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Different Gd3+ sites in CaB6: an ESR study

R. R. Urbano·C. Rettori·G. E. Barberis·M. Torelli·A. Bianchi·Z. Fisk·P. G. Pagliuso·A. Malinowski·M. F. Hundley·J. L. Sarrao·S. B. Oseroff
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Abstract

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.

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R. R. Urbano, C. Rettori, G. E. Barberis, M. Torelli, A. Bianchi, Z. Fisk, P. G. Pagliuso, A. Malinowski, M. F. Hundley, J. L. Sarrao, S. B. Oseroff. 2001-07-17. Different Gd3+ sites in CaB6: an ESR study. https://arxiv.org/abs/cond-mat/0106550

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