Extremely clean sputtering process for spin valves: Exchange anisotropy and spin-dependent transport

The extremely clean sputtering process (XC process) was newly introduced in the fabrication of ultra-thin spin valves to control the microstructure and to establish the excellent magnetic properties. The relation between cleanness during film deposition process and the magnetic properties of spin valve elements has been discussed in connection with their microstructure. As results we found that (1) the purification of the sputtering atmosphere facilitates the growth of grains; (2) the enlargement of the antiferromagnetic grains in the XC processed films enhances the exchange anisotropy at room temperature; and (3) the reduction of the grain boundaries, impurities, and defects in the XC processed spin valves results in the reduction of saturated resistivity and the enlargement of the magnetoresistance (MR) ratio. The spin valve with 9.7% of the MR ratio even in the total thickness of 148 angstroms except for the capping Ta layer was realized under the XC process.