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The magnetic properties of newly prepared Tm 2 Ir 2 O 7 were investigated by means of magnetization and specific heat measurements and compared to the properties of other heavy rare-earth pyrochlore iridates. A bifurcation of zero-field-cooled and fieldcooled magnetization coinciding with the onset of the specific heat anomaly indicated the magnetic ordering of the Ir sublattice, in agreement with studies on other pyrochlore iridates. The phase diagram depicting the ordering/metal-insulator-transition temperature dependent on the rare-earth ionic radius was updated and completed. Magnetic dc susceptibilities and magnetic contributions to the specific heat of Er, Tm, and Yb analogues were well described by crystal field parameters and eigenenergies, previously reported for Er 2 Ir 2 O 7 and Yb 2 Ir 2 O 7 . The crystal field parameters for, the so-far-unstudied, Tm 2 Ir 2 O 7 were calculated by scaling the Er 2 Ir 2 O 7 parameters employing appropriate Stevens factors for Er 3+ and Tm 3+ . Iridates with the Kramers' Er 3+ and Yb 3+ ions revealed a splitting of the ground-state doublet, leading to a broad anomaly in specific heat at around 2 K and 3 K, respectively. The previously reported low value of magnetic moment in Yb 2 Ir 2 O 7 was confirmed by magnetization measurements. The nonmagnetic ground-state crystal-field singlet in Tm 2 Ir 2 O 7 dictated by Tm trigonal Wyckoff position was confirmed by both evolution of specific heat at low temperature and temperature dependence of the magnetic entropy.

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No abstract

CeCuAl crystallizing in the tetragonal BaNiSn-type structure and CeCuAl solid solutions were investigated by means of elastic and inelastic neutron scattering. Powder neutron diffraction brought information on both temperature evolution of crystallographic parameters and magnetic order at low temperatures. No structural change was observed in the investigated temperature range from 1.5 to 300 K. Weak magnetic peaks outside nuclear Bragg positions observed in solid solutions with 0.90 ≤ x ≤ 1.10 were described by the propagation vector k = (0.40 + δ, 0.60 + δ, 0), where δ ≈ 0.02 and δ ≈ 0.01. The magnetic structure of CeCuAl consists of two components: an anti-ferromagnetic one described by the same k and a ferromagnetic one with k = (0, 0, 0) and magnetic moments lying within the tetragonal basal plane. The evolution of magnetic excitations as a function of Cu-Al concentration in CeCuAl was studied by inelastic neutron scattering. The measured spectra of CeCuAl and the solution with x = 0.95 point to a three-magnetic-peak energy scheme, while only two excitations are expected from the local symmetry conditions on Ce atoms. The standard two-peak spectrum of crystal electric field excitations was observed for Cu-Al substitutions further from the 1:1:3 stoichiometry (x = 0.75 and 1.10). The intermediate concentrations (x = 0.90 and 1.05) exhibit spectra on the border between the former cases with a less clear pronounced first inelastic magnetic peak. The observed behavior is discussed considering the evolution of structural parameters in the CeCuAl system and the coupling between the lattice vibrations and the crystal electric field excitations.