NEUTRON-DIFFRACTION STUDY OF QUADRUPOLAR ORDER IN TMTE - FIRST EVIDENCE FOR A FIELD-INDUCED MAGNETIC SUPERSTRUCTURE

The intriguing phase transition discovered recently in TmTe at T-Q = 1 .8 K is characterized as antiferroquadrupolar by neutron diffraction. In an applied magnetic field, the underlying ordered structure of the Tm quadrupole moments is disclosed by the appearance of an antiferroma gnetic component of the magnetic dipole moments. This induced structur e is described by the wave Vector k = (1/2, 1/2, 1/2) for both field d irections H parallel to (111) and H parallel to (001), but the stagger ed component mu(AF), oriented along a twofold cubic axis normal to the field, is much stronger (about 1.5 mu(B)) in the former case.