Electric-field effects on thickness dependent magnetic anisotropy of sputtered MgO/Co40Fe40B20/Ta structures

We have investigated the effect of applied electric field E-G on thickness dependent magnetic anisotropy of sputtered Co40Fe40B20 sandwiched with MgO and Ta. The range of CoFeB thickness explored is 2 nm and below. As the thickness is reduced, the easy axis of magnetization becomes perpendicular from in-plane. We show that perpendicular magnetic anisotropy of in-plane samples and coercivity of perpendicular samples can be modified by applying E-G at room temperature. Furthermore, superparamagnetic behavior is observed for CoFeB layers with further reduced thickness below approximate to 0.9 nm, where electric-field effect is also observed below their blocking temperature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3429592]