Onset of ferromagnetism in pseudobinary FCC (Fe_1-xNi _x)₉₂C₈ alloys. I. Magnetic phase diagram

The magnetic phase diagram of pseudobinary FCC (Fe_1-xNi _x)₉₂C₈ alloys (0.1<or=x<or=0.4) fabricated by rapid quenching has been investigated by static magnetisation, AC susceptibility and Mossbauer effect. The Pauli-type paramagnetism is found at x=0.1 and the spin glass is at 0.1<x<0.2. At 0.2<or=x<or=0.25 the weak ferromagnet coexists with the paramagnet, showing re-entrant spin-glass behaviour. The Fe magnetic moment gradually increases with increasing x from x=0.2, and reaches 2.8 mu _B (or 2.1 mu _B for Fe with the first neighbouring carbon) in the strong ferromagnet at x>or=0.25. The onset of ferromagnetism is discussed in connection with the lattice expansion due to an interstitial carbon and with the effective charge transfer from C to Fe. The magnetic phase diagram as well as the dependence of Fe magnetic moment on x is explained by the environmental effect.