Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2 FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (t CFAO), large perpendicular anisotropy field of ∼8.0kOe can be achieved at PO2 =12% for the sample of t CFAO =2.1nm or at PO2 =7% for t CFAO =2.8nm. The loss of PMA at thick t CFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.
Bibliographical noteFunding Information:
This work is supported by the National Basic Research Program of China (No. 2014CB921104), the National Natural Science Foundation of China (Grant Nos. 11474047, 51222103, 11274113, and 51171047), and the NCET Program (No. 12-0132). H. B. Zhao thanks the support of NSFC with the grant No. 61222407.