  The dielectric behavior of the single crystals of the spin-chain system
Ca3Co2O6, undergoing geometrically frustrated antiferromagnetic ordering below
25 K, has been investigated as a function of temperature and magnetic field (H)
and compared with magnetization (M) behavior. The results provide evidence for
anisotropic magnetodielectric (MDE) coupling in this compound. Ac
susceptibility exhibits a strong frequency dependence for H parallel c with
changes of this feature with the application of external dc magnetic field. No
feature in ac susceptibility could be observed for H perpendicular c, thereby
providing evidence for strong anisotropic spin-glass behavior. Interestingly,
the strong frequency dependence in dielectric is present for both the
crystallographic directions (E parallel c and E perpendicular c where E is the
electric field) with a negligible influence of H, despite the existence of MDE
coupling. This result appears to suggest different dynamics of electric dipole
and spin-glass, although they are coupled with each other. In addition,
interestingly, there is also a step at one-third of high-(magnetic) field value
of MDE at some temperatures tracking a similar step in M(H). This work also
confirms following unusual features reported on polycrystals, when measured
along c-axis. The dielectric constant exhibits a broad peak around 50-130 K
when the electric field is applied along the spin-chain (crystallographic c
direction); however this feature is essentially absent for the perpendicular
orientation. This finding supports the role of incipient spin-chain ordering to
induce magnetodielectric coupling. There is a signature of magnetoelectric
phase coexistence when the magnetic field is applied along the spin-chain
irrespective of the direction of applied electric field.
