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We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0–28.2 GPa) and single crystal x-ray diffraction (SXD) (0–20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K0 = 62(1) GPa and its pressure derivative, K0 = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

The temperature dependence of the structural parameters and the occurrence of magnetism in UPdSn and UCuSn are measured by using neutron diffraction. Rietveld refinement of neutron diffraction data is used for determining the shortest interatomic distances for temperatures between 15 K and room temperature and the changes in the interatomic distances have caused changes in the hybridization effects, leading to the formation of a magnetic ground state for both compounds.

57Fe-enriched Fe4O5 samples were synthesized in a laser-heated diamond anvil cell at a pressure of about 15 GPa and a temperature of about 2000 K. Nuclear forward scattering (NFS) spectra were collected in the range 0-40 GPa and were combined with first-principles calculations to provide insights into the magnetic properties of Fe4O5. NFS spectra show that strong magnetic interactions persist up to 40 GPa and that they are generated by a single magnetic contribution. The hyperfine magnetic field (Bhf) and quadrupole splitting (QS) are in the ranges 51-53 T and 0.40-1.2 mms-1, respectively. The QS shows an intriguing evolution with pressure, with a fast increase from 0.4 to 10.mms-1 between 0 and 10 GPa and a slow increase up to 1.2 mms-1 in the range 10-40 GPa. First-principles calculations suggest an antiferromagnetic ordering for the three sites, and similar magnetic moments in the range ~3.6-3.8 μB/Fe. These values, typical of strongly correlated Fe magnetic systems, are in agreement with the experimental estimated average moment of ~3.8 μB/Fe. The single contribution to the NFS spectrum and the similar calculated magnetic moments suggest that the iron atoms at the three crystallographic sites have similar electronic arrangements. [ABSTRACT FROM AUTHOR]

The structural properties of LaRu2 P2 under external pressure have been studied up to 14 GPa, employing high-energy x-ray diffraction in a diamond-anvil pressure cell. At ambient conditions, LaRu2 P2 (I4/mmm) has a tetragonal structure with a bulk modulus of B = 105(2) GPa and exhibits superconductivity at Tc = 4.1 K. With the application of pressure, LaRu2 P2 undergoes a phase transition to a collapsed tetragonal (cT) state with a bulk modulus of B = 175(5) GPa. At the transition, the c-lattice parameter exhibits a sharp decrease with a concurrent increase of the a -lattice parameter. The cT phase transition in LaRu2 P2 is consistent with a second-order transition, and was found to be temperature dependent, increasing from P = 3.9(3) GPa at 160 K to P = 4.6(3) GPa at 300 K. In total, our data are consistent with the cT transition being near, but slightly above 2 GPa at 5 K where superconductivity is suppressed. Finally, we compare the effect of physical and chemical pressure in the R Ru2 P2(R = Y, La-Er, Yb) isostructural series of compounds and find them to be analogous. [ABSTRACT FROM AUTHOR]

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0(5) GPa for temperatures below 150 K. Density functional theory calculations also find a sudden transition to a collapsed tetragonal state near 4 GPa, as As-As bonding develops across the Ca layer. Bonding across the K layer only occurs for p≥12 GPa. These findings demonstrate a different type of collapsed tetragonal phase in CaKFe4As4 as compared to CaFe2As2: a half-collapsed tetragonal phase. [ABSTRACT FROM AUTHOR]