Superconducting Surface Spin Valve Effect at the Ferromagnet/Superconductor Interface Carmen C. Almasan, Kent State University, DMR 0705959 Recently a surface spin valve effect was observed within a few atomic layers at the ferromagnet/normal (F/N) interface. This is due to the fact that the ferromagnetic spins at such an interface are significantly different from the magnetic character of the spins inside the F layer and they can act as current- or field-driven spin valves with respect to the magnetization in the interior of the ferromagnetic layer. Based on these results we had anticipated that a superconductive S surface spin valve effect could be present in the ferromagnet/superconductor La0.7Ca0.3MnO3/ YBa2Cu3O7-d (LCMO/YBCO) bilayer since it has been shown that the magnetic coupling near the LCMO/YBCO interface is very weak compared with the one for the bulk LCMO. So, the direction of interface magnetization can be tuned by the rotation of a small magnetic field H, while not affecting the direction of the bulk magnetization M. In this way, the parallel/antiparallel alignment of the surface and bulk magnetizations are created. This finding would facilitate the development of superconductive magnetoresistive memory device. Our results show the presence of a surface spin valve effect in this system (see figure below), only in the superconducting state of the bilayer. We propose that this is based on the S/F proximity effect; i.e., the relative orientation between the surface and bulk Ms of LCMO modulates the exchange interaction, hence, the spatial dependence of the Cooper pair wave function, hence the magnetoresistance of the bilayer. Angular dependent magnetoresistance data measured at 45 K and for a magnetic field H of 35 Oe, with the current applied along the  crystallographic direction. Inset: Sketch of bulk magnetization M (pinned along easy axis) and of rotating H.
Superconducting Surface Spin Valve Effect at the Ferromagnet/Superconductor Interface Carmen C. Almasan, Kent State University, DMR 0705959 Education An essential activity performed has been the education of three graduate students and one postdoc. They did not only pursue cutting edge science, but they also became knowledgeable in a highly varied array of skills, technologies, and forefront topics in condensed matter physics by being involved in all phases of their project. These phases may include equipment and electronics design and construction, experiment “debugging”, data acquisition and analysis, and comprehension of and comparison with the relevant theoretical results. All three students got their Ph.D. during this year. Two of them are presently postdocs at University of Crete, Greece, while the third one continued as a postdoc in my lab. Outreach As part of the outreach activities of the PI, AP and Honors Physics students from nearby high schools visited her laboratory and learned about physics in general and superconductivity and magnetism in particular, through demonstrations and short lectures given by the PI and her graduate students. In this way, the high school students were exposed to a research environment and were given a flavor of the science done in the lab and the technology involved in doing it. In addition, the PI continued to be involved in the Young Women’s Summer Institute, which is a competitive program across Ohio for middle school girls, held on the Kent State University Campus. During this program, middle school girls are exposed to science experiments and interact with female scientists at different stages in their career, i.e., undergraduate and graduate students, and faculty. Graduate student Tao Hu describes to high school students the demos he is about to show them.