Resonant x-ray and neutron diffraction study of USb_0.8Te_0.2

Complementary neutron and magnetic x-ray scattering experiments have been performed on the pseudobinary compound USb0.8Te0.2. Both techniques reveal a succession of magnetic phases on cooling. On passing through the Neel temperature (T-N similar to 205 K), the system enters an antiferromagnetic (AF) state of modulation wave vector q similar to 0.4 reciprocal lattice units. Cooling further a second AF modulation (q similar to 0.2) appears which coexists with the q similar to 0.4 modulation over a narrow range of temperature. The appearance of the q similar 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 with the emerging ferromagnetism. At the lowest temperatures studied, however, the system is found to be a saturated ferromagnet with no AF component. In the case of the x-ray study the onset of ferromagnetism is inferred from the concomitant distortion of the charge lattice. The smallest value of the magnetic peak width in the AF phase was always larger than the width of the neighboring lattice peak, consistent with finite-size effects in the ordered antiferromagnetism. Above T-N critical scattering is observed in the paramagnetic phase by both techniques. The x-ray critical scattering may be described by a single (Lorentzian) 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.