Inelastic neutron scattering experiments of the crystal-field (CEF) splitting of the R 3+ ions (R = Ho, Er, Tm) in the superconductor RNi 11 2 B 2 C have been performed in the paramagnetic as well as in the magnetically ordered state in order to deduce the CEF parameters which in turn determine the thermodynamic magnetic properties of these systems. The calculated ordered magnetic moments are in agreement with magnetic neutron diffraction results, i.e. both the easy axis and the size of the zero-field moments are correctly reproduced. In addition, the entropy involved in the magnetic ordering obtained from specific heat measurements is in correspondence with the number of low-lying CEF states observed in this study. Our CEF parameter set also reproduces both the behavior and the anisotropy in M/H measured for single crystals.
PACS. 74.72Bk -Y-based compounds. PACS. 78.00 -Optical properties of condensed-matter spectroscopy and other interactions of PACS. 79.20Kz -Other electron-impact emission phenomena. matter with particles and radiation.
The NQR and NMR spectra of copper in polycrystalline samples of YBazCu30 ~ and GdBa2Cu30 ~ with different oxygen concentration x have been measured at 4.2 and 1.2 K. The different influence of Gd spins on the Cu(1) and Cu(2) sites was used to separate the contributions of both sites in the spectra. The quantitative analysis of the spectra in the region 6.3 < x < 6.75 allows the following conclusions about the ordering of the oxygen ions in the chains of the Cu(t) planes and about the magnetic state of the Cu(2) ions to be drawn, At about x = 6.5 oxygen orders in the ortho-II structure with every second chain filled. For higher x the coexistence of ortho-II and oxygen depleted ortho-I (all chains filled to about 80 %) gives the best description of the results. The average length of the Cu--O chains, n, is about 10 oxygen atoms per chain in the region of the 60 K plateau and decreases rapidly at lower x. The superconductivity disappears when n < 6. No signal of the Cu(2) sites is found in samples with T~ below the 60 K plateau due to the slowing down of the fluctuation tate of the electron spins of the Cu(2) ions. Magnetic order appears only in samples which do not become superconducting.
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