Magnetisation and neutron scattering studies of multiaxial magnetic ordering in USbsub(0.9)Tesub(0.1)

Numerous experimental investigations have shown that when small amounts of the uranium chalcogenides are substituted into the uranium monopnictides, complex magnetic structures are formed. USb is a simple type I antiferromagnet, but USbsub(0.9)Tesub(0.1) shows most unusual behaviour. Studies have been undertaken on single crystals in an attempt to understand this behaviour. Below Tsub(N) 203 +- 2 K an ordering takes place with a wavevector that is nearly commensurate. At 160 K a first-order phase transition occurs to a commensurate phase. Magnetisation measurements in this phase give a saturated moment of 0.92μsub(B)/U atom, which is a factor of three less than that found for USb. The easy axis is <111>; the moments in the other principal directions are given by the cosine law. The only magnetic structure compatible with the present measurements is one described by three square-wave components propagating along the cube edges simultaneously. The resultant magnetic moment is in a <111> direction, but the exact direction of the moment varies through the lattice. This unusual magnetic structure suggests that the crystal field gives a <111> easy direction and that anisotropic exchange interactions determine the commensurate k vector. Finally, these results shed some doubt on the interpretation of the magnetic structures of the uranium monopnictides such as USb and UAs. (author)