Critical magnetic fluctuations in strongly electron-correlated systems

Abstract

In this work, we use high-resolution neutron Triple-Axis and Spin-echo spectroscopy to study the critical properties of the strongly electron-correlated 4d square-lattice antiferromagnets Ca2RuO4 and Ca3Ru2O7, as well as of the heavy-fermion system CeCu5.8Au0.2 in vicinity and above the Néel-temperatures TN. We extract static and dynamical critical exponents to determine the spin dimensionalities and relevant anisotropies. We find that the critical behaviors of the single-layer compound Ca2RuO4 follow universal scaling laws that are compatible with predictions of the 2D-XY model. The bilayer compound Ca3Ru2O7 is only partly consistent with the 2D-XY theory and best described by the 3D-Ising model, which is likely a consequence of the intra-bilayer exchange interactions in combination with an orthorhombic single-ion anisotropy. For CeCu5.8Au0.2 we find signatures of a quantum-to-classical crossover in the dynamic scaling behavior.