Spin Polarization in the High-$H_{c_2}$ Compound ${\mathrm{Sn}}_{0.5}$${\mathrm{Eu}}_{0.5}$${\mathrm{Mo}}_6$${\mathrm{S}}_8$

NMR studies of ${}_{}{}^{95}{}_{}{}^{}\mathrm{Mo}$ show that the enhancement of $H_{c_2}$ (∼ 100 kG) in Eu-substituted Sn${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ arises from a negative $s$-band spin polarization at the Mo site. Mössbauer-effect studies of ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ indicate a small positive polarization at the Eu site and a weak Korringa relaxation, which is consistent with the weak depression of $T_c$. The ${\mathrm{Eu}}^{2+}$ isomer shift (-14.0 mm/sec) shows an extremely low $s$-electron density at the rare-earth site.