Emergent magnetic monopole dynamics in macroscopically degenerate artificial spin ice

Farhan, Alan; Saccone, Michael; Petersen, Charlotte F.; Dhuey, Scott; Chopdekar, Rajesh V.; Huang, Ying; Kent, Noah; Chen, Zuhuang; Alava, Mikko J.; Lippert, Thomas; Schöll, A.; Dijken, Sebastiaan van

doi:10.1126/sciadv.aav6380

Cited by 136 publications

(127 citation statements)

References 39 publications

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“…The pinch point Fig. 1 a is a type of singularity that is expected, and may be observed, in at least two types of system: firstly, dipolar systems, such as ferromagnets [1,2], and secondly, ice-rule systems, including hydrogen bonded ferroelectrics [3][4][5][6], water ice [7,8], spin ice [9][10][11][12][13][14], ionic ice [15,16], artificial spin ice [17][18][19], quantum spin ice [20][21][22] and antiferromagnetic spin liquids [23][24][25][26][27]. Such systems have the notable feature that they enter a highly correlated low-temperature state without any symmetry breaking.…”

Section: Introductionmentioning

confidence: 88%

Screening and the pinch point paradox in spin ice

Twengström

Henelius

Bramwell

2020

Phys. Rev. Research

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A pinch point singularity in the structure factor characterizes an important class of condensed matter that is a counterpoint to the paradigm of broken symmetry. This class includes water ice, charge ice and spin ice. Of these, dipolar spin ice affords the the pre-eminent model system because it has a well-established Hamiltonian, is simple enough to allow analytical theory and numerical simulation, and is well represented in experiment by Dy2Ti2O7 and Ho2Ti2O7. Nevertheless it is a considerable challenge to resolve the pinch points in simulation or experiment as they represent a very long range correlation. Here we present very high resolution simulations of the polarized neutron scattering structure factor of dipolar spin ice and new analytical theory of the pinch point profiles. We compare these with existing theory and experiment. We find that our simulations are consistent with theories that reveal the pinch points to be infinitely sharp, as a result of unscreened dipolar fields. However, neither simulation nor these theories are consistent with experiments, which instead is quantitatively captured by a theory that allows for screening of the dipolar fields and consequent strong broadening of the pinch points. This striking paradox is not easily resolved: broadening of the pinch points by random disorder seems to have been ruled out by existing theory, while deficiencies in the Hamiltonian description are not relevant. Intriguingly, we are left to consider the role of quantum fluctuations or the possibility of a fundamental correction to either the standard method of simulating dipolar systems, or the theory of polarized neutron scattering. More generally, our results may have relevance far beyond ice systems. For example, spin ice is a model Debye-Hückel (magnetic) electrolyte, so our basic observation that the screening length may diverge while the Debye length remains constant, may hint at a solution to the topical problem of 'underscreening' in concentrated ionic liquids.

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Section: Introductionmentioning

confidence: 88%

Screening and the pinch point paradox in spin ice

Twengström

Henelius

Bramwell

2020

Phys. Rev. Research

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“…This question might be addressed through computational studies [46] or improvements in the annealing procedure. Furthermore, it will be interesting to study the thermal stability of polaronic states with temperature dependent experiments [19,22]. The degree to which these charges are screened and their mobility may provide ideal conditions for new Debye-Hückel plasmas [19].…”

Section: Discussionmentioning

confidence: 99%

“…2(a)]. In an emergent magnetic charge picture [18,19,45,46], these vertices exhibit a zero magnetic charge at the vertex (Q = 0). Type III vertices break the ice rule, as three moments point into the vertex and one out or vice versa.…”

Section: A Energy Landscape and Micromagnetic Simulations Of Couplinmentioning

confidence: 99%

“…Similar to previous work on artificial frustrated systems [4,5,19,22,29], the prepared structures were kept at room temperature and in vacuum for several days. Then, the samples were transferred into the PEEM and cooled down 20-30 K below the temperature where thermally-induced moment fluctuations start to occur within the nanomagnets on the time scale of several seconds [19,22,29]. Cooling below the so-called blocking temperature (T B = 130 K in our system) ensures that configurations remain frozen during XMCD imaging after thermal annealing.…”

Section: B Thermal Annealing and Xmcd Imagingmentioning

confidence: 99%

“…Artificial spin ice systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], initially introduced as two-dimensional analogues to pyrochlore spin ice [17], enabled the direct visualization of the consequences of geometrical frustration using appropriate magnetic imaging techniques. In particular, the introduction of artificial spin ices that exhibit thermally induced moment fluctuations paved the way to explore the statistical physics of geometrical frustration [3][4][5][6], emergent magnetic monopoles and macroscopic spin ice degeneracy [18,19], in addition to first attempts in achieving artificial spin glasses [20]. Furthermore, this newly acquired possibility lead to a whole new line of research, where novel two-dimensional lattices comprising Ising-type nanomagnets are being designed, that would exhibit exotic emergent phenomena that go beyond spin ice physics.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dipolar Cairo lattice: Geometrical frustration and short-range correlations

Saccone

Hofhuis

Huang

et al. 2019

Phys. Rev. Materials

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We have studied low-energy configurations in two-dimensional arrays consisting of Ising-type dipolar coupled nanomagnets lithographically defined onto a two-dimensional Cairo lattice, thus dubbed the dipolar Cairo lattice. Employing synchrotron-based photoemission electron microscopy (PEEM), we perform real-space imaging of moment configurations achieved after thermal annealing. These states are then characterized in terms of vertex populations, spin-and emergent magnetic charge correlations, and a topology-enforced emergent ice rule. The results reveal a strong dominance of short-range correlations and the absence of long-range order, reflecting the high degree of geometrical spin frustration present in this example of an artificial frustrated spin system.

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Modal Frustration and Periodicity Breaking in Artificial Spin Ice

Puttock

Manzin

Neu

et al. 2020

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Switchable behaviors and writable defects in artificial spin ice have been extensively studied as nanoscale reconfigurable field sources for applications including neural networks and magnonics. Random-walk style chains of correlated excitations have been discussed as potential low-energy pathways for such applications, but writing controllable 1D pathways through lattices is generally challenging. We explore the modal behavior of a novel artificial spin ice design that generates magnetic uniaxial chains along a defined direction. In addition, non-Ising breakdown of the magnetization within constituent nanoislands is observed, with a rupture of magnetization periodicity is measured. Finally, locally perturbing the vertices in both traditional and non-Ising magnetic configurations produces both a "selective writing" capability, and a 2D network writability dependent on the fieldstrength of the perturbing field point-source, and its controlled motion. Such functionalities exhibit a route to highefficiency magnonic devices via novel lattice designs and controlled magnetic behaviors.

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Emergent magnetic monopole dynamics in macroscopically degenerate artificial spin ice

Abstract: We present direct, real-time observations of emergent magnetic monopole dynamics in highly frustrated artificial spin ice.

Cited by 136 publications

References 39 publications

Screening and the pinch point paradox in spin ice

Screening and the pinch point paradox in spin ice

Dipolar Cairo lattice: Geometrical frustration and short-range correlations

Modal Frustration and Periodicity Breaking in Artificial Spin Ice

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