Disorder effects in the S=1 antiferromagnetic spin ladder CaV₂O₄

We study the physical properties of the antiferromagnetic spin ladder CaV₂O₄ (CVO) and the Y-doped related compound Ca_0.9Y_0.1V₂O₄. In the latter, X-ray diffraction demonstrates the segregation of a small amount of a vanadium-perovskite impurity phase, leading to the formation of V vacancies within the main CVO-type structure. The 1D character of this calcium-vanadite enhances the influence of the vacancies on the electric and magnetic properties of Ca_0.9Y_0.1V₂O₄. Electrical transport is characterized by a variable-range hopping mechanism determined by the charging energy of nm-sized segments of V chains delimited by V vacancies, i.e. a Coulomb gap is formed at the Fermi level. These vacancies also locally affect the magnetic correlations, breaking the long-range AFM order observed in CaV₂O₄ and producing exchange bias when the Y-doped sample is cooled with an applied magnetic field.