A. Velichkov

Nuclear 111Cd probes detect a hidden symmetry change at the γ → α transition in cerium considered isostructural for 60 years

We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium: α″ (C2/m space symmetry) and α′ (α-U structure).

Hyperfine field assessment of the magnetic structure of ZrZn2

Time differential perturbed angular gamma-gamma-correlation (TDPAC) method on 111Cd nuclei probes inserted in ZrZn1.9 is used to measure the magnetic hyperfine fields (MHF) at Zr and Zn sites and the electric field gradient (EFG) Vzz at Zn sites as a function of temperature at various pressures and as a function of pressure at the temperature 4 K. Our data indicate that the local magnetic moment of Zr in the magnetically ordered state is substantially larger than its value obtained from the macroscopic measurements and that there is also an induced magnetic moment at the Zn site. We conclude that ZrZn2 is not a simple ferromagnet and discuss a possible type of its magnetic ordering.

Investigation of hyperfine quadrupole interactions in UGe2 and UAl2 compounds on 111Cd probe nuclei by the perturbed angular correlation method

The parameters of nuclear quadrupole hyperfine interaction in intermetallic UGe2 and UAl2 compounds have been measured in a temperature range of 100–300 K using the perturbed angular γγ correlation method on 111Cd probe nuclei. The results obtained for UGe2 indicate a pronounced anisotropic character in the distribution of f electrons in agreement with the calculation of the electronic structure of this compound. The hybridization degree between f electrons of U and p electrons of Al in UAl2 is lower than the hybridization degree between f electrons of U and p electrons of Ge in UGe2.

Two-stage pressure-induced Yb valence change in the hexagonal Laves phase YbAg2 : Investigation by time differential perturbed angular γ−γ correlation spectroscopy method and density functional calculations

We have studied the C14 hexagonal Laves phase of YbAg

Study of the electric field gradient at 111Cd in the RAl3 compounds synthesized under high pressure

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Lowering of the spatial symmetry at the gamma ->alpha phase transition in cerium

at normal conditions and under external pressure up to 19 GPa by the time-differential perturbed angular

PAC spectrometer for condensed matter investigation

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Electric field gradients in MgB2 synthesized at high pressure: 111Cd TDPAC study and ab initio calculation

correlation spectroscopy (TDPAC) using

111-Cd time-differential perturbed angular correlation study of pressure-induced valence changes in YbAl2

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Lowering of the spatial symmetry at the γ → α phase transition in cerium

Cd probe nuclei. Under pressure the valence of Yb undergoes a two stage transition from 2.8 to 3. The two stage scenario is characterized by two distinct quadrupole frequencies of