Browsing by Author "Scholl, Andreas"
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Other contribution(2017-12-01) Farhan, Alan; Petersen, Charlotte; Dhuey, Scott; Anghinolfi, Luca; Qin, QiHang; Saccone, Michael; Velten, Sven; Gliga, Sebastian; Mellado, Paula; Alava, Mikko; Scholl, Andreas; van Dijken, SebastiaanThe original version of this article contained an error in the legend to Figure 4. The yellow scale bar should have been defined as '∼600 nm', not '∼600 μm'. This has now been corrected in both the PDF and HTML versions of the article. - Dipolar Cairo lattice: Geometrical frustration and short-range correlations
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-10-07) Saccone, Michael; Hofhuis, Kevin; Huang, Yen Lin; Dhuey, Scott; Chen, Zuhuang; Scholl, Andreas; Chopdekar, Rajesh V.; Van Dijken, Sebastiaan; Farhan, AlanWe 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. - Emergent magnetic monopole dynamics in macroscopically degenerate artificial spin ice
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-02-08) Farhan, Alan; Saccone, Michael; Petersen, Charlotte F.; Dhuey, Scott; Chopdekar, Rajesh V.; Huang, Yen Lin; Kent, Noah; Chen, Zuhuang; Alava, Mikko J.; Lippert, Thomas; Scholl, Andreas; van Dijken, SebastiaanMagnetic monopoles, proposed as elementary particles that act as isolated magnetic south and north poles, have long attracted research interest as magnetic analogs to electric charge. In solid-state physics, a classical analog to these elusive particles has emerged as topological excitations within pyrochlore spin ice systems. We present the first real-time imaging of emergent magnetic monopole motion in a macroscopically degenerate artificial spin ice system consisting of thermally activated Ising-type nanomagnets lithographically arranged onto a pre-etched silicon substrate. A real-space characterization of emergent magnetic monopoles within the framework of Debye-Hückel theory is performed, providing visual evidence that these topological defects act like a plasma of Coulomb-type magnetic charges. In contrast to vertex defects in a purely two-dimensional artificial square ice, 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. - Geometrical Frustration and Planar Triangular Antiferromagnetism in Quasi-Three-Dimensional Artificial Spin Architecture
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-12-30) Farhan, Alan; Saccone, Michael; Petersen, Charlotte; Dhuey, Scott; Hofhuis, Kevin; Mansell, Rhodri; Chopdekar, Rajesh V.; Scholl, Andreas; Lippert, Thomas; van Dijken, SebastiaanWe present a realization of highly frustrated planar triangular antiferromagnetism achieved in a quasi-three-dimensional artificial spin system consisting of monodomain Ising-type nanomagnets lithographically arranged onto a deep-etched silicon substrate. We demonstrate how the three-dimensional spin architecture results in the first direct observation of long-range ordered planar triangular antiferromagnetism, in addition to a highly disordered phase with short-range correlations, once competing interactions are perfectly tuned. Our work demonstrates how escaping two-dimensional restrictions can lead to new types of magnetically frustrated metamaterials. - Nanoscale control of competing interactions and geometrical frustration in a dipolar trident lattice
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-12-01) Farhan, Alan; Petersen, Charlotte F.; Dhuey, Scott; Anghinolfi, Luca; Qin, Qi Hang; Saccone, Michael; Velten, Sven; Wuth, Clemens; Gliga, Sebastian; Mellado, Paula; Alava, Mikko J.; Scholl, Andreas; Van Dijken, SebastiaanGeometrical frustration occurs when entities in a system, subject to given lattice constraints, are hindered to simultaneously minimize their local interactions. In magnetism, systems incorporating geometrical frustration are fascinating, as their behavior is not only hard to predict, but also leads to the emergence of exotic states of matter. Here, we provide a first look into an artificial frustrated system, the dipolar trident lattice, where the balance of competing interactions between nearest-neighbor magnetic moments can be directly controlled, thus allowing versatile tuning of geometrical frustration and manipulation of ground state configurations. Our findings not only provide the basis for future studies on the low-temperature physics of the dipolar trident lattice, but also demonstrate how this frustration-by-design concept can deliver magnetically frustrated metamaterials. - Thermodynamics of emergent magnetic charge screening in artificial spin ice
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-09-01) Farhan, Alan; Scholl, Andreas; Petersen, Charlotte F.; Anghinolfi, Luca; Wuth, Clemens; Dhuey, Scott; Chopdekar, Rajesh V.; Mellado, Paula; Alava, Mikko J.; Van Dijken, SebastiaanElectric charge screening is a fundamental principle governing the behaviour in a variety of systems in nature. Through reconfiguration of the local environment, the Coulomb attraction between electric charges is decreased, leading, for example, to the creation of polaron states in solids or hydration shells around proteins in water. Here, we directly visualize the real-time creation and decay of screened magnetic charge configurations in a two-dimensional artificial spin ice system, the dipolar dice lattice. By comparing the temperature dependent occurrence of screened and unscreened emergent magnetic charge defects, we determine that screened magnetic charges are indeed a result of local energy reduction and appear as a transient minimum energy state before the system relaxes towards the predicted ground state. These results highlight the important role of emergent magnetic charges in artificial spin ice, giving rise to screened charge excitations and the emergence of exotic low-temperature configurations. - Towards artificial Ising spin glasses: Thermal ordering in randomized arrays of Ising-type nanomagnets
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-06-03) Saccone, Michael; Scholl, Andreas; Velten, Sven; Dhuey, Scott; Hofhuis, Kevin; Wuth, Clemens; Huang, Yen-Lin; Chen, Zuhuang; Chopdekar, Rajesh; Farhan, AlanWe explore the thermodynamics in two-dimensional arrays consisting of Ising-type nanomagnets lithographically arranged onto random sites and angular orientations. Introducing these basic spin-glass ingredients, we study the characteristic features of the low-energy states achieved, following thermal-annealing protocols. From direct visualization of real-time dynamics, we record relaxation timescales together with magnetic susceptibility variations over temperature, revealing trends towards short-range order as randomness is increased, but falling short of pure spin-glass behavior. Our work provides a route towards the realization of artificial Ising spin-glass systems. - Tuning magnetic ordering in a dipolar square-kite tessellation
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-02-26) Petersen, Charlotte F.; Farhan, Alan; Dhuey, Scott; Chen, Zuhuang; Alava, Mikko J.; Scholl, Andreas; Van Dijken, SebastiaanThe potential application of artificial spin ice in magnetic nanodevices provides a strong drive to investigate different lattice geometries. Here, we combine components of a recently investigated artificial spin ratchet with components of the prototypical square lattice to form a geometrically frustrated artificial spin ice system where Ising-type nanomagnets are arranged onto a two-dimensional square-kite lattice. Using synchrotron-based photoemission electron microscopy, we explore moment configurations achieved in this lattice geometry. Following thermal annealing, we image how a variation of the relevant lattice parameter affects magnetic ordering in four-island squares and four-island vertices during cooling through the Blocking temperature. Depending on lattice spacing, both nearly uniform and disordered spin configurations are accessible in our samples. We show that the relative energies of the building blocks of the system, which are typically used to classify lattice configurations, are not predictive of the low energy states adopted by the experimental system. To understand magnetic ordering in the square-kite lattice, longer range interactions must be considered.