Magnetic structure of beta-DyD2+x: Modulated phases for x=0 and short-range order for x=0.135

The magnetic transitions in the stoichiometric dideuteride beta-DyD2.00 have been studied by cold-neutron diffraction and low-field magnetization measurements. We observe, below T-2=5.0(2) K, two sinusoidally modulated configurations, one for T less than or equal to T-1, the other for T-1 less than or equal to T less than or equal to T-2, with a partial overlap of about 0.5 K between them. The transition at T-1 presents a thermal hysteresis between 2.5 and 3.5 K. The magnetic structure below T-1 is nearly commensurate, with a propagation vector close to (1/4,1/4,3/4), k(1) = (0.258,0.273,0.750), that between T-1 and T-2 is more incommensurate, with a k(2)= (0.275,0.275,0.750).The beta-DyD2.135 specimen shows no magnetic long-range order but exhibits a broad bump in its spectrum, disappearing at 4-6 K and attributed to short-range ordered domains of similar to 30 Angstrom correlation length, confirming earlier resistivity and susceptibility measurements.