Crystal Structure as an Origin of High-Anisotropy Field of FeCoB Films With Ru Underlayer

The origin of high uniaxial magnetic asnisotropy in FeCoB thin films was investigated by focusing on the changes in FeCo crystal distortion and alignment. The films were prepared by facing targets sputtering using Fe68.8Co27.2B4 alloy targets and examined with X-ray diffraction (XRD) analysis. Preparation of a Ru underlayer showed reduction of coercivity H-c from 130 to 14 Oe and developed remarkably high-anisotropy field H-k of 500 Oe. FeCo(110) of the FeCoB film with a Ru underlayer revealed an oblique crystal growth and a preferred orientation in the film plane that possessed (110) [110] along the easy axis. FeCo(110) lattice spacing has 0.5% expansion along the easy axis, which induces that the magnetoelastic energy E-elastic of 3.8 x 10(5) erg/cm(3) exists along the easy axis due to an inverse magnetostriction effect. The estimated Hk from the E-elastic was 470 Oe, which corresponded well with the measured H-k of 500 Oe. This indicates that the strain in FeCo lattice is the origin of the remarkably high magnetic anisotropy.