Suppression of phase transitions at low temperature by chromium substitution in vanadium spinel Fe(V sub(1-x)

Synchrotron powder diffraction, magnetization, and specific heat measurements have been used to investigate the structural and magnetic phase transitions in the spinel-type vanadate Fe(V sub(1-x)Cr sub(x)) sub(2)O sub(4) (0.0 x 1.0). We observed five different transitions in our polycrystalline samples. The canted-type ferrimagnetic phase transition accompanied by the lattice distortion was suppressed by Cr substitution (x = 0.2). Additionally, high-resolution synchrotron powder diffraction revealed that the low-temperature orthorhombic phase appears in FeV sub(2)O sub(4) below 30 K and disappears by subtle Cr doping. In contrast, for x 0.7, we observed a different magnetic transition of possibly conical-type ferrimagnetic ordering that did not induce significant lattice distortion at the transition temperature. We performed structural refinements for low-temperature phases and suggest that the crystal system of Fe(V sub(1-x)Cr sub(x)) sub(2)O sub(4) at 15K is an orthorhombic lattice for all x values. In the orthorhombic phase, a unique behaviour was observed, with the lattice constants a and b approaching each other as Cr doping increased. This behaviour can be explained by the change of orbitally ordered states of the Fe super(2+) ions.