Direct evidence of spin filtering across MnFe$_2$O$_4$ tunnel barrier by Meservey-Tedrow experiment

Abstract : A spin filtering effect has been evidenced in epitaxial MnFe$_2$O$_4$ tunnel barriers directly by Meservey-Tedrow experiments. The asymmetry of the Zeeman-split tunneling conductance curves of the superconducting Al spin analyzer in Pt(111)/MnFe$_2$O$_4$(111)/$\gamma$-Al$_2$O$_3$(111)/Al tunnel junctions revealed a positive spin-polarization (up to + 9%), proving the potential of manganese ferrite for generation of a spin-polarized current. A negatively polarized spin filtering being expected theoretically, different mechanisms are discussed to explain both sign and amplitude of the measured spin-polarization.