Superconductivity and ferromagnetism are two competing phenomena: a superconductor expels a magnetic field, which in turn tries to weaken the superconductivity. However, the coexistence of conventional spin singlet (two electrons of opposite spin) superconductivity, and ferromagnetism (electron spins are aligned parallel) may be achieved by fabricating superconductor/ferromagnet (S/F) hybrid structures. The interplay between conventional superconductivity and magnetism in S/F systems leads to a fast decay of the order parameter in the F-layer as the two electrons from the spin-singlet Cooper pair enter different spin bands and rapidly lose phase coherence. It has been predicted that spin triplet pair correlations can be created near the S/F interface in the presence of certain kinds of magnetic inhomogeneity. If the spin triplet correlations are present at the SF interface, then the spin triplet proximity effect persists over much longer distances in the ferromagnet. These correlations exhibit a new type of symmetry: they are odd in frequency or time. The essence of this project was a systematic approach to observe these correlations in Co-based Josephson junctions. Since our early data didn't show any sign of long-range spin triplet correlations, we decided to split the observation process into two stages: generation and propagation. Generation of spin triplet correlations at the SF interface is provided by a thin layer of Cu0.48 Ni0.52 alloy placed next to the Nb electrodes. For the propagation, we used a Synthetic Antiferromagnet, SAF configuration consisting of Co(x)/Ru(0 6 nm)/Co(x) as thick as 2x = 39 nm. We observed a large enhancement in the supercurrent compared to junctions without the CuNi alloy. These experimental observations provide strong evidence for the long triplet nature of these correlations.
|Adviser||Norman O. Birge|
|School||MICHIGAN STATE UNIVERSITY|
|Subjects||Electromagnetics; Condensed matter physics|
About ProQuest Dissertations & Theses
With nearly 4 million records, the ProQuest Dissertations & Theses (PQDT) Global database is the most comprehensive collection of dissertations and theses in the world. It is the database of record for graduate research.
PQDT Global combines content from a range of the world's premier universities - from the Ivy League to the Russell Group. Of the nearly 4 million graduate works included in the database, ProQuest offers more than 2.5 million in full text formats. Of those, over 1.7 million are available in PDF format. More than 90,000 dissertations and theses are added to the database each year.