Intrinsic Ferromagnetism and Surface Oxidation in Nb 2 FeC: Revealed by Synchrotron‐Based X‐Ray Spectro‐ and Microscopy

ABSTRACT A‐site substitution in M n+1 AX n (MAX) phases with transition metals carrying partially filled 3 d orbitals offers a pathway to induce magnetism in otherwise nonmagnetic layered carbides/nitrides. Here, we investigate Nb 2 FeC, obtained by replacing the nonmagnetic Al site in Nb 2 AlC with Fe, using synchrotron‐based spectroscopy and microscopy. Structural analysis confirms hexagonal P6 3 /mmc phase with alternating Fe and Nb 2 C layers along the c ‐axis. Surface‐sensitive X‐ray absorption reveals a thin Fe‐oxide overlayer from ambient exposure, while Fe in the bulk reveals alloying‐driven hybridization between Fe and Nb states. Magnetization measurements establish robust ferromagnetism with a Curie temperature near 283 K. Importantly, Fe L 3,2 ‐edge Scanning Transmission X‐ray Microscopy (STXM) combined with X‐ray Magnetic Circular Dichroism (XMCD) directly demonstrates intrinsic bulk ferromagnetism, even though conventional surface‐sensitive XMCD shows no signal. The STXM‐XMCD dichroic response remains nearly unchanged across regions of varying thickness, indicating that ferromagnetic (FM) correlations are confined within the two‐dimensional Fe layers and coupled only weakly across Nb 2 C spacers. Thickness‐dependent absorption spectra further reveal Fe─Nb hybridization, underscoring the role of A‐site substitution in tuning magnetic interactions. These findings identify Nb 2 FeC as a rare/near room‐temperature FM MAX phase and highlight A‐site engineering as a versatile strategy for designing layered magnetic carbides for spintronic applications.