Magnetic excitations of Er₂PdSi₃ studied by inelastic neutron scattering in fields up to 12 T

The series R₂PdSi₃ (R = heavy rare earth) has been found to exhibit rich magnetic phase diagrams with a large variety of magnetic states. This complex magnetic behavior results from the interplay between RKKY interaction, magneto-crystalline anisotropy based on crystalline-electric field (CEF) effects and geometric frustration due to the AlB₂ derived hexagonal crystal structure. Within the series the Er₂PdSi ₃ compound has been found to exhibit in zero field a simple CEF excitation spectrum with just one strong transition at 3.5 meV from the ground state to the first excited state. Neutron spectroscopy in magnetic fields up to 12 T has been performed on the cold-triple axis spectrometer PANDA at FRM II. In this study two transitions within the 3.5 meV excitation could be resolved showing a linear dependency in applied magnetic fields with an almost identical slope of μ_Bg_L for fields above 2 T. The results can be explained in a picture of two slightly different sets of CEF parameters for two inequivalent Er³⁺ sites due the crystallographic superstructure observed in all single crystals of type R₂PdSi₃.