Co ∕ Pt multilayers with large coercivity and small grains

Abstract

Multilayers of [Co∕Pt]20, with tCo∕tPt≐7 and the period Λ in the range of 0.27–0.69nm, and [Co(0.46nm)∕Pt(0.07–0.14nm)]20 have been prepared by sputtering at low deposition rates and a high Ar pressure of 7.8Pa. Structure and magnetic properties were characterized by x-ray diffraction, transmission electron microscopy, magnetometry measurements, and magnetic force microscopy. Column structure, coherent stacking of Co and Pt layers, and small grains have been observed. The average atomic interplane distance d111 changes with the constituent layer thickness. In the first series of Co∕Pt multilayers, the out-of-plane coercivity gradually increases to reach a maximum, with the bilayer period increasing from 0to0.58nm, and decreases with further increasing period. For the second series, the out-of-plane coercivity increases to reach a maximum of 6.5kOe with tPt increasing from 0.07to0.13nm and decreases with further increasing tPt. In order to explain the strong magnetic perpendicular anisotropy, the magnetoelastic energy of CoPt alloy layers must be taken into account.