

As part of a collaboration with Diamond Light Source, The University of Nottingham and the University of York this open access article at Physical Review Letters demonstrates the possibility of low energy reversal of magnetic vortex core. The work, lead by Dr Stuart Cavill (The University of York) shows that by applying a time-varying strain to a ferroelectric layer that induces a strain in a magnetostrictive magnetic layer (Galfenol), vortex core dynamics are stimulated. The flux closure state is topologically symmetric and cannot be moved by simply applying a time-varying strain, therefore the symmetry must be broken. We achieved this by applying a gradient to the strain which moves one domain more than another in the vortex alternately. If the strain gradient is large enough the precession of the vortex core can be driven to force the vortex to reverse. Below is a short movie demonstrating the process.

The work was published on the 7th of August 2015 in Physical Review Letters as under the open access under a creative commons license. This was made available through the York open access fund. The work would have not been possible without the funding of the European Framework 7 project (FemtoSpin), the EPSRC, Diamond Light Source and industrial funding from Seagate Technology.

Laser Induced Magnetization Reversal for Detection in Optical Interconnects

The use of optical interconnects has become a front runner to replace more traditional (usually Cu based) electrical interconnects in many modern devices. One of the major drawbacks of optical interconnects is overcoming the need for photodetectors and (power hungry) amplifiers at the receiver. Such detection is in most cases performed by CMOS circuits or direct band gap semiconductors. As part of a collaboration lead by engineers at Purdue University, IN, USA a new use of ultrafast heat induced switching, originally published in Nature Communications, has been proposed as a means of using optical signals directly with standard CMOS circuits.

Schematic view of focusing of the laser beam on the detecting MTJ.
Schematic view of focusing of the laser beam on the detecting MTJ.

 

The data is transmitted using femtosecond laser pulses that induce magnetisation reversal in a magnetic tunnel junction (MTJ) in the receiver. The proposed scheme offers almost a 40% energy improvement over current technology and speeds of up to 5 GBits/sec for a single link. The preprint of the article can be found on arXiv (or downloaded from this link).