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Realizing Colloidal Artificial Ice on Arrays of Optical Traps  [PDF]
A. Libal,C. Reichhardt,C. J. Olson Reichhardt
Physics , 2006, DOI: 10.1103/PhysRevLett.97.228302
Abstract: We demonstrate how a colloidal version of artificial ice can be realized on optical trap lattices. Using numerical simulations, we show that this system obeys the ice rules and that for strong colloid-colloid interactions, an ordered ground state appears. We show that the ice rule ordering can occur for systems with as few as twenty-four traps and that the ordering transition can be observed at constant temperature by varying the barrier strength of the traps.
Dynamics of colloidal particles in ice  [PDF]
Melissa Spannuth,S. G. J. Mochrie,S. S. L. Peppin,J. S. Wettlaufer
Physics , 2010, DOI: 10.1063/1.3665927
Abstract: We use X-ray Photon Correlation Spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high-particle-density, where some of the colloids were forced into contact and formed disordered aggregates. We find that the particles in these high density regions underwent ballistic motion coupled with both stretched and compressed exponential decays of the intensity autocorrelation function, and that the particles' characteristic velocity increased with temperature. We explain this behavior in terms of ice grain boundary migration.
Doped Colloidal ZnO Nanocrystals
Yizheng Jin,Yuping Ren,MoTao Cao,Zhizhen Ye
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/985326
Abstract: Colloidal ZnO nanocrystals are promising for a wide range of applications due to the combination of unique multifunctional nature and remarkable solution processability. Doping is an effective approach of enhancing the properties of colloidal ZnO nanocrystals in well-controlled manners. In this paper, we analyzed two synthetic strategies for the doped colloidal ZnO nanocrystals, emphasizing our understanding on the critical factors associated with the high temperature and nonaqueous approach. Latest advances of three topics, bandgap engineering, n-type doping, and dilute magnetic semiconductors related to doped ZnO nanocrystals were discussed to reveal the effects of dopants on the properties of the nanocrystalline materials.
Direct entropy determination and application to artificial spin ice  [PDF]
Paul E. Lammert,Xianglin Ki,Jie Li,Cristiano Nisoli,David M. Garand,Vincent H. Crespi,Peter Schiffer
Physics , 2012, DOI: 10.1038/nphys1728
Abstract: From thermodynamic origins, the concept of entropy has expanded to a range of statistical measures of uncertainty, which may still be thermodynamically significant. However, laboratory measurements of entropy continue to rely on direct measurements of heat. New technologies that can map out myriads of microscopic degrees of freedom suggest direct determination of configurational entropy by counting in systems where it is thermodynamically inaccessible, such as granular and colloidal materials, proteins and lithographically fabricated nanometre-scale arrays. Here, we demonstrate a conditional-probability technique to calculate entropy densities of translation-invariant states on lattices using limited configuration data on small clusters, and apply it to arrays of interacting nanometre-scale magnetic islands (artificial spin ice). Models for statistically disordered systems can be assessed by applying the method to relative entropy densities. For artificial spin ice, this analysis shows that nearest-neighbour correlations drive longer-range ones.
Multi-Step Ordering in Kagome and Square Artificial Spin Ice  [PDF]
C. J. Olson Reichhardt,A. Libal,C. Reichhardt
Physics , 2011, DOI: 10.1088/1367-2630/14/2/025006
Abstract: We show that in colloidal models of artificial kagome and modified square ice systems, a variety of ordering and disordering regimes occur as a function of biasing field, temperature, and colloid-colloid interaction strength, including ordered monopole crystals, biased ice rule states, thermally induced ice rule ground states, biased triple states, and disordered states. We describe the lattice geometries and biasing field protocols that create the different states and explain the formation of the states in terms of sublattice switching thresholds. For a system prepared in a monopole lattice state, we show that a sequence of different orderings occurs for increasing temperature. Our results also explain several features observed in nanomagnetic artificial ice systems under an applied field.
