[en] 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 Er₂PdSi₃ 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.

No abstract available

[en] Due to the interplay between RKKY exchange interaction, crystalline-electric field (CEF) effects and geometric frustration due to the AlB₂-derived hexagonal crystal structure, the study of R₂PdSi₃ (R = rare earth) has been found to be a challenging field in rare earth magnetism. In this contribution we present the results of neutron diffraction experiments on a Ho₂PdSi₃ single crystal in the magnetically ordered state at T = 1.6 K. The compound orders antiferromagnetically in the basal plane with the propagation vector τ = (1/7-δ, 2δ, 0) where δ ∼ 0.01 r.l.u. In magnetic fields applied along the (1overline 10) magnetic hard axis, the structure persists up to the highest measured field of 5 T. The dependence of the intensities as a function of field suggests that the τ structure is a single-k multi-domain structure.

[en] R₂PdSi₃ compounds have been found to exhibit rich magnetic phenomena arising from the interplay between RKKY interaction, crystal electric field effects and geometric frustration due to the derived hexagonal AlB₂ structure. The observed crystallographic superstructure further complicates the CEF level scheme. Inelastic neutron scattering measurements on single crystals of Tm₂PdSi₃ and Er₂PdSi₃ have been performed at the cold triple axis spectrometer PANDA in FRM-II. Both compounds order antiferromagnetically at T_N=7 K and 2.1 K respectively; Er₂PdSi₃ undergoes a second phase transition at T₂=2 K. Several low lying CEF excitations (below 10 meV) were observed. The intensity of the lowest excitation show strong directional dependence (in HK0 plane for Er₂PdSi₃ and in HHL plane for Tm₂PdSi₃), from which the details of the transitional matrix could be deduced. Measurements in magnetic fields up to 13 T show Zeeman splitting of the CEF excitations. In this contribution we present and discuss the results of the inelastic neutron scattering experiments and try to entangle the CEF level scheme.

No abstract available

[en] We present results of neutron diffraction experiments on a Ho₂PdSi₃ single crystal in the magnetically ordered state at T = 1.5 K for magnetic fields applied in the easy (0, 0, L) direction. Moderate fields of less than 0.8 T are sufficient to wipe out the antiferromagnetic order in the basal plane of the AlB₂-type hexagonal lattice structure. Concurrently strong magnetic reflections along the (0, 0, L) direction develop with increasing fields that are closely related to the nuclear superstructure reflections found in the single crystal at all temperatures. The field dependence of the intensity of the these reflections is rather unusual: after a maximum at 0.6 T and a shallow minimum at 2 T a further increase of intensity for fields up to 5 T is observed. A phase transition into a field induced, saturated ferromagnetic state is expected only at very high fields (> 13 T) as inferred from magnetization data. For the origin of the high field magnetic structure two models are proposed and the corresponding model calculations are compared to our experimental results. Furthermore, the experimental data in low fields (< 0.8 T) are used to clarify the hitherto unsolved zero-field magnetic structure of Ho₂PdSi₃. The relevance of our findings with respect to other members of the R₂PdSi₃ series (R = Tb, Er, Tm and others) is emphasized.

[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] Tb₂PdSi₃ crystallises in an AlB₂ derived hexagonal structure (spacegroup P 6/mmm) yielding a latent geometric frustration for the magnetic Tb³⁺ ions. The anisotropy of the crystal electric field leads to a magnetic easy basal plane with six possible moment directions. The RKKY interaction gives rise to an antiferromagnetic transition at T_N=23 K. To clarify the microscopic nature of the rich magnetic phase diagram we performed neutron scattering experiments in external magnetic fields up to μ0 H=6.5 T along the (100) direction. In zero field we observe an antiferromagnetic long-range ordered (LR) structure with a magnetic unit cell doubled in the basal plane with respect to the chemical unit cell and a (0 0 1/16) propagation along the hexagonal axis. Below 8 K an additional antiferromagnetic short range ordered (SR) structure with a wave vector (0.16 0.16 0.06) appears. The LR propagation changes through two intermediate phases to (0 0 1/4) in the field range 0.1-3.0 T. The SR structure seems decoupled from the LR structure and becomes itself long-range ordered around 1.5 T with a propagation (0.13 0.13 0.1) which is further modified to (1/6 1/6 1/4) at fields above 3 T

[en] The series R₂PdSi₃ (R=heavy rare earth) crystallize in a special variant of the hexagonal AlB₂ structure where the Pd and Si ions order on the B-sites resulting in a crystallographic superstructure. The rare earth ions occupy the Al-sites on a triangular and therefore geometrically frustrated lattice. In zero field the R₂PdSi₃ order in a rich variety of antiferromagnetic structures. The diversity reflects the influence of the magneto-crystalline anisotropy based on crystal-electric field effect. The geometric frustration can be lifted by the application of a magnetic field. Apparently this leads to a more generalized behavior as suggested by ac-susceptibility measurements. In our contribution we will present and combine results from field dependent ac-susceptibility measurements and magnetic neutron diffraction on single crystalline R₂PdSi₃ for selected samples. The existence of a general high-field magnetic structure and a generic behavior for all R₂PdSi₃ will be discussed. Its connection to a special variant of the AlB₂ crystallographic structure will be emphasized.