Octupole ordering in filled-skutterudite SmRu4P12

By nuclear specific heat measurements in the anomalous ordered phase of SmRu4P12, the size of the ordered Sm dipole moment m(Sm) has been determined accurately. The strongly reduced value of m(Sm) agrees perfectly with a mean-field model calculation, providing evidence that the dipole moments appear as a secondary order parameter in an octupole ordering. In the quite rare examples of octupole ordering in NpO2 and Ce1-xLaxB6, no dipole moments are induced. In this sense, the ordered state in SmRu4P12 provides a new example of octupole ordering with such unprecedented character. (C) 2007 Elsevier B.V. All rights reserved.