The local environment of Gd3+ (4f7 S=7/2) ions in single crystals of Ca1-xGdxB6 (0.0001 < x < 0.01) is studied by means of Electron Spin Resonance (ESR). The spectra for low concentration samples (x < 0.001) show a split spectrum due to cubic crystal field effects(CFE). The lineshape of each fine structure line is lorentzian, indicating an insulating environment for the Gd3+ ions. For higher concentrations (0.003 < x < 0.01), the spectra show a single resonance (g=1.992(4), DH1/2 ~ 30-60 Oe) with no CFE and dysonian lineshape indicating metallic environment for the Gd3+ ions. For intermediate concentrations, a coexistence of spectra corresponding to insulating and metallic regions is observed. Most of the measured samples show the weak ferromagnetism (WF) as reported for Ca1-xLaxB6 (x ~ 0.005), but, surprisingly, this WF has no effect in our ESR spectra either for metallic or insulating environments. This result suggests that the ferromagnetism in these systems might be isolated in clusters (defect-rich regions) and its relationship with metallicity is nontrivial.
@article{arxiv.cond-mat/0106550,
title = {Different Gd3+ sites in CaB6: an ESR study},
author = {R. R. Urbano and C. Rettori and G. E. Barberis and M. Torelli and A. Bianchi and Z. Fisk and P. G. Pagliuso and A. Malinowski and M. F. Hundley and J. L. Sarrao and S. B. Oseroff},
journal= {arXiv preprint arXiv:cond-mat/0106550},
year = {2019}
}