  CaBaCo4O7 represents a new class of ferrimagnets whose structure is built up
of CoO4 tetrahedra only, similarly to other members LnBaCo4O7 of the 114
series, forming an alternate stacking of kagome and triangular layers. Neutron
powder diffraction reveals, that this compound exhibits the largest distortion
within the 114 series, characterized by a strong buckling of the kagome layers.
Differently from all other members it shows charge ordering, with Co2+ sitting
on two sites (Co2, Co3) and mixed valent cobalt Co3+/Co2+L sitting on two other
sites (Co1, Co4). The unique ferrimagnetic structure of this cobaltite at 4 K
can be described as the assemblage of ferrimagnetic triple chains (Co1 Co2 Co3)
running perpendicular to the kagome layers, ferromagnetically coupled within
the layers, and antiferromagnetically coupled with a fourth cobalt species Co4.
The lifting of the geometrical frustration towards ferrimagnetism, which
appears in spite of the triangular topology of the cobalt lattice, is explained
by the very large structural distortion, charge ordering phenomena and large
cobalt valence compared to other LnBaCo4O7 oxides.
