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Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals

Published

Author(s)

Barry Farmer, Vinayak Bhat, Andrew L. Balk, Eric Teipel, Nathan Smith, John Unguris, D.J. Keavney, Todd Hastings, L .E. De Long

Abstract

Quasicrystals are rarely found in nature and are difficult to grow in the laboratory, but exhibit unique physical properties resulting from their signature long-range structural order without periodic translational symmetry. Magnetic interactions in quasicrystals are not well understood, and even the existence of long-range magnetic order in these materials is controversial. Fortunately, advances in nanofabrication permit ferromagnetic thin films to be patterned into "artificial quasicrystals" whose complex magnetic reversal and dynamics can now be systematically controlled via tiling design. The magnetization and domain walls of this new class of metamaterials are constrained by sub-micron patterning, so it is essential to experimentally characterize their mesoscopic magnetic textures. We therefore have acquired the first direct, two-dimensional images of the magnetization of permalloy films patterned into Penrose P2 tilings (P2T) using scanning electron microscopy with polarization analysis (SEMPA)7. Our SEMPA images demonstrate P2T behave as geometrically frustrated networks of narrow ferromagnetic film segments having near-uniform, bipolar (Ising-like) magnetization, similar to artificial spin ices (ASI). However, most ASI studied to date are periodic arrays of identical Ising segments with symmetric vertices of low coordination that obey spin ice rules and resist full equilibration into a magnetically ordered ground state. We find the unique aperiodic translational symmetry and diverse vertex coordination of multiply-connected P2T induce a more complex spin-ice behavior driven by exchange interactions in vertex domain walls (DW), which differs markedly from the behavior of disconnected ASI governed only by dipolar interactions. Our SEMPA images of as-grown P2T reveal magnetically ordered sublattices that function as low-energy building blocks for the emergent ground state of a quasicrystal of classical Ising spins. *ABSTRCT TOO LONG FOR FORM*
Citation
Physical Review B
Volume
93
Issue
13

Keywords

Quasicrystals, artificial spin ice, SEMPA, magnetic imaging

Citation

Farmer, B. , Bhat, V. , Balk, A. , Teipel, E. , Smith, N. , Unguris, J. , Keavney, D. , Hastings, T. and De Long, L. (2016), Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals, Physical Review B, [online], https://doi.org/10.1103/PhysRevB.93.134428, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916358 (Accessed February 21, 2024)
Created April 24, 2016, Updated October 12, 2021