Interplay between Kondo-like behavior and short-range antiferromagnetism in EuCu_2Si_2 single crystals

摘要

The static and dynamic magnetic properties, electrical resistivity, specific heat, and magnetoresistance have been studied in EuCu_2Si_2 single crystals grown by a floating zone method. The magnetic susceptibility exhibits a considerable anisotropy and a steep rise below 10 K for external fields parallel to the c axis but with no evident magnetic, ordering in the temperature range of 2-350 K. The data imply a gradual change in the Eu valence as a function of temperature. Electron spin resonance (ESR) measurements reveal a sizeable fraction of stable Eu~(2+) magnetic moments that interact with conduction electrons and develop quasistatic antiferromag-netic correlations on the ESR timescale. The electrical resistivity and specific heat demonstrate the presence of spin fluctuations and Kondo-like behavior, which apparently competes with the antiferromagnetic order. The analysis of experimental data enables to conclude that the remarkable diversity of the physical properties of EuCu_2Si_2 results from the variation of lattice parameters as well as of local crystal chemistry as a consequence of the particular preparation route employed for the growth of single crystals and polycrystals.