Conduction-Band Tunneling and Electron-Spin Polarization in Field Emission from Magnetically Ordered Europium Sulfide on Tungsten

We measured the temperature dependence of the current and spin polarization, and determined the work functions from Fowler-Nordheim plots. The current increases exponentially with decreasing temperature. Work-function data can be related directly to the height of the internal W-EuS barrier. This barrier is lowered by magnetic splitting of the EuS conduction band for one electron-spin state which should lead to a spin polarization of unity. The measured spin polarization, however, is equal to the polarization of the $4f^7$ electrons of europium.