Department of Applied Physics

Artifcial Spin Ice

Utilizing frustration by design in 2D and 3D lattices of single-domain Ising-type nanomagnets we explore the real-time dynamics of magnetic excitations in artificial spin ice systems.

Geometrically frustrated systems are characterized by highly degenerate low-energy states and have long fascinated the research community, not only because their behavior is hard to predict, but also because their physics can lead to new exotic states of matter. We study thermodynamically active artificial spin ice systems wherein the degree of frustration is tailored by lattice design. The spin ices are fabricated by electron-beam lithography and their magnetic structure is directly visualized by synchrotron-based photoemission electron microscopy (PEEM). Besides the design of frustration in new lattice geometries such as the dipolar trident and square-kite lattices, we also provided visual evidence of the formation of screened magnetic charge excitations (polarons) in a dipolar dice lattice. Most recently, we demonstrated real-time imaging of emergent magnetic monopole motion in a macroscopically degenerate 3D square lattice. In this work, we showed that magnetic monopoles are free to evolve within a divergence-free vacuum, a magnetic Coulomb phase, for which features in the form of pinch-point singularities in magnetic structure factors are observed.

Representative Publications

1. A. Farhan, A. Scholl, C.F. Petersen, L. Anghinolfi, C. Wuth, S. Dhuey, R.V. Chopdekar, P. Mellado, M.J. Alava, S. van Dijken. Thermodynamics of emergent magnetic charge screening in artificial spin ice, Nature Communications 7, 12635 (2016).

2. A. Farhan, C.F. Petersen, S. Dhuey, L. Anghinolfi, Q.H. Qin, M. Saccone, S. Velten, C. Wuth, S. Gliga, P. Mellado, M.J. Alava, A. Scholl, S. van Dijken.Nanoscale control of competing interactions and geometrical frustration in a dipolar trident lattice, Nature Communications 8, 995 (2017).

3. C.F. Petersen, A. Farhan, S. Dhuey, Z. Chen, M.J. Alava, A. Scholl, and S. van Dijken. Tuningmagnetic ordering in a dipolar square-kite tessellation. Applied Physics Letters 112, 092403 (2018).

4. A. Farhan, M. Saccone, C.F. Petersen, S. Dhuey, R.V. Chopdekar, Y.-L. Huang, N. Kent, Z. Chen, M.J. Alava, T. Lippert, A. Scholl, S. van Dijken. Emergent magnetic monopole dynamics in macroscopically degenerate artificial spin ice. Science Advances 5, eaav6380 (2019).

5. M. Saccone, K. Hofhuis, Y.L. Huang, S. Dhuey, Z.H. Chen, A. Scholl, R.V. Chopdekar, S. van Dijken, A. Farhan. Dipolar Cairo lattice: Geometrical frustration and short-range correlations. Physical Review Materials 3, 104402 (2019).

6. M. Saccone, K. Hofhuis, D. Bracher, A. Kleibert, S. van Dijken, A. Farhan. Elevated effective dimension in tree-like nanomagnetic Cayley structures. Nanoscale (2020).

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