Effects of digital doping with Mn in the structural and ferromagnetic properties of AlN

• Digital Mn doping induces room-temperature ferromagnetism in AlN and enhanced magnetic moments compared with conventional MBE growth. • Raman spectra show more effective Mn incorporation at Al lattice sites in samples grown by digital doping. • Digital doping growth promotes AlN nanodots confirmed by RHEED, SEM and TEM. • Nanodots modify magnetic domains, strengthening ferromagnetic interactions. We have investigated the growth of AlN doped with Mn by molecular beam epitaxy (MBE) using an alternating flux supply method, where Al and Mn fluxes are modulated while maintaining a constant nitrogen flux (digital doping growth). Vibrating sample magnetometry showed that Mn digital doping induced room-temperature ferromagnetism in AlN, with enhanced magnetic moments compared with samples grown by conventional MBE. Raman spectroscopy revealed a more pronounced local vibrational mode associated with Mn at Al sites in samples grown by digital doping, indicating a more effective Mn incorporation in cation sites. The digital growth conditions at low-temperature favored AlN nanodots formation on the surface, not observed in samples grown by conventional MBE. Nanodot formation on the surface was evidenced by chevron patterns in reflection high-energy electron diffraction (RHEED) and confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Atomic force microscopy (AFM) revealed nanodots with an average height of 4.2 nm and width of 50.3 nm. Magnetic force microscopy (MFM) showed that nanodot formation influences magnetic domain behavior, enhancing ferromagnetic interactions under applied fields. X-ray photoelectron spectroscopy (XPS) analysis provides additional evidence that Mn is predominantly incorporated at Al lattice sites within the AlN matrix, supporting substitutional Mn incorporation rather than secondary phase formation. Overall, these results highlight the combined effect of Mn digital doping and nanodot formation in promoting ferromagnetism in AlN:Mn.