Dramatic effect of A-site substitution upon the structure and magnetism of the "114" CaBaCo4O7 cobaltite

Electron and hole doping at the cobalt sites of CaBaCo4O7 has been successfully realized by heterovalent substitution on A sites (Ln at Ca sites and K at Ba sites) with a narrow range. Both electron and hole doping have a dramatic impact upon the structure and magnetism, decreasing the orthorhombic distortion and weakening considerably the ferrimagnetism at the benefit of magnetic frustration. The hole doping very drastically kills the ferrimagnetism of the parent phase leading to a cluster-glass phase at lower temperatures, whereas the electron doping with a smaller cation like yttrium leads to an admixture of cluster and spin glass along with the preservation of weak ferrimagnetism. The frequency dependence of the peak position in. chi' (T) curves was quantitatively analyzed using the power law, tau = tau(0)(T-f/T-g - 1)(-zv). Moreover, the electron doping with larger lanthanides (Pr and Nd) leads to spin-glass states, which are manifested at two temperatures vis-a-vis similar to 60 K and similar to 110-115 K. The appearance of magnetic frustration at the expense of ferrimagnetism in both cases is interpreted as the result of deviation of the Co2+/Co3+ ratio from unity and cationic disordering on cobalt sites, even if the crystal remains orthorhombic.