Magnetic and dielectric properties of A2CoSi2O7 (A=Ca, Sr, Ba) crystals

TL;DR

This study explores the magnetic and dielectric properties of A2CoSi2O7 crystals, revealing strong magnetoelectric coupling in Ca and Sr variants due to their quasi-two-dimensional structures, with significant magnetocapacitance observed in Ca2CoSi2O7.

Contribution

It demonstrates the relationship between crystal structure and magnetocapacitance in A2CoSi2O7, highlighting the importance of two-dimensional network arrangements for magnetoelectric effects.

Findings

Ca2CoSi2O7 exhibits a weak ferromagnetic transition at 5.7 K with large magnetocapacitance.

Sr2CoSi2O7 shows similar magnetoelectric behavior to Ca2CoSi2O7.

Ba2CoSi2O7 has different tetrahedral arrangements and negligible magnetocapacitance.

Abstract

We have investigated the magnetic and dielectric properties of $A_2$CoSi$_2$O$_7$ ($A$=Ca, Sr, and Ba) crystals with a two-dimensional network of CoO$_4$ and SiO$_4$ tetrahedra connected with each other through the corners. In Ca$_2$CoSi$_2$O$_7$, a weak ferromagnetic transition occurs at 5.7 K, where the dielectric constant parallel to the c axis shows a concomitant anomaly. The large magnetocapacitance effect is observed below 5.7 K; $\Delta \varepsilon (H)/\varepsilon (0) \equiv [\varepsilon (H)-\varepsilon (0)]/\varepsilon (0)$ reaches 13 % at 5.1 K\@. These results indicate a strong coupling between the magnetism and dielectricity in Ca$_2$CoSi$_2$O$_7$. Sr$_2$CoSi$_2$O$_7$ shows a similar magnetoelectric behavior to that of Ca$_2$CoSi$_2$O$_7$. In contrast, in Ba$_2$CoSi$_2$O$_7$, which has the different arrangement of SiO$_4$ and CoO$_4$ tetrahedra from that of Ca$_2$CoSi$_2$O$_7$, the magnetocapacitance is hardly observed. The key for the magnetocapacitance effect of $A_2$CoSi$_2$O$_7$ lies in the quasi-two-dimensional crystal structure.