  In RBaCo4O7 (R = Ca, Y and Rare earth) cobaltite family, only CaBaCo4O7 shows
3D long range ferrimagnetic and spin driven electric polarization properties.
In the present study, we have investigated the structural, magnetic and
electric polarization properties in YBaCo4O7 and DyBaCo4O7 members of this
family and the obtained results are compared with the CaBaCo4O7. The compound
YBaCo4O7 showed a series of magnetic transitions in agreement with reported
literature, additionally, a cluster glass behavior below 5 K is observed.
Powder neutron diffraction studies on DyBaCo4O7 cobaltite showed an
orthorhombic Pbn21 symmetry and signature of short-range 120 degree magnetic
correlations of kagome layer and a spin glass behavior below 65 K. Dielectric
measurements on both the samples showed strong frequency dispersion at high
temperature and frequency independent behavior at low temperature without
dielectric anomaly. Pyroelectric current measurement has showed a broad peak
around 50 K in both the samples; however, a careful analysis relates the peak
to thermally stimulated depolarization current. This study signifies that the
giant structural distortions and cobalt charge ordering at kagome layer are the
key factors to drive both long range magnetic ordering and spin driven electric
polarization in this cobaltite family.
