TEM characterization of Co-Al-O nano-granular TMR film

Co-Al-O film was fabricated using the reactive r.f. magnetron sputtering technique. A maximum magnetoresistance (MR) of approximately 7% was established through optimizing the sputter deposition conditions such as sputter power and gas flow rate. TEM characterization of the film revealed a nano-granular structure that consisted of ferromagnetic grains with grain diameters on the order of several nm together with non-magnetic grain boundary layers with the thickness on the order of less than 1 nm. The large MR was attributed to electron tunneling thorough this very thin grain boundary layer between individual ferromagnetic grains.