Phase transformation in crystal and magnetic structure and improved dielectric and magnetic properties of Ho substituted BiFeO3multiferroics

The changes in crystal and magnetic structure of BiFeO3 produced by partial substitution of Bi ions by Ho ions has been studied with powder X-ray diffraction, neutron powder diffraction, dielectric and magnetization techniques. The present study demonstrates that Bi1-xHoxFeO3(x = 0.05, 0.10, 0.15, & 0.2) multiferroics shows change in crystal structure at x > 0.05. The sample with x = 0.05 exhibits rhombohedral structure (space group R3c), while the other three samples (x > 0.05) exhibit mixed phase with coexisting rhombohedral (R3c) and Orthorhombic (Pnma) structure. This change in the crystal structure is attributed to the distortion of FeO6 octahedra via substitution of Ho at phase boundaries. The magnetization studies indicate that doping of Ho in pristine BiFeO3 leads to enhancement in the ferromagnetic moment. We find that doping of Ho breaks the spin cycloid phase of BiFeO3 and creates a canted G-type antiferromagnetic structure in the hexagonal phase whereas the orthorhombic phase exhibits a collinear G-type AFM structure. The canting angle increases with increase in doping with Ho, leading to an enhancement in the ferromagnetic component in magnetization. Dielectric constant (ε′) and loss factor (tanδ) are measured in frequency range 1 kHz to 7 MHz and ε′ and tanδ show dispersion behaviour at low frequencies. The significant improvement in magnetization and dielectric properties is achieved by Ho substitution which in turn enhances the potential of BiFeO3 for multiferroics applications.