Emergent collective phenomena in artificial spin ice
Peter Schiffer, University of Illinois at Urbana-Champaign (Principal Investigator)
Nitin Samarth, Pennsylvania State University (Co-Investigator)
     This research targets the study of lithographically fabricated arrays known as ‘artificial spin ice’, composed of sheets of of nanometer-scale magnets. Such systems are frustrated by their geometry, in that no set of orientations of the magnetic poles can align the north and south poles of the magnets to be in close proximity for every pair of neighboring magnets. These systems are analogs to a class of magnetic materials in which the lattice geometry similarly frustrates interactions between individual atoms’ magnetism, and in which a wide range of novel physical phenomena have been observed. The advantage to studying lithographically fabricated samples is that they are both designable and resolvable: i.e., we can control the array geometry, and we can also observe how individual elements of the arrays behave.
     The proposed experimental effort will employ a range of techniques including both advanced forms of microscopy that allow us to image the magnetic pole orientation as well as measurements of the electrical resistivity and how that couples to the magnetism. Combined with theoretical modeling of the collective behavior, these measurements will lead to a detailed understanding of the underlying phenomena.
     In the proposed research program, we plan several research thrusts. We will explore the process and nature of thermalization, i.e., using temperature to allow the magnetic moments to fluctuate and change orientation freely. We will use thermalization to both investigate novel arrangements of the magnets that have not previously been explored experimentally and to study the effects of defects and disorder and finite array size in these systems. We will also expand upon our initial studies of magnets whose poles point perpendicular to the plane of the array, taking advantage of new microscopy techniques that we have developed. Finally we will explore the impact of such frustration on how electricity conducts through such arrays of magnets when the magnets are connected together.
     In addition to shedding light on fundamental physics issues regarding frustration, the study of these arrays broadens understanding of complex connected magnetic systems. The flexibility in both the design and measurement of these arrays make them excellent model systems for studying more general complex phenomena that can emerge from simple interactions. We expect that the results of the proposed research will have a far-ranging impact on understanding of magnetism at the nanometer scale, a topic that is highly relevant to technologies such as magnetic recording.