The Polish synchrotron radiation facility, Solaris, is being built in Krakow. The project is strongly linked to the MAX-IV project and the 1.5 GeV storage ring. An overview will be given of activities and of the control system and will outline the similarities and differences between the two machines.

The gamma-gamma perturbed angular correlation technique (PAC) using Ru-99 was applied to investigate the orbital ordering of Ru 4d electrons in Ca2RuO4. It was confirmed that the ferro-orbital ordering characterized by the double occupation of d(xy) orbitals at every Ru ion is realized in the stoichiometric Ca2RuO4. A strong temperature dependence of the quadrupole interaction below the metal-insulator transition around 360 K reflects variation in the occupation of crystal field orbitals enhanced by very pronounced change in the lattice parameters. Temperature dependence of the hyperfine magnetic field H-hf at the Ru site shows very steep increase just below the ordering temperature, which could suggest a two-dimensional character of the magnetic ordering in Ca2RuO4.

The $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ perturbed angular correlation technique (PAC) using $^{99}\text{R}\text{u}$ was applied to investigate the orbital ordering of $\text{Ru}\text{ }4d$ electrons in ${\text{Ca}}_{2}{\text{RuO}}_{4}$. It was confirmed that the ferro-orbital ordering characterized by the double occupation of ${d}_{xy}$ orbitals at every Ru ion is realized in the stoichiometric ${\text{Ca}}_{2}{\text{RuO}}_{4}$. A strong temperature dependence of the quadrupole interaction below the metal-insulator transition around 360 K reflects variation in the occupation of crystal field orbitals enhanced by very pronounced change in the lattice parameters. Temperature dependence of the hyperfine magnetic field ${H}_{\text{hf}}$ at the Ru site shows very steep increase just below the ordering temperature, which could suggest a two-dimensional character of the magnetic ordering in ${\text{Ca}}_{2}{\text{RuO}}_{4}$.

Ru99 Mössbauer spectroscopy (ME) and Ru99γ– γ perturbed angular correlation measurements were applied to investigate magnetic properties of SrRuO3 and CaRuO3 in the wide temperature range. In case of ferromagnetic SrRuO3, the hyperfine magnetic field at Ru site Hhf0=327(2) kOe was determined and compared with the previous results obtained by ME and NMR methods. Possible contributions to the Hhf in SrRuO3 and its temperature dependence are discussed. For CaRuO3, strong evidence of lack of any freezing of Ru magnetic moments down to 1.8 K is given, which excludes any spin-glass or short-range order. A possible origin of the observed magnetization irreversibility is qualitatively discussed.

We have examined the magnetic properties of the heavy electron compounds YbAgGe and YbPtIn by 170Yb Mössbauer spectroscopy down to 0.1 K, and the crystal field properties of YbAgGe by Perturbed Angular Correlations (PAC) measurements up to 900 K. In YbAgGe, we show that each of the two magnetically ordered phases below 0.8 K involves a specific incommensurate modulation of the Yb moment. An analysis of existing low temperature specific heat data suggests the persistence of fluctuations of the correlated Yb spins down to 0.1 K. The PAC data allow to discriminate among proposed Yb3+ crystal field level schemes. In YbPtIn, we show that the low temperature magnetic order phase has an antiferro-para structure, where zero moment Yb ions coexist with large moment ones, and that a 90° moment reorientation occurs at 1.4 K.

PAC measurements were performed for 111In in LaAg6In6, PrAg6In6 and NdAg6In6. It appears that the probe atom occupy three available sites in the crystal lattice with quite a similar probability. There is a small preference for In atoms to occupy a selected lattice site which is not the same in different compounds.

Using 170Yb and 155Gd Mössbauer measurements down to ∼ 0.03 K, we have examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and 172Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur at 17 K in Yb2Mo2O7 and at 75 K in Gd2Mo2O7 and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations at 0.027 K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic.

In the garnet-structure compound Yb3Ga5O12, the Yb3+ ions (ground-state effective spin S' = 1/2) are situated on two interpenetrating corner-sharing triangular sublattices such that frustrated magnetic interactions are possible. Previous specific heat measurements have evidenced the development of short-range magnetic correlations below similar to0.5 K and a lambda-transition at 0.054 K (Filippi et at 1980 J. Phys. C: Solid State Physics 13 1277). From Yb-170 Mossbauer spectroscopy measurements down to 36 mK, we find that there is no static magnetic order at temperatures below that of the lambda-transition. Below similar to0.3 K, the fluctuation frequency of the short-range correlated Yb3+ moments progressively slows down and, as T --> 0, it tends to a quasi-saturated value of 3 x 10(9) s(-1). We also examined the Yb3+ paramagnetic relaxation rates up to 300 K using Yb-172 perturbed angular correlation measurements: they evidence phonon-driven processes.

Using neutron diffraction, 170Yb Mössbauer and muon spin relaxation spectroscopies, we have examined the pyrochlore Yb2Ti2O7, where the Yb3+S' = 1/2 ground state has planar anisotropy. Below approximately 0.24 K, the temperature of the known specific-heat lambda transition, there is no long range magnetic order. We show that the transition corresponds to a first-order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate, in the GHz range, follows a thermal excitation law, whereas below, the rate, in the MHz range, is temperature independent, indicative of a quantum fluctuation regime.

