Towards Room Temperature Spin Filtering in Oxide Tunnel Junctions

Spin filtering, in which the magnetic tunnel barrier preferentially filters spin-up and spin-down electrons from a nonmagnetic electrode, has been demonstrated in junction heterostructures. By incorporating two spin filtering barriers, double spin filter magnetic tunnel junctions (DSF-MTJs) were predicted to yield magnetoresistance (MR) values orders of magnitude larger than that of conventional magnetic tunnel junctions. Recently, DSF-MTJs have exhibited spin filtering with magnetic electrodes at room temperature and at low temperature with nonmagnetic electrodes in EuS-based devices [1,2]. We have fabricated DSF-MTJs with nonmagnetic SrRuO$_{3}$ electrodes and room temperature ferrimagnets, NiFe$_{2}$O$_{4}$ and CoFe$_{2}$O$_{4,}$ for spin filters in pursuit of room temperature functionality. Atomic force microscopy shows smooth films quantified by roughness values between 0.1--0.5nm. X-ray magnetic circular dichroism reveals ferromagnetic Ni$^{2+}$ and Co$^{2+}$, and element-specific hysteresis loops indicate the independent switching of the two spin filters. Transport data reveals junction MR and non-linear I-V characteristics consistent with tunneling. \\[4pt] [1] M.G. Chapline et al., PRB, 74, 014418 (2006).\\[0pt] [2] G.- X. Miao et al., PRL, 102, 076601 (2009).