Magnetic frustration, spirals and short-range order in CrxFe1 –xVO4–I solid solutions

Abstract

The crystal and magnetic structures of Cr_xFe_{1 –x}VO₄–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 Néel 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,τ_y, 1/2) where τ_y= 0.161(3) for x= 0.25 and τ_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.