Long range supercurrents in ferromagnetic CrO₂ using a multilayer contact structure

Abstract

We report measurements of long ranged supercurrents through ferromagnetic and fully spinpolarized CrO2 deposited on TiO2 substrates. In earlier work, we found supercurrents in films grown on sapphire but not on TiO2. Here we employed a special contact arrangement, consisting of a Ni/Cu sandwich between the film and the superconducting amorphous Mo70Ge30 electrodes. The distance between the contacts was almost a micrometer, and we find the critical current density to be significantly higher than found in the films deposited on sapphire. We argue this is due to spin mixing in the Ni/Cu/CrO2 layer structure, which is helpful in the generation of the odd-frequency spin triplet correlations needed to carry the supercurrent.

Giant triplet proximity effect in superconducting pseudo spin valves with engineered anisotropy

“…For example, consider a S-F -F-F -S Josephson junction [7]: If the F and F layer magnetizations are collinearly aligned, spin-zero triplet pairs form which, like singlet pairs, are short ranged [8] with a coherence length in F metals of only a few nanometers (Ni [9][10][11][12], NiFe [13,14], Co [11,15,16], and Fe [17,18]). However, if F and F layer magnetizations are noncollinearly aligned spin-one triplet pairs form and the coherence length is greatly extended [19][20][21][22][23][24][25][26][27]. See also spectroscopic works on triplet S-F structures in Refs.…”

Evidence for spin selectivity of triplet pairs in superconducting spin valves

“…More direct evidence for the generation of triplet pairing was obtained from S-F-S Josephson junctions in which, if interfacial spin-mixer layers were present, supercurrents could be measured through F-layer thicknesses much larger than the singlet coherence length [15][16][17][18][19][20][21][22][23] . As spin-one triplet pairs, unlike singlet pairs, can carry spin, these results mean that combining superconducting and spin electronics (superconducting spintronics) opens up real potential for practical lowtemperature applications 24 .…”

Anomalous transport in half-metallic ferromagnetic CrO2

“…Also, its half-metallic character was recently used for the realization of long-ranged supercurrents. [8][9][10] However, the electronic properties of CrO 2 are still not fully understood. For instance, the resistivity between 10 and 300 K is usually described in terms of an excitation gap, 11,12 but a clear connection with an electronic or spin gap excitation cannot be made.…”