Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature-dependent magnetization in different principal directions and comparing it with simulations of idealized statistical mechanical models. Our results confirm a dynamical premelting 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 the real thermal dynamics of artificial spins over an extended temperature range.Geometric frustration is observed in many physical systems. A textbook example is the frustration of proton interactions in water ice, giving rise to proton disorder, as revealed by the pioneering experimental work of Giauque and Stout [1] and the theoretical interpretation by Pauling [2]. Frustration in antiferromagnets analogous to the ice model was predicted
We have fabricated ultra-thin disc shaped islands wherein shape anisotropy confines the moment to the island plane, creating XY-like superspins. At low temperatures, the superspins are blocked, and, as the temperature is increased, they undergo a transition into a superparamagnetic state. The onset of this dynamic superspin state scales with the diameter of the islands, and it persists up to a temperature governed by the intrinsic ordering temperature of the island material defining a range in temperature in which dynamic behavior of the magnetic islands can be obtained.
The structural, optical and electronic properties of the copper nitride (Cu 3 N) bulk structure under pressure have been studied by performing accurate total energy calculations in the framework of density functional theory using the full-potential linearized augmented plane wave method. Perdew-Burke-Ernzerhof and modified Becke-Johnson parameterizations of the generalized gradient approximation were employed to obtain the structural and electronic properties of Cu 3 N. The most stable crystal structure of the Cu 3 N compound was found to be cubic anti-ReO 3 at ambient pressure. Moreover, the calculation of the enthalpy of different crystal structures of Cu 3 N for different pressures indicates that the anti-ReO 3 cubic phase undergoes a structural phase transition for pressures higher than 30 GPa. The study of the elastic constants of the anti-ReO 3 cubic phase confirms that Cu 3 N is mechanically stable under hydrostatic pressures up to 30 GPa. Moreover, with the application of pressure, the C 44 elastic constant, shear module and Debye temperature deviate from linear behavior at 10 GPa. An electronic study shows that there is an electronic-type phase transition from semiconductor to metal between 5 and 10 GPa and metal to semi-metal between 20 and 30 GPa applied pressures. Cu 3 N is an indirect band gap semiconductor with a value of 0.56 eV.
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