Tunnel effect in ferromagnetic half-metal Co${}_2$CrAl-superconductor heterostructures

Abstract

Ferromagnetic half-metal Co${}_2$CrAl films and tunnel contacts Co${}_2$CrAl - insulator (I) - Pb are fabricated and investigated. It is found that the normalized differential conductivity ${\sigma }^{\mathrm{FS}}$ of such tunnel junctions with low resistance is larger than the normalized differential conductivity ${\sigma }^{\mathrm{NS}}$ of known normal metal - I - superconductor type tunnel junctions. It is shown that the observed increase in ${\sigma }^{\mathrm{FS}}$ is caused by the accumulation of spin polarized electrons in a superconductor and can be used for estimating the spin polarization degree $P$ in ferromagnets. This method shows that $P$ of L2${}_1$-type ordered Co${}_2$CrAl Heusler alloy films at $T=4.2\mathrm{K}$ is close to 1.

5 pages, 4 figures