Local ordering and magnetism in Ga0.9Fe3.1N

Prior investigations of the ternary nitride series Ga1–xFe3+xN (0≤x≤1) have indicated a transition from ferromagnetic γ′-Fe4N to antiferromagnetic “GaFe3N”. The ternary nitride “GaFe3N” has been magnetically and spectroscopically reinvestigated in order to explore the weakening of the ferromagnetic interactions through the gradual incorporation of gallium into γ′-Fe4N. A hysteretic loop at RT reveals the presence of a minority phase of only 0.1–0.2 at%, in accord with the sound two-step synthesis. The composition of the gallium-richest phase “GaFe3N” was clarified by Prompt Gamma-ray Activation Analysis and leads to the berthollide formula Ga0.91(1)Fe3.09(10)N1.05(7). Magnetic measurements indicate a transition around 8 K, further supported by Mössbauer spectral data. The weakening of the ferromagnetic coupling through an increasing gallium concentration is explained by a simple Stoner argument. In Ga0.9Fe3.1N, the presence of iron on the gallium site affects the magnetism by the formation of 13-atom iron clusters.