RESONANT X-RAY AND NEUTRON-DIFFRACTION STUDY OF USB0.8TE0.2

Complementary neutron and magnetic x-ray scattering experiments have b een performed on the pseudobinary compound USb0.8Te0.2. Both technique s reveal a succession of magnetic phases on cooling. On passing throug h the Neel temperature (T-N similar to 205 K), the system enters an an tiferromagnetic (AF) state of modulation wave vector q similar to 0.4 reciprocal lattice units. Cooling further a second AF modulation (q si milar to 0.2) appears which coexists with the q similar to 0.4 modulat ion over a narrow range of temperature. The appearance of the q simila r to 0.2 scattering coincides with the onset of ferromagnetic (q = 0) order in the sample. The antiferromagnetic q similar to 0.2 modulation persists over a significant range of temperature in a mixed state wit h the emerging ferromagnetism. At the lowest temperatures studied, how ever, the system is found to be a saturated ferromagnet with no AF com ponent. In the case of the x-ray study the onset of ferromagnetism is inferred from the concomitant distortion of the charge lattice. The sm allest value of the magnetic peak width in the AF phase was always lar ger than the width of the neighboring lattice peak, consistent with fi nite-size effects in the ordered antiferromagnetism. Above T-N critica l scattering is observed in the paramagnetic phase by both techniques. The x-ray critical scattering may be described by a single (Lorentzia n) function corresponding to a single correlation length, in contrast to recent observations on several other systems. The results obtained in the neutron and x-ray experiments are compared and discussed.