In the pyrochlore-structure compounds R2Ti2O7, the rare-earth (R) sublattice forms a network of corner-sharing tetrahedra such that the magnetic interactions may be geometrically frustrated. The low-temperature magnetic properties of these compounds are fashioned both by the frustration and by the intrinsic properties of the rare earth, that is, by the degeneracy and anisotropy of the rare-earth crystal-field ground state and by the nature, size and strength of the inter-ionic magnetic coupling. For Yb2Ti2O7, we combine 170Yb Mössbauer spectroscopy, 172Yb perturbed angular correlation, magnetization and susceptibility measurements to establish the Yb3+ crystal-field level scheme and to show that the crystal-field ground state is a well isolated Kramers doublet having a planar anisotropy. The main contribution to the Yb3+-Yb3+ coupling is the exchange interaction which is ferromagnetic. We describe the frustration-related low temperature (<1 K) properties of Yb2Ti2O7 in a separate publication.

The radioactive decay of Lu-172 --> Yb-172 appears to be suitable for time-differential perturbed angular correlation measurements of quadrupole interaction. The technique was applied to study various phenomena in three compounds: Yb3S4, YbPO4, Yb2Co3Ga9. We were able to distinguish between Yb2+ and Yb3+ ions occupying different positions in the crystal lattice of Yb3S4. Crystal electric field parameters reproduced the temperature dependence of the quadrupole interaction of Yb in YbPO4. Finally, the influence of hybridization on the 4f quadrupole moment in Yb2Co3Ga9 is evidenced.

${\mathrm{Yb}}_{2}{\mathrm{Co}}_{3}{\mathrm{Al}}_{9}$ and ${\mathrm{Yb}}_{2}{\mathrm{Co}}_{3}{\mathrm{Ga}}_{9}$ are isostructural compounds with an orthorhombic crystal structure having a unique Yb site. The Yb ions are in a trivalent state in ${\mathrm{Yb}}_{2}{\mathrm{Co}}_{3}{\mathrm{Al}}_{9}$ and order magnetically near 1.2 K, inferred both from low-temperature heat capacity and ${}^{170}\mathrm{Yb}$ M\"ossbauer spectroscopy measurements. A well-resolved hyperfine field split spectrum at 0.06 K yields a spontaneous moment of $0.93{\ensuremath{\mu}}_{B}/\mathrm{Yb}.$ From the thermal variation of the $4f$ specific heat and of the $4f$ quadrupolar moment in the paramagnetic phase, we could determine the energies of the four crystal-field states of ${\mathrm{Yb}}^{3+},$ and we find that the overall splitting is about 180 K. By contrast, the $4f$ electronic state of Yb ions in ${\mathrm{Yb}}_{2}{\mathrm{Co}}_{3}{\mathrm{Ga}}_{9}$ is strongly hybridized with the conduction-electron band states, with valency close to 2.9 as determined by ${L}_{\mathrm{III}}$-edge x-ray-absorption measurements. The Pauli paramagnetic ground state, with $\ensuremath{\chi}\ensuremath{\simeq}12.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\mathrm{emu}$ $(\mathrm{Yb}\mathrm{}\mathrm{mol}{)}^{\ensuremath{-}1}$ and the thermal variation of the susceptibility on the one hand, the Sommerfeld coefficient $\ensuremath{\gamma}\ensuremath{\simeq}120\mathrm{mJ}$ $(\mathrm{Yb}\mathrm{}\mathrm{mol}{)}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}2}$ and the thermal variation of the $4f$ heat capacity on the other hand, are quantitatively well explained in the Coqblin-Schrieffer limit of the $J=\frac{7}{2}$ Kondo impurity, with a characteristic hybridization (or Kondo) scale ${T}_{0}=235\mathrm{K}.$ From the ${}^{170}\mathrm{Yb}$ M\"ossbauer spectra recorded up to 77 K and ${}^{172}\mathrm{Yb}$ perturbed angular correlation data recorded up to 1000 K, we find that the thermal variation of the $4f$ quadrupolar moment ${Q}^{4f}(T)$ in ${\mathrm{Yb}}_{2}{\mathrm{Co}}_{3}{\mathrm{Ga}}_{9}$ scales with the magnetic susceptibility $\ensuremath{\chi}(T),$ as predicted by theory to occur in the case the Kondo scale is larger than the crystal-field splittings.

Yb2Co3Al9 and Yb2Co3Ga9 are isostructural compounds with an orthorhombic crystal structure having a unique Yb site. The Yb ions are in a trivalent state in Yb2Co3Al9 and order magnetically near 1.2 K inferred both from low-temperature heat capacity and Yb-170 Mossbauer spectroscopy measurements. A well-resolved hyperfine field split spectrum at 0.06 K yields a spontaneous moment of 0.93 mu (B)/Yb. From the thermal variation of the 4f specific heat and of the 4f quadrupolar moment in the paramagnetic phase. we could determine the energies of the four crystal-field states of Yb3+ and we find that the overall splitting is about 180 K. By contrast, the 4f electronic state of Yb ions in Yb2Co3Ga9 is strongly hybridized with the conduction-electron band states. with valency close to 2.9 as determined by L-111-edge x-ray-absorption measurements. The Pauli paramagnetic ground state. with chi similar or equal to 12.5x10(-3) emu (Yb mol)(-1) and the thermal variation of the susceptibility on the one hand, the Sommerfeld coefficient gamma similar or equal to 120 mJ (Yb mol)(-1) K-2 and the thermal variation of the 4f heat capacity on the other hand, are quantitatively well explained in the Coqblin-Schrieffer limit of the J = 7/2 Kondo impurity, with a characteristic hybridization (or Kondo) scale T-0=235 K. From the Yb-170 Mossbauer spectra recorded up to 77 K and Yb-172 perturbed angular correlation data recorded up to 1000 K, we find that the thermal variation of the 4f quadrupolar moment Q(4f)(T) in Yb2Co3Ga9 scales with the magnetic susceptibility chi (T), as predicted by theory to occur in the case the Kondo scale is larger than the crystal-field splittings.