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Dielectric anomalies and magnetodielectric coupling behavior of single crystalline Ca3Co2O6, a geometrically frustrated magnetic spin-chain system

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.