MAGNETIC FRUSTRATION, SPIRALS AND SHORT-RANGE ORDER IN CRXFE1-XVO4-I SOLID-SOLUTIONS

The crystal and magnetic structures of CrxFe1-xVO4-I solid solutions with x = 0.25, 0.50, and 0.75 have been investigated by neutron diffraction and magnetic susceptibility measurements. Site occupancy refinements and geometrical arguments show that there is a small degree of Cr3+/Fe3+ ordering between two inequivalent octahedral sites with increasing x, as Cr3+ preferentially occupies the site that can become more regular. Antiferromagnetic order is observed below the Neel temperature T(N) = 21.8(5) and 17.9(2) K for the x = 0.25 and 0.50 samples, respectively, and can be described by the propagation vector (0, tau-y, 1/2) where tau-y = 0.161(3) for x = 0.25 and tau-y = 0.25(1) for x = 0.50. The magnetic structures contain clusters of four antiferromagnetically coupled spins, but the order between clusters is frustrated, resulting in magnetic spirals that propagate along the monoclinic b axis. The frustration also gives rise to increasing amounts of short-range magnetic order with increasing x, such that no long-range order is observed for x = 0.75.