23. October 2017
Magnetic structures take a new turnThe unexpected finding that in an ‘artificial spin ice’ magnetostatic energy can be transformed into directed rotation of magnetization provides fresh insights into such nano-patterned magnetic structures — and might enable novel applications in nanoscale devices.
Magnetism and rotation are intimately related. This connection can lead to surprising and non-intuitive effects, as first demonstrated a century ago, when it was predicted, and observed, that changing the magnetization in a piece of ferromagnetic material (such as iron) rotates it, ever so slightly; conversely, spinning a non-magnetised piece of the same material magnetizes it. These phenomena are known as Einstein—de Haas and Barnett effects, respectively, and are beautiful phenomena described in many physics textbooks. Now, Sebastian Gliga and colleagues in the Laboratory for Multiscale Materials Experiments at PSI, led by of Laura Heyderman, report in Nature Materials  the discovery of another sort of rotation in a magnetic structure, one that came as a surprise. They observed that after magnetising their sample, the magnetisation started to consistently rotate in one of two possible directions, without an obvious reason why one way should be preferred over the other.
Nano-tailored magnetic materials
In such artificial spin-ice structures, Gliga and co-workers have now observed that when the total magnetisation (that of all nanomagnets taken together) is initially set by an external field to point in one direction, it then starts to rotate clockwise once that field is removed. The rotation stops at some point, but when the spin ice is heated up, the magnetisation continues to rotate in the same direction, until it has rotated by 180°.
A practical spin on a fundamental finding
Taken together, these findings establish an unexpected route to transform magnetostatic energy (provided by the initial magnetic field) into directed motion of magnetization. And whereas the significance of Einstein–de Haas and Barnett effects remain largely confined to the realm of textbooks, the effect now found in the two-dimensional magnetic structures comes with the promise to be of practical use in nanoscale devices, including magnetic nanomotors, actuators, sensors and data storage.
This work was carried out in a collaboration led by Sebastian Gliga (Marie Curie Research Fellow at the University of Glasgow, UK, and visiting scientist at PSI) and Laura Heyderman (PSI and ETH Zurich), involving Robert Stamps of the University of Glasgow, now at the University of Manitoba, Canada (theory) and Gino Hrkac of the University of Exeter, UK (numerical modelling). Soft x-ray photoemission electron microscopy was carried out at the SIM beamline of the Swiss Light Source at PSI and at the Advanced Light Source, Berkeley National Laboratory, US.
ContactDr. Sebastian Gliga
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 2056, e-mail: firstname.lastname@example.org
Original Publication1. Emergent dynamic chirality in a thermally driven artificial spin ratchet
Gliga S, Hrkac G, Donnelly C, Büchi J, Kleibert A, Cui J, Farhan A, Kirk E, Chopdekar RV, Masaki Y, Bingham NS, Scholl A, Stamps RL and Heyderman LJ
Nature Materials, DOI: 10.1038/nmat5007 (2017).
Additional readingArtificial spin ice: A ratchet made of tiny magnets (News & Views article)
Nature Materials, DOI: 10.1038/nmat5004 (2017).