Magnetic and dielectric properties of A2CoSi2O 7 (A=Ca, Sr, Ba) crystals

Abstract

We have investigated the magnetic and dielectric properties of A 2CoSi2O7 (A=Ca, Sr, and Ba) crystals with a two-dimensional network of CoO4 and SiO4 tetrahedra connected with each other through the corners. In Ca2CoSi 2O7, 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; Δ(H)/(0) [(H) - (0)]/(0) reaches 13 % at 5.1 K. These results indicate a strong coupling between the magnetism and dielectricity in Ca 2CoSi2O7. Sr2CoSi2O 7 shows a similar magnetoelectric behavior to that of Ca 2CoSi2O7. In contrast, in Ba 2CoSi2O7, which has the different arrangement of SiO4 and CoO4 tetrahedra from that of Ca 2CoSi2O7, the magnetocapacitance is hardly observed. The key for the magnetocapacitance effect of A2CoSi 2O7 lies in the quasi-two-dimensional crystal structure. © 2009 IOP Publishing Ltd.