Enhanced anomalous Hall and negative anisotropic magnetoresistance effects driven by p-d hybridization with carbon

Co
2
Mn
2
C thin films were synthesized via vacuum carburization of the host CoMn alloy films based on a conventional gas–solid reaction to demonstrate the effect of C, a common light element, on the magnetic and spintronic materials. The crystal structure transitioned from the disordered face-centered cubic CoMn to the L1
0
-like Co
2
Mn
2
C, for which the lattice constant increased from 0.356 to 0.378 nm. The C 1s X-ray photoemission spectra of the Co
2
Mn
2
C film indicated hybridization in C–Co and C–Mn and a homogeneous concentration of C in the film. The enhancement of both the saturation magnetization and the anomalous Hall conductivity (σ
xy
) was induced by C, attributing to the magnetic transition to the ferrimagnetic spin order. The surface flatness and high σ
xy
are promising characteristics for spintronic applications such as the spin-anomalous Hall effect. Furthermore, the sign of in-plane anisotropic magnetoresistance ratio changed from positive for the host CoMn to negative for the Co
2
Mn
2
C, suggesting the inversion of dominant spins from majority-spin to minority-spin. The atomic- and spin-resolved density of states (DOS) via first-principles calculations revealed that face-centered Mn(II) and Co could be significantly influenced by C because of p–d hybridization, resulting in enhanced spin polarization of the DOS at the Fermi level of ~0.82. These results demonstrate that the use of C could be an essential way to boost material properties in the future.