Large remnant polarization and magnetic field induced destruction of cycloidal spin structure in Bi_1−xLa_xFeO₃ (0 ≤ x ≤ 0.2) Available to Purchase

We prepared a series of Bi_1−xLa_xFeO₃ (0 ≤ x ≤ 0.2) ceramics with a sol-gel method and find that both the magnetization and dielectric constant show an abrupt anomaly near a critical field H_c, which is attributed to the destruction of the cycloidal antiferromagnetic spin structure. The critical field H_c decreases substantially from ∼20 T for the x = 0 sample [Y. F. Popov et al., JETP Lett. 57, 69 (1993)] to ∼2.8 T for the x = 0.17 sample and finally to 0 T for the x = 0.2 sample at room temperature (RT). It is also found that H_c increases with decreasing temperature. The variation of H_c with La substitution and temperature can be ascribed to the change in the magnetic anisotropy and isotropic superexchange interaction, respectively. We have also discussed the magnetodielectric effects in these samples in terms of the Ginzburg-Landau theory and the spin-phonon model. Moreover, increasing the doping level of La to 0.15 greatly improves the RT leakage-current and ferroelectric (FE) properties. A RT square-shaped FE hysteresis loop with remnant polarization (2P_r) as high as ∼64 μC/cm² is obtained for the x = 0.15 sample. These results may be important for potential applications in BiFeO₃-based magnetoelectric devices.