Simultaneous tuning of the magnetic anisotropy and thermal stability of [Formula: see text]-phase Fe[Formula: see text]N[Formula: see text].

Simultaneously enhancing the uniaxial magnetic anisotropy ([Formula: see text]) and thermal stability of [Formula: see text]-phase Fe[Formula: see text]N[Formula: see text] without inclusion of heavy-metal or rare-earth (RE) elements has been a challenge over the years. Herein, through first-principles calculations and rigid-band analysis, significant enhancement of [Formula: see text] is proposed to be achievable through excess valence electrons in the Fe[Formula: see text]N[Formula: see text] unit cell. We demonstrate a persistent increase in [Formula: see text] up to 1.8 MJ m[Formula: see text], a value three times that of 0.6 MJ m[Formula: see text] in [Formula: see text]-Fe[Formula: see text]N[Formula: see text], by simply replacing Fe with metal elements with more valence electrons (Co to Ga in the periodic table). A similar rigid-band argument is further adopted to reveal an extremely large [Formula: see text] up to 2.4 MJ m[Formula: see text] in (Fe[Formula: see text]Co[Formula: see text])[Formula: see text]N[Formula: see text] obtained by replacing Co with Ni to Ga. Such a strong [Formula: see text] can also be achieved with the replacement by Al, which is isoelectronic to Ga, with simultaneous improvement of the phase stability. These results provide an instructive guideline for simultaneous manipulation of [Formula: see text] and the thermal stability in 3d-only metals for RE-free permanent magnet applications.