Effect of Holmium substitution on the magnetic and magnetodielectric properties of multiferroic Bi2Fe4O9

Abstract

In the quest for deriving new multiferroics from the existing ones, we have prepared and studied polycrystalline Bi2(1-x)Ho2xFe4O9 (0 ≤ x ≤ 0.02) ceramics. A substantial increase in the Néel temperature (TN) from 250 K (x = 0, BFO) to 266 K (x = 0.02, BHFO2) is observed for Ho-substituted samples. The magnetization measurements suggest that Ho3+ goes as isolated magnetic defects and interaction among them is reflected only when the temperature goes below 70 K. Interestingly, the Néel temperature is not clearly visible in the magnetization-temperature plot due to its masking by the high moment of isolated Ho3+ ions, but TN is very clearly reflected in the dielectric plot, thus indicating a plausible coupling between the magnetic and electric order parameters. Also, a dielectric crossover at T ∼ 200 K is observed for Ho3+ substituted samples and explained using a mean-field approximation model, thereby validating the presence of isolated defects arising due to Ho3+ substitution. At the same time, an enhanced magnetodielectric (MD) effect at 200 K i.e., ∼−1.6% (∼530 times) for BHFO2 is discerned as compared to BFO. Furthermore, confirmation to this coupling is drawn from MD% versus T plot and MD% versus H plot, where the latter is found to obey ∝(H)m behaviour.