Growth and magnetic property of $ζ$-phase $Mn2N1±x$ thin films by plasma-assisted molecular beam epitaxy

$ζ$-phase manganese nitride films were directly grown on sapphire substrates using plasma-assisted molecular beam epitaxy. $Mn2N1.06$⁠, $Mn2N0.98$⁠, and $Mn2N0.86$ films were synthesized by controlling the temperature of the effusion cell filled with highly pure manganese powder. The composition, structure, and morphology of the films were identified by x-ray photoelectron spectroscopy, x-ray diffraction and atomic force microscopy, and the magnetic properties of the films were characterized by a superconducting quantum interference device magnetometer at 5 and 300 K. The magnetic measurements reveal that $Mn2N1±x$ exhibits weak ferromagnetism at 5 K, which is mainly ascribed to the weak interaction among the Mn cations induced by the nitrogen vacancies. Furthermore, the $Mn2N0.86$ single-crystalline films are found to have room-temperature ferromagnetism, which is attributed to the strain of the $Mn2N0.86$ films raised from lattice mismatch between the $Mn2N0.86$ films and the substrates.