Magnetic and dielectric properties of A2CoSi2O7 (A=Ca, Sr, Ba) crystals
Abstract
We have investigated the magnetic and dielectric properties of A2CoSi2O7 (A=Ca, Sr, and Ba) crystals with a two-dimensional network of CoO4 and SiO4 tetrahedra connected with each other through the corners. In Ca2CoSi2O7, 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; (H)/ (0) [ (H)- (0)]/ (0) reaches 13 % at 5.1 K\@. These results indicate a strong coupling between the magnetism and dielectricity in Ca2CoSi2O7. Sr2CoSi2O7 shows a similar magnetoelectric behavior to that of Ca2CoSi2O7. In contrast, in Ba2CoSi2O7, which has the different arrangement of SiO4 and CoO4 tetrahedra from that of Ca2CoSi2O7, the magnetocapacitance is hardly observed. The key for the magnetocapacitance effect of A2CoSi2O7 lies in the quasi-two-dimensional crystal structure.