Proximity effect in [Nb(1.5 nm)/Fe( x )] 10 /Nb(50 nm) superconductor/ferromagnet heterostructures

• Published in: Beilstein journal of nanotechnology 2020-08, Vol.11 (1), p.1254-1263
• Main Authors: Khaydukov, Yury, Pütter, Sabine, Guasco, Laura, Morari, Roman, Kim, Gideok, Keller, Thomas, Sidorenko, Anatolie, Keimer, Bernhard
• Format: Article
• Language: English
• Subjects: ferromagnet; Full Research Paper; iron (fe); mixed state; Nanoscience; Nanotechnology; neutron reflectometry; niobium (nb); proximity effects; superconductor
• ISSN: 2190-4286; 2190-4286
• DOI: 10.3762/bjnano.11.109

We have investigated the structural, magnetic and superconduction properties of [Nb(1.5 nm)/Fe( x )] 10 superlattices deposited on a thick Nb(50 nm) layer. Our investigation showed that the Nb(50 nm) layer grows epitaxially at 800 °C on the Al 2 O 3 (1−102) substrate. Samples grown at this condition possess a high residual resistivity ratio of 15–20. By using neutron reflectometry we show that Fe/Nb superlattices with x < 4 nm form a depth-modulated FeNb alloy with concentration of iron varying between 60% and 90%. This alloy has weak ferromagnetic properties. The proximity of this weak ferromagnetic layer to a thick superconductor leads to an intermediate phase that is characterized by a suppressed but still finite resistance of structure in a temperature interval of about 1 K below the superconducting transition of thick Nb. By increasing the thickness of the Fe layer to x = 4 nm the intermediate phase disappears. We attribute the intermediate state to proximity induced non-homogeneous superconductivity in the structure.