Alternative crystal field parameters for rare-earth ions obtained from various techniques: IV. Comparative analysis of crystal field parameters obtained from inelastic neutron scattering and related studies of RE ions (RE = Er~(3+), Ho~(3+), Nd~(3+), Pr~(3+)) in REBa_2Cu_3O_(7-δ) high-T_c superconductors

摘要

This is fourth paper in a series devoted to reanalysis of the non-standard and standard crystal-field (CF) parameter (CFP) sets obtained from various experimental techniques and theoretical models for trivalent rare-earth (RE) ions in high-critical-temperature (high-T_c) superconductors and related systems. In this paper the experimental orthorhombic CFPs, obtained mostly by inelastic neutron scattering techniques and to a lesser extent by magnetic susceptibility and specific heat measurements as well as the respective theoretical CFPs for Er~(3+), Ho~(3+), Nd~(3+), and Pr~(3+) ions in REBa_2Cu_3O_(4-δ) compounds, are considered. Several problems identified due to the comparative CFP analysis: (i) confusing notations used for operators and CFPs, (ii) different scaling factors and units used for CFPs, and (iii) lack of clear definitions of the axis systems used to express CFPs, were clarified. For each ion studied the available experimental and theoretical CFP sets are analyzed, standardized, and presented in a unified way. The large number of CFP sets prevents calculation of the five additional alternative sets for each originally reported CFP set. Instead, the alternative CFP sets are determined using the package CST for an average set calculated for selected compatible sets for each ion. These alternative CFP sets may be utilized in the multiple correlated fitting technique to improve reliability of the final fitted CFPs. The present results may facilitate future spectroscopic determination of CFPs as well as increase reliability of fitted and theoretical CFPs for RE~(3+) ions in high-T_c superconductors REBa_2Cu_3O_(4-δ) and related systems.