Role of pentagon spin frustration in magnetoelectric Bi2Fe4-xCoxO9 (0 ≤x ≤ 0.8)

Abstract

Geometrically frustrated systems have attracted considerable interest because the spin frustration leads to exceptionally rich physical properties ranging over spin-liquid, quantum phase transition, anomalous large thermoelectric response and magnetoelectric (ME) properties. Recently, the spin-driven ferroelectricity due to triangular spin frustration has been observed in various antiferromagnetic compounds Ni3V2O8, hexagonal RMnO3, CuCrO2, and AgCrO2. But the role of pentagon spin frustration on the spin driven ferroelectricity is poorly understood. Bi2Fe4O9 belongs to rare class of compounds where ferroelectricity is being observed due to spin frustration in pentagon symmetry. But the microscopic picture of pentagon spin frustration is still under debate. Here, we report the preparation of magnetoelectric Bi2Fe4O9 and Co doped Bi2Fe4O9 by solid state route using bismuth oxide (Bi2O3), iron oxide (Fe2O3) and cobalt oxide (Co3O4). Our X-ray diffraction (XRD) results confirm that there is no change in crystal structure due to Co doping. Scanning Electron Microscopy image shows grain size increases due to doping which is in agreement with XRD analysis. From dielectric constant measurement we conclude that dielectric constant increases due to Co doping. UV-Visible plot shows due to Co doping band gap energy decreases.