High pressures and ferromagnetic order in EuB6

We have measured the electrical resistivity rho(T) of single crystals of EuB6 for temperatures from 1.2 to 300 K, and pressures from 1 bar to 169 kbar. The room temperature resistivity rho(300 K). is dramatically reduced with pressure, while the double ferromagnetic ordering temperatures T-c(+,-) are strongly enhanced. We argue that magnetic order is driven by the Ruderman-Kittel-Kasuya-Yosida interaction between Eu moments and pockets of carriers at the semimetallic X point. With pressure, the band overlap increases, leading to an increase in carriers at the Fermi surface and the decrease of the spin disorder scattering in the paramagnetic state.