Giant magnetoresistance spin valves exchange-biased by ferroelectric BiFeO$_3$ thin films

The recent demonstrations of electric-field-driven magnetization control in ferromagnet(FM)/BiFeO$_3$ bilayer systems [1,2] have attracted considerable interest because of the potential applications in spintronics. In this study, giant magnetoresistance (GMR) spin valves (Co/Cu/Py/Ta) were fabricated on SrRuO$_3$/BiFeO$_3$ films by magnetron sputtering at a base pressure of 2 $\times$ 10$^{-8}$ Torr and with an external field of 300 Oe. The presence of exchange bias between the BiFeO$_3$ layer and the ferromagnetic Co layer is established by magnetization and electronic transport data. The heterostructure was patterned in a rectangular shape with a width of about 20 $\mu$m and a length up to 100 $\mu$m. The GMR characteristics of the patterned devices were systematically studied and directly compared to that obtained from identically fabricated structures on NiO and SiO$_2$, respectively. How these results relate to the realization of reversible control of the GMR spin valve effect by an electric field will be discussed.\\[4pt] [1] Heron et al., Phys. Rev. Lett 107, 217202 (2011);\\[0pt] [2] Ratcliff et al., submitted].