Melting artificial spin ice  [PDF]
Vassilios Kapaklis,Unnar B. Arnalds,Adam Harman-Clarke,Evangelos Th. Papaioannou,Masoud Karimipour,Panagiotis Korelis,Andrea Taroni,Peter C. W. Holdsworth,Steven T. Bramwell,Bj?rgvin Hj?rvarsson
Physics , 2011, DOI: 10.1088/1367-2630/14/3/035009
Abstract: Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Despite much progress in elucidating the properties of such arrays, the `spins' in the systems studied so far have no thermal dynamics as the kinetic constraints are too high. Here we address this problem by using a material with an ordering temperature near room temperature. By measuring the temperature dependent magnetization in different principal directions, and comparing with simulations of idealized statistical mechanical models, we confirm a dynamical `pre-melting' of the artificial spin ice structure at a temperature well below the intrinsic ordering temperature of the island material. We thus create a spin ice array that has real thermal dynamics of the artificial spins over an extended temperature range.
Viscoelasticity of colloidal polycrystals doped with impurities  [PDF]
Ameur Louhichi,Elisa Tamborini,Julian Oberdisse,Luca Cipelletti,Laurence Ramos
Physics , 2015, DOI: 10.1103/PhysRevE.92.032307
Abstract: We investigate how the microstructure of a colloidal polycrystal influences its linear viscoelasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and does not vary neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure.
Reducing Disorder in Artificial Kagome Ice  [PDF]
Stephen A. Daunheimer,Olga Petrova,Oleg Tchernyshyov,John Cumings
Physics , 2011, DOI: 10.1103/PhysRevLett.107.167201
Abstract: Artificial spin ice has become a valuable tool for understanding magnetic interactions on a microscopic level. The strength in the approach lies in the ability of a synthetic array of nanoscale magnets to mimic crystalline materials, composed of atomic magnetic moments. Unfortunately, these nanoscale magnets, patterned from metal alloys, can show substantial variation in relevant quantities such as coercive field, with deviations up to 6%. By carefully studying the reversal process of artificial kagome ice, we can directly measure the distribution of coercivities, and by switching from disconnected islands to a connected structure, we find that the coercivity distribution can achieve a deviation of only 3.3%. These narrow deviations should allow the observation of behavior that mimics canonical spin-ice materials more closely.
Can secondary nucleation exist in ice banding of freezing colloidal suspensions?  [PDF]
Jiaxue You,Jincheng Wang,Lilin Wang,Zhijun Wang,Xiaobing Hu,Junjie Li,Xin Lin
Physics , 2015,
Abstract: The formation mechanism of ice banding in the system of freezing colloidal suspensions, which is of significance in frost heaving, ice-templating porous materials and biological materials, still remains a mystery. Recently, the theory of secondary nucleation and growth of ice has been proposed to explain the emergence of a new ice lens. However, this theory has not been quantitatively examined. Here, we quantitatively measured the initial interfacial undercooling of a new ice lens and the nucleation undercoolings of suspensions. We found that the interfacial undercooling can not satisfy the nucleation undercooling of ice and hence disprove the secondary nucleation mechanism for ice banding.
Direct observation of the ice rule in artificial kagome spin ice  [PDF]
Yi Qi,T. Brintlinger,John Cumings
Physics , 2008, DOI: 10.1103/PhysRevB.77.094418
Abstract: Recently, significant interest has emerged in fabricated systems that mimic the behavior of geometrically-frustrated materials. We present the full realization of such an artificial spin ice system on a two-dimensional kagome lattice and demonstrate rigid adherence to the local ice rule by directly counting individual pseudo-spins. The resulting spin configurations show not only local ice rules and long-range disorder, but also correlations consistent with spin ice Monte Carlo calculations. Our results suggest that dipolar corrections are significant in this system, as in pyrochlore spin ice, and they open a door to further studies of frustration in general.
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