Magnetic and Structural Properties of Europium Metal and Europium Monoxide at High Pressure

The change of the Néel temperature of europium metal and of the Curie temperature of EuO with pressure has been measured up to 90 kbar by resistivity and initial-permeability methods, respectively. The compressibility of Eu and EuO has been determined relative to NaCl in the same range of pressure by powder x-ray diffraction methods. The compressibility is represented by the Birch equation; for Eu $B_0=124\mathrm{}$ kbar and $\xi =0.9\mathrm{} (\frac{d{\beta }_0}{\mathrm{dp}}=2.8)$ and the standard deviation is 1.8; for EuO, $B_0=1070\mathrm{}$ kbar and $\xi$ was assumed to be zero and the standard deviation is 2.8. For Eu, $d\ln \frac{T_N}{d}\ln V\approx 0$ down to $\frac{V}{V_0}=0.8\mathrm{}$. The initial slope for EuO is $d\ln \frac{T_c}{d}\ln V=-6\mathrm{}\pm 2$. The results are discussed in terms of the theories of exchange interaction in the heavy rare-earth metals and the europium chalcogenides.