VARIATION OF THE ELECTRON-SPIN POLARIZATION IN EUSE TUNNEL-JUNCTIONS FROM ZERO TO NEAR 100-PERCENT IN A MAGNETIC-FIELD

A thin film of EuSe was used as a tunnel barrier between the normal metal Ag and superconducting Al. Tunneling characteristics at 0.45 K showed the following: (1) the absence of exchange splitting of the EuSe conduction band in zero magnetic field, where EuSe is antiferromagnetic; (2) field-dependent spin polarization of the tunneling electrons as high as 97% at H greater-than-or-equal-to 1.2 T, (3) enhanced Zeeman splitting of the Al quasiparticle states because of the exchange interaction at the Al-EuSe interface, (4) a decrease in tunnel resistance by as much as 75% in a magnetic field greater-than-or-equal-to 1.7 T. The results show that EuSe barrier junctions provide field-tunable resistors and sources of low-energy polarized electrons.