Twist p(z) Orbital and Spin Moment of the Wavy-Graphene/L1(0)-FePd Moire Interface

A crystallographically heterogeneous moire interface of hexagonal graphene (Gr) and a tetragonal L1(0)-FePd alloy is bonded via van der Waals (vdW) forces. Robust interfacial perpendicular magnetic anisotropy was discovered at the L1(0)-FePd side of the Gr/L1(0)-FePd heterogeneous interface (H. Naganuma et al. ACS Nano, 2022, 16, 4139). This study focuses on the Gr side of the Gr/L1(0)-FePd interface. X-ray absorption spectroscopy measurements of Gr from two different angles demonstrated that in addition to the pi* orbital peak being observed at a glance incident angle (theta(A) = 30 degrees), it was also observed at a nominal incident (NI) angle (theta(A) = 90 degrees). The appearance of the pi* peak at NI is attributed to the wavy Gr and strong bonding of the chemisorption-type vdW force. The densities of states of p(x), p(y), and pz from first-principles calculations indicate another reason for the pi* peak at NI. The p(z) orbital of C twists into the x-y plane owing to its chemical bond with Fe or perturbation of the Fe ion to the C orbital. This twisted p(z) orbital appears near the Fermi level. Thus, the p* peak at NI can be interpreted to appear owing to three reasons: (i) the wavy Gr, (ii) the twisted pz orbital near the Fermi level, and (iii) the chemisorption-type vdW force. The X-ray magnetic circular dichroism of the C K-edge and first-principles calculations revealed that wavy Gr has a spin magnetic moment of 0.018 mu(B)/C atoms but no orbital magnetic moment.

Automated summary

A crystallographically heterogeneous moire interface is formed between hexagonal graphene (Gr) and tetragonal L1(0)-FePd alloy via van der Waals forces. Robust interfacial perpendicular magnetic anisotropy is observed on the L1(0)-FePd side of the Gr/L1(0)-FePd heterogeneous interface. This study focuses on the Gr side of the interface.