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All-spinel oxide Josephson junctions for high efficiency room temperature spin filtering

03/11/2017 - Salle S208


Spin-filtering (SF) across an ultra-thin ferromagnetic insulating barrier between two nonmagnetic electrodes can generate highly spin-polarized currents due to the preferential tunnelling of one of the two spin orientations [1].

The ferromagnetic insulating spinel ferrites (CoFe2O4, NiFe2O4, MnFe2O4) are the candidates for achieving SF at room temperature as their Curie temperatures are well above 300K [2]. However, high efficiency SF at technologically useful temperatures [3,4] has been hampered by low structural quality of the barrier due to the lack of non-magnetic electrodes with the same crystal structure and lattice parameter of these complex oxides. One of the few conducting spinels, LiTi2O4, is superconducting (critical temperature of about 13 K) and has a lattice parameter closely-lattice matched to those of the ferrites. Thus, integrating LiTi2O4 in a spin filter device could pave the road to the fabrication of a closely lattice-matched all-spinel heterostructure, attempting to largely eliminate defects within the barrier and so greatly enhance the room temperature SF efficiency.

This talk addresses the successful demonstration of the use of LiTi2O4 thin films as electrodes in an all-spinel oxide CoFe2O4-based spin filter devices. The LiTi2O4 in these tunnel junctions is superconducting and so measurements at low temperature have been used to explore details of the tunnelling and Josephson junction behaviour.

[1] J. S. Moodera, T. S. Santos, and T. Nagahama, J. Phys. Condens. Matter 19, 165202 (2007).
[2] J.-B. Moussy, J. Phys. D. Appl. Phys. 46, 143001 (2013).
[3] A. V. Ramos, M.-J. Guittet, J.-B. Moussy, R. Mattana, C. Deranlot, F. Petroff, and C. Gatel, Appl. Phys. Lett. 91, 122107 (2007).
[4] S. Matzen, J.-B. Moussy, R. Mattana, K. Bouzehouane, C. Deranlot, and F. Petroff, Appl. Phys. Lett. 101, 042409 (2012).