ESR study of theEu2+g-value in the metallic phase of cubic hexaborideCa1−xEuxB6(0.15≲x⩽1.00)

Abstract

The angular, magnetic field, and temperature dependence of the ${\mathrm{Eu}}^{2+}(4{f}^{7},S=7∕2)$ $g$-value in ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}{\mathrm{B}}_{6}(0.15\ensuremath{\lesssim}x\ensuremath{\leqslant}1.00)$ is measured by means of electron spin resonance at two microwave frequencies, 9.4 and $34.4\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. The $g$-value is found to be anisotropic and magnetic-field-dependent. The reduction with field of the positive $g$-shift is interpreted in terms of the exchange interaction between the localized ${\mathrm{Eu}}^{2+}4{f}^{7}$ electrons with the conduction ${\mathrm{Eu}}^{2+}$ $5d$-like electrons and B $2p$-like holes. The angular, temperature, and $x$ dependence of the anisotropy of the $g$-value can be attributed to demagnetization effects due to the platelet-like shape of the samples. High-resolution synchrotron x-ray diffraction experiments show the absence of distortions larger than $\ensuremath{\delta}a∕a\ensuremath{\sim}{10}^{\ensuremath{-}4}$. However, a mechanism for the anisotropy based on a weak tetragonal lattice distortion arising from the crystal surface cannot be excluded.