Compensated CoGd Ferrimagnets in Magnetic Josephson Junctions*

The rare earth-transition metal ferrimagnet Co_1-xGd_x has been studied for application in superconducting electronics. At a carefully chosen Gd concentration, the Co and Gd moments perfectly cancel leading to a zero-moment compensation point. Point-contact Andreev reflection measurements [1] have shown that at the compensation point there is still a net spin polarization of the transport current. This raises the possibility of application in electronics requiring a magnetic material with little stray field, such as cryogenic magnetic memory. As the compensation point can vary significantly as a function of temperature and thickness, we present SQUID VSM data on thin films taken at cryogenic temperatures. We also present the results of transport measurements on superconductor-ferrimagnet-superconductor Josephson junctions over a range of thicknesses for CoGd alloys near their compensation point.
[1] Naylor et al., Phys. Rev. B 85, 064410 (2012)