Tunneling measurements of conduction-electron-spin polarization in heavy rare-earth metals

The spin polarization $P$ of electrons tunneling from the ferromagnetic heavy rare-earth metals Gd, Tb, Dy, Ho, Er, and Tm was measured and in each case found to be positive (in the direction of the majority spin). For Yb and Lu, which are not ferromagnetic, $P$ was found to be zero. The values of $P$ are approximately proportional to the saturation magnetic moments of the conduction electrons for the different elements. Analysis of the data and possible sources of error in these measurements are discussed. Conductance measurements of Al-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$-Gd junctions at voltages up to 0.5 V are also presented.