Resistivity, magnetoresistance and field-dependent AC susceptibility of ErNiBC

Measurements are reported on the temperature and field dependence of the resistivity of ErNiBC between 1.5 and 15 K in fields up to 7 T. The zero-field resistivity displays an abrupt fall below 4.1 K and an overall character consistent with ferromagnetic ordering, as inferred from recent neutron scattering measurements; the data below 2 K can be reproduced by a model describing conduction-electron scattering by spin waves following a gapped dispersion relation: E(q) = Delta + Dq(2), with the gap parameter Delta = 2 +/- 0.5 K. Data acquired in various fixed fields can be adequately reproduced by adding a conventional Zeeman term to Delta. The field-dependent AC susceptibility does not display features normally associated with critical fluctuations at a ferromagnetic transition, although here the latter might be obscured by a substantial regular contribution, the presence of which could signify considerable magnetic anisotropy most likely to be associated with single ion spin-orbit coupling at Er sites.