[en] The series R₂PdSi₃ (R=rare earth), has been found to exhibit rich magnetic phenomena resulting from the interplay between RKKY interaction, crystal-electric field effects and geometric frustration. Except for the Ho₂PdSi₃ compound the second order crystal electric field parameter dominates the magneto-crystalline anisotropy. The Ho₂PdSi₃ compound which orders antiferromagnetically at T_N=7.7 K offers therefore the opportunity to study the influence of the higher order crystal electric field parameters. We performed inelastic neutron scattering experiments on a large Ho₂PdSi₃ single crystal in magnetic fields up to 13 T at the cold triple axis spectrometer (PANDA, FRM-II). In applied magnetic fields above the critical field for the transition into FM induced state, the crystal electric field levels undergo Zeeman splitting; and the energy shift varies from approx. 0.1 meV/T to 0.3 meV/T, implying the influence of the higher order crystal field parameters. In this contribution we present and discuss the results of the inelastic neutron scattering experiments and give a proposal for the crystal electric field level scheme

[en] We present first-time measurements of the Fermi surface and low-energy electronic structure of intermetallic compounds Gd₂PdSi₃ and Tb₂PdSi₃ by means of angle-resolved photoelectron spectroscopy (ARPES). We show that the Fermi surface in both compounds consists of an electron barrel at the Γ point surrounded by spindle-shaped electron pockets originating from the same band, with the band bottom of both features lying at 0.5 eV below the Fermi level. From the experimentally measured band structure, we estimate the momentum-dependent RKKY coupling strength and demonstrate that it is peaked at the 1/2Γ K wave vector. Comparison with neutron diffraction data from the same crystals shows perfect agreement of this vector with the propagation vector of the low-temperature in-plane magnetic order, thereby demonstrating the decisive role of the Fermi surface geometry in explaining the complex magnetically ordered ground state of ternary rare earth silicides.

[en] Thermal expansion and magnetostriction of single-crystalline R₂PdSi₃ (R = Ho, Dy) have been investigated by means of high-precision capacitance dilatometry and by specific heat studies. Pronounced anomalies in the uniaxial thermal expansion coefficients α_a and α_c and in the specific heat c_p mark the onset of long-range antiferromagnetic (AFM) order at T_N = 7.8(3) K (R = Ho) and T_N = 7.9(3) K (R = Dy). The different nature of the ground states in both materials is concluded from opposite signs of the thermal expansion anomalies, i.e., opposite uniaxial pressure dependencies. In both materials, there are Schottky-like entropy and anisotropic length changes which are attributed to crystal field effects and reorientation of the easy magnetic axes. The low-temperature magnetic phase diagrams and the magnetostriction data imply an interplay of single-ion effects and magnetic exchange interaction. Even small magnetic fields yield ferrimagnetic phases via yet unknown intermediate antiferromagnetic (Dy₂PdSi₃) and ferrimagnetic (Ho₂PdSi₃) phases. (author)