Artificial Frustrated Systems

Focus on artificial frustrated systems.
J Cumings, L J Heyderman, C H Marrows and R L Stamps
New J. Phys. 16, 075016 (2014)

Artificial spin ices. (a) XMCD-PEEM image of artificial spin ice, captured in the so-called 'string regime' [7], while undergoing thermal relaxation from an energetically excited, saturated moment, configuration down to one of the two degenerate ground states. Nanomagnets with moments pointing towards the bottom/left appear in blue contrast, while nanomagnets with moments pointing up/right appear in red contrast. Scale bar 2 μm. (b) X-ray transmission micrograph of a CoFeB artificial square ice with the overlaid red gridlines showing the square lattice. Magnetic contrast is shown in the inset, where islands that have reversed under thermal excitation at 100 °C appear with bright contrast. Scale bar 1 μm. (c) Lorentz transmission electron micrograph of artificial kagome ice after thermal excitation. The magnetization direction within the arms of the array can be determined from the detailed intensity profile across the arm [8], allowing the magnetic charge at each vertex to be inferred. Positive and negative magnetic charges are indicated by the overlaid red and blue dots, showing that the sample is in the charge-ordered, kagome ice-II state. Scale bar 500 nm. (d) The number of configurations that can be created in an artificial square ice by an applied field is very sensitive to disorder. The diagram represents all possible configurations that can be realized by application of the field (with magnitude slightly larger than the mean coercive field) to sixteen elements starting from a saturated type II state with a distribution of switching fields. Each unique configuration is indicated by a circular dot