MAGNETIC-PROPERTIES OF THE QUATERNARY INTERMETALLIC COMPOUNDS RNIBC (R = HO, DY, TB, GD, DY1-XGDX)

The structural, resistive (2 K < T < 300 K) and magnetic properties (2 K < T < 300 K, H < 80 kOe) of RNiBC (R = Ho, Dy, Tb, Gd, Dy1-xGdx [x = 0.25, 0.5, 0.75]) were investigated and compared with the structural ly related RNi2B2C series. The crystal structure is LuNiBC-type (space group P4/nmm) wherein the unit-cell a-axis parameter and volume incre ase linearly with the R3+ ionic radius as expected from the lanthanide contraction. On the other hand the c-parameter, different from that o f RNi2B2C, show a quasi-constant R-dependency. For T > 2 K, none of th e studied RNiBC is superconducting The R3+ free-ion magnetism is obser ved for T > 100 K, however, due to crystal field effects, a considerab le reduction in the saturated R3+ magnetic moments (Gd3+ is an excepti on) is observed at low T. Furthermore, their magnetic critical tempera tures, T-c, do not show a strict scaling with the de Gennes factor as expected for localized RKKY-coupled 4f-moments: in RNiBC de Gennes sca ling is satisfied for R = Er, Ho and Dy but violated for R = Tb, Gd an d Dy1-xGdx while, in contrast, T-c for RNi2B2C follows reasonably this scaling. Such a trend in the R-dependency of T-c and of the c-paramet er in RNiBC will be discussed in terms of the characteristic stacking- pattern of their RC and Ni2B2 sheets. (C) 1998 Elsevier Science B.V. A ll rights reserved.