A study on the magnetic susceptibilities and optical absorption spectra on single crystals of Gd(III) pyrogermanate

Abstract

The paper reports for the first time the experimental results of the measurements of magnetic susceptibilities ( K ⊥ and K |) and their anisotropy (Δ K) between 300 and 21.8 K and the optical absorption spectra (UV region) at 12.5 K on single crystals of gadolinium pyrogermanate (GdPG). The anisotropy, which is only 211×10 -6 emu/mol at room temperature and increases by two orders of magnitude at 21 K, is predominantly a crystal field (CF) effect on the 8S 7 2 ground term, through higher order perturbations. Interpretation of the observed magnetic data was carried out by considering a conventional spin Hamiltonian ( H s) to derive expressions for K ⊥ and K | in terms of four effective crystal field parameters (ECFP). The value s of ECFP were varied to obtain a very close fitting between the theoretical and experimental values of K ⊥, K |, δ K and K̄ The splitting of the 8S 7 2 term corresponding to these values of ECFP was found to be large, which suggests a strong CF effect in GdPG, as also observed in other RPG crystal studied earlier. The thermal characteristics of the magnetic anisotropy below 30 K deviate by about 5% which could not be explained by CF effects alone. A series expansion method was adopted to analyse the results of K ⊥ and K | below 30 K, however the corresponding coefficient B 2α and B 3α were observed t o be unusually high indicating the presence of CF effect even in this temperature region. The Schottky specific heat, C sch, between 300 and 21 K for GdPG has been calculated and this shows a maximum at T max=17 K.