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 demonstrate how layer specific in-plane magnetic anisotropy can be imprinted in amorphous multilayers. The anisotropy is obtained by growing the magnetic layers in the presence of an external field and the anisotropy direction can thereby be arbitrarily chosen for each of the magnetic layers. We used Co68Fe24Zr8 and Al70Zr30 layers as building blocks for demonstrating this effect. The imprinting is expected to be obtainable for a wide range of amorphous materials when grown at temperatures below the magnetic ordering temperature.
We present a method, combining optical transmission with electrical resistance, to study the hydrogen uptake in thin transition metal films. The change in optical transmission is used to determine the hydrogen concentration, while the change in resistance serves as an indicator for the ordering of hydrogen. We identify phase boundaries and regions of high and low orders as well as changes in the ordering temperature. As a demonstration of this approach we compare the hydrogen uptake of 50 and 10 nm single-crystal vanadium films. The ordered phase is found to be extended to higher temperatures in the thinner sample.
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.
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