STRUCTURAL AND MAGNETIC-PROPERTIES OF THE RARE-EARTH IRON NITRIDE SOLUTION SERIES Y2(FE1-XCOX)17N3-DELTA

Interstitial ternary nitrides Y2(Fe(1-x)Co(x))17N3-delta have structures related to the hexagonal Th2Ni17 structures of the parent Y2(Fe(1-x)Co(x))17 compounds. Nitrogen uptake varies with cobalt concentration from delta = 0.4 at the iron rich end (x = 0) to delta = 1.4 with increasing cobalt concentration. Unit cell volumes are typically 5% greater in the nitrides. The 3d sublattice anisotropy is modified upon nitrogenation, the transition from easy plane to easy axis shifting from x almost-equal-to 0.5 in Y2(Fe(1-x)Co(x))17 to x - 0.15 in Y2(Fe(1-x)Co(x))17N3-delta. The room temperature saturation magnetisation is greatest when x almost-equal-to 0.2 with a value of 170(4) J/(T/K g). Increasing the cobalt content raises the process temperature required to produce the Y2(Fe(1-x)Co(x))17N3-delta phase. For x greater-than-or-equal-to 0.85 the nitrogen absorption temperature is higher than the disproportionation temperature of the Y2(Fe(1-x)Co(x))17N3-delta-phase, thus no 2:17: N phase is observed in the range 0.85 < x < 1.O.