Spin polarization of electrons tunneling from3dferromagnetic metals and alloys

Abstract

The electron spin polarization (ESP) of a wide range of alloys of Cr, Cu, Fe, Mn, or Ti in Ni was measured by the spin-polarized tunneling technique using thin-film Al-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$-ferromagnetic-alloy tunnel junctions. The measurements were made at a temperature of 0.4 K and in an applied magnetic field of 3.5-4.0 T. A phenomenological correlation between electron spin polarization and atomic magnetic moment which was previously observed for the pure ferromagnetic elements (Fe, Co, Ni), is shown to be valid for all the alloys measured. Various methods were used for the deposition of the thin-film alloys. Each of these methods gave the same relative values of ESP when compared to Ni deposited by the same method. The dependence of the measured polarization on deposition parameters of the ferromagnetic films is presented. The effect of the properties of the superconducting aluminum films and other sources of systematic error are analyzed. The present results greatly constrain possible explanations of spin-polarized tunneling currents from $3d$ ferromagnetic metals based on current theories of itinerant ferromagnetism.