NEWS EDITOR’S CHOICE SCIENTISTS CREATE MAGNETIC SYSTEM TRANSFORMING HEAT INTO MOTION


rotated in only one of two possible directions, without an obvious reason why one way should be preferred over the other. Sebastian Gliga, the lead author of the study


and Marie Curie Research Fellow at the University of Glasgow, recalls: “The system we have studied is an artificial spin ice, a class of geometrically frustrated magnetic materials. “We were surprised to see that the geometry of


A


team of scientists have found a new way to transform ambient heat into motion in


nanoscale devices – a discovery which could open up new possibilities for data storage, sensors, nanomotors and other applications in the ever- shrinking world of electronics. In a new paper published in the journal Nature


Materials, an international team of researchers from various institutes including the University of Glasgow and the University of Exeter in the UK, and from the ETH Zurich and the Paul Scherrer Institute in Switzerland, describe how they have created a magnetic system capable of extracting thermal energy on the nanoscale, using the concept of a gear known as a ratchet, and turning magnetic energy into the directed rotation of the magnetisation. The thermal ratchet was realised in a material


known as ‘artificial spin ice’, made of an assembly of tiny nanomagnets of Permalloy, a nickel–iron alloy. The individual nanomagnets are just 470 nanometres long (or about 200 times smaller than the diameter of a human hair) and 170 nanometres wide, with only a single magnetic domain; that is, the magnetisation can only point in one of two directions along the long axis of the magnet. After magnetising their sample, the researchers observed that the magnetisation


the interactions can be tailored to achieve an active material that exhibits dynamic chirality and thus acts as a ratchet.” Chirality means that an object looks different to its mirror image, like our left and right hands. Chirality can also occur in motion: the best-known example is the rattleback, a boat-shaped top that prefers to spin in a single direction. Professor Robert Stamps of the University of


Manitoba (previously of University of Glasgow) pointed out that it is the properties of the edges of the assembly that determine the thermal ratchet behaviour. “We suspected from the beginning that the boundaries would strongly affect the magnetic ordering and the dynamics.” It was this idea and proposal of the geometry


from Prof. Stamps that eventually led to the intriguing behaviour measured by researchers. The mechanism leading to the observed


behaviour was not obvious, however, and it is only through numerical modelling that the precise role of the edges became clear. According to Professor Gino Hrkac, second author on the report, from University of Exeter and Royal Society Research Fellow, “We tried to understand for quite some time how the system worked before we realised that the edges created an asymmetric energy potential.” This asymmetry is reflected in the distribution of the magnetic field at the boundaries of the


nanomagnet array and causes the magnetisation to rotate in a preferred direction. To image the evolution of the magnetic state of


the system, the scientists used x-rays and the so- called magnetic dichroic effect. The measurements were carried out at the synchrotron light source SLS at the Paul Scherrer Institute in Switzerland and at the Advanced Light Source, Lawrence Berkeley National Laboratory in the United States. According to Professor Laura Heyderman of the


ETH Zurich and Paul Scherrer Institute: “Artificial spin ice has mainly been used to answer scientific questions, for example concerning the physics of frustration. This is a nice demonstration of how artificial spin ice can be a functional material and provides a step towards applications.” These findings establish an unexpected route to


transforming magnetic energy into the directed motion of magnetisation. The effect now found in the two-dimensional magnetic structures comes with the promise that it will be of practical use in nanoscale devices, such as magnetic nanomotors, actuators, or sensors. Indeed, because angular momentum is conserved and spin is a type of angular momentum, the change in the magnetic moment of the system can in principle induce a physical rotation of the system (through the Einstein–de Haas effect). It may also find applications in magnetic memory where bits could be stored through local heating with laser pulses. The paper, titled ‘Emergent dynamic chirality in


a thermally driven artificial spin ratchet’, is published in Nature Materials. The work was funded by the European Union’s Horizon 2020 research and innovation programme, the Engineering and Physical Sciences Research Council (EPSRC), the Vienna Science and Technology Fund and the Royal Society. www.gla.ac.uk


FLUORESCENT TAGS AND NANOPARTICLES COMPARED AS BIOLOGICAL TOOLS


A Prior stage has been used in a ground-breaking study comparing traditional fluorescent tags to Surface Enhanced Raman Scattering Nanoparticles (SERS NPs), which found there were significant differences between the two imaging methods. Prior Scientific’s’S H117 motorised precision stage was used in a study comparing the characteristics of traditional fluorescent probes with SERS NPs, in which the two methods were used to fluorescently image both live and fixed cells. Interest in using SERS NPs rather than


traditional fluorescent tags in biological imaging 14 WINTER 2017 | MICROMATTERS


is growing, due to the nanoparticles’ stability and the narrow spectral features that they display. Maria Navas-Moreno and colleagues at the University of California Davis Centre for Biophotonics compared fluorescent probes and SERS NPs, showing that the two methods produced similar results in fixed cells, but dramatically different patterns when used on live cells. This research, published in Scientific Reports, demonstrates that unexpected cellular interactions with nanoparticles must be taken into account, before using SERS as an alternative to traditional probes. A home build Raman microscopy system,


incorporating an H117 stage, was a key part of this system. Especially important from Maria’s view was that the H117’s large travel range (114 x 75mm) ensured that a large field of view was easy to image. Manuj Patel, Global Strategic Marketing Manager for Prior Scientific, says:


“The H117 stage is frequently the stage of choice for live cell imaging, as it offers a combination of speed, easy integration into numerous imaging packages via the ProScan III control system, and precision positioning, with a repeatability of just 0.2um, and a metric accuracy of 0.059 um/mm. I’m very grateful to Maria and her colleagues for sharing their interesting research with us, as well as providing such positive feedback on our products.” Prior Scientific Instruments has been


manufacturing precision scientific and optical instruments since 1919. With a large manufacturing facility in Cambridge and business units in the USA, Germany and Japan, Prior Scientific produces precisions stages, focussing devices, illumination solutions, robotic loaders and other solutions, allowing automation of extensive microscopes from world leading manufacturers. www.prior.com


/MICROMATTERS


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