Tailoring the interfacial exchange coupling of perpendicularly magnetized Co/L10-Mn1.5Ga bilayers

Abstract

We have studied the magnetic properties of Co (2–12 MLs)/L10-Mn1.5Ga (15 nm) bilayers without and with annealing at 300 °C by a combination of superconducting quantum interference device (SQUID) magnetometry and x-ray magnetic circular dichroism (XMCD). We find that the Co layer can remain perpendicularly magnetized when its thickness is less than six monolayers due to the coupling between Co and L10-Mn1.5Ga layers, which is doubly confirmed by both SQUID and XMCD measurements. Such an exchange coupling between L10-Mn1.5Ga and Co layers changes from ferromagnetic coupling to antiferromagnetic coupling after the annealing process. Furthermore, the magnetic coupling can also be tailored from ferromagnetic to antiferromagnetic by changing the L10-Mn1.5Ga surface from Mn-rich to Ga-rich. The first-principles calculations show that the interfacial coupling type is ferromagnetic for a Mn-terminated L10-Mn1.5Ga bilayer, while antiferromagnetic for a Ga-terminated bilayer. The spin and orbital moments of Co in the Co/L10-Mn1.5Ga bilayers are calculated according to the sum rules and the ratio of the orbital to spin magnetic moments for Co is not enhanced like other perpendicularly magnetized Co-based multilayers such as Co/Pd and Co/Pt.