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Center for Nonlinear Studies |
The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Investigating artificial magnetic nano-assemblies allows an inside in these fundamental phenomena and the use of thermally active materials enables us to explore the thermodynamic behavior of such artificial assemblies of mesoscopic spins. By the means of nano-lithography we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks and design a two-dimensional model system to our needs. We report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrate that these can serve as an ideal playground for the studies of collective dynamics and relaxations. Focusing on lattices with different building blocks such as the Shakti lattice, opens up interesting prospects in the thermodynamic picture of nano-magnetic systems. Building blocks with differently sized elements have different thermal active temperature regions. The influence of these energetic differences is investigated by local measurements of the magnetic orientation of the single elements in the Shakti lattice, using Photoemission Electron Microscopy (PEEM) employing the X-ray Magnetic Circular Dichroism (XMCD) at a Synchrotron radiation source (ALS Berkley). Comparisons between the Shakti lattice and the modified Shakti lattice, a lattice with the same lateral arrangement of building blocks but with only one size of elements in these blocks, reveals relaxation dynamics in these lattices which indicate an excitation translation into weaker coupled regions. These excitation translations into weaker sides of the lattice are represented by out of equilibrium vertex populations in these areas.
Host: Cristiano Nisoli