Magnetic properties of the quaternary intermetallic compounds RNiBC (R=Ho, Dy, Tb, Gd, Dy 1− xGd x)

Abstract

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, Dy 1− x Gd x [ x=0.25, 0.5, 0.75]) were investigated and compared with the structurally related RNi 2B 2C series. The crystal structure is LuNiBC-type (space group P4/nmm) wherein the unit-cell a-axis parameter and volume increase linearly with the R 3+ ionic radius as expected from the lanthanide contraction. On the other hand the c-parameter, different from that of RNi 2B 2C, show a quasi-constant R-dependency. For T>2 K, none of the studied RNiBC is superconducting. The R 3+ free-ion magnetism is observed for T>100 K, however, due to crystal field effects, a considerable reduction in the saturated R 3+ magnetic moments (Gd 3+ is an exception) is observed at low T. Furthermore, their magnetic critical temperatures, 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 scaling is satisfied for R=Er, Ho and Dy but violated for R=Tb, Gd and Dy 1− x Gd x while, in contrast, T C for RNi 2B 2C follows reasonably this scaling. Such a trend in the R-dependency of T C and of the c-parameter in RNiBC will be discussed in terms of the characteristic stacking-pattern of their RC and Ni 2B 2 sheets.