Experimental Study of Superconductor/Ferromagnet Proximity Effects

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

Non-technical Abstract: Many useful electronic devices are made from ferromagnetic films, such as read and write heads for computer hard drives. Useful devices are made from superconducting films, too, including medical systems that detect magnetic fields from heartbeats and brain activity. Recent advances in the sophistication of experimental apparatus for making thin-film structures and for measuring them, and advances in theory, have opened a new avenue for possible devices that incorporate superconducting and ferromagnetic films in close proximity. The really exciting aspect of the science, and an important mechanism for new device functionalities, comes from the persistence of superconductivity inside the ferromagnet when the two materials are in such intimate contact such that electrons can diffuse freely from superconductor to ferromagnet and back. This project will study superconducting electrons in the ferromagnet directly via magnetic field screening measurements in large and nano-scale devices, and indirectly via electron tunneling measurements. The project will involve graduate and undergraduate students in fabrication of SC/FM devices as well as sophisticated measurements. Technical Abstract: Superconductivity and ferromagnetism are antithetical, the former demanding that electrons form spin-zero pairs and the latter pressing for parallel electron spins. Recently it has been appreciated that sample fabrication and measurement techniques have become sufficiently sophisticated that the mutual interactions of superconductors in intimate contact with ferromagnets can be reproducibly created and studied. A surprising result of theory is that superconductivity can persist into the ferromagnet. This project will explore the effective superfluid density associated with supercurrents in the FM layer of various SC/FM bilayer and trilayer structures. The superfluid density will be measured directly via magnetic screening measurements involving the mutual inductance of coils on opposite sides of a SC/FM bilayer or trilayer, and via transport measurements on nanoscale patterned wires, to see the effects of reduced dimensionality. It will also be studied via tunneling measurements into the FM film of a SC/FM bilayer that is carrying a supercurrent. The project will involve graduate and undergraduate students in fabrication of SC/FM devices as well as sophisticated measurements.