SmNi4B:: A narrow domain-wall ferromagnet

We have investigated magnetic properties of SmNi4B. The material undergoes a ferromagnetic ordering at T(C)approximate to 39 K, which, surprisingly, is higher than that of isostructural GdNi4B (approximate to 36 K). The saturation magnetic moment is rather small (0.15 mu(B) per Sm at 5 K), suggesting the presence of crystal-field effects. Below T-C, the material exhibits a large thermomagnetic irreversibility and also a large magnetic hysteresis at 5 K with a coercive field approximate to 28 kOe, which is one of the largest observed in a Sm-based material. We suggest that the large coercive field is intrinsic, associated with narrow domain walls of thickness of only one atomic layer, which resembles a ferroelectric wall. (C) 2000 American Institute of Physics. [S0003-6951(00)04229-7].