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Reanalysis of crystal-field parameters for Nd3+ ions in Nd2BaCuO5 and Nd2BaZnO5 based on standardization, multiple correlated fitting technique, and dataset closeness.
Autorzy
Rok wydania
2007
Czasopismo
Numer woluminu
76
Strony
1-11
DOI
10.1103/PhysRevB.76.125116
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
This paper elucidates some subtle properties of the orthorhombic and monoclinic symmetry crystal-field (CF) Hamiltonians (HCF), which are not fully understood by some authors. These properties bear on interpretation of experimental data obtained in, e.g., optical spectroscopy, inelastic neutron scattering, and magnetic susceptibility measurements. Our reanalysis of CF parameters (CFPs) is based on application of the standardization idea as well as the idea of dataset closeness. The closeness of any two CFP sets may be represented by the closeness factor C and the norm ratio R=NA∕NB for the respective HCF terms: k=2,4,6, and the global ones Cgl. The specific aims of this paper are twofold. The first aim is to clarify the controversy arising when comparing the standard CF parameters with the nonstandard CFPs. This controversy, originating from the lack of awareness of the standardization applicable to the orthorhombic (as well as monoclinic and triclinic) CFP datasets, is evident, e.g., in the recent study of Nd3+ ion in Nd2BaCuO5 by R. S. Puche et al. [Phys. Rev. B 71, 024403 (2005)]. This leads to an unjustified criticism of the data of other authors. Consideration of standardization and dataset closeness also helps in identifying other inconsistencies concerning R. S. Puche et al.’s results. The second aim is to determine the alternative physically equivalent CFP datasets generated by the standardization transformation. These CFP datasets are utilized in the multiple correlated fitting technique (MCFT) to improve the reliability of the final fitted CFPs. Additonal refittings of the original energy level data are carried out starting from distinct regions in the parameter space. The independently fitted nonstandard CFPs obtained in this way are then transformed to the standard region and intercorrelated. Our considerations enable us to solve the controversy in question and improve the understanding of the intricacies inherent in the low-symmetry CFP datasets. A comparative analysis of the CFPs for various rare earth R3+ ions in R2BaXO5 (X=Cu, Zn, Ni, and Co), and related crystals will be carried out elsewhere.
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