Magnetic transition at ∼150 K in nanoscale BiFeO3

From the high resolution powder neutron diffraction data, we obtain an evidence of spin-reorientation type transition around ∼150 K in nanoscale BiFeO3. The magnetic phase forms at ∼150 K, as a result of canting of the spins away from c-to a-axis by ∼6°, has been modeled by considering two antiferromagnetic phases of propagation vectors k = (0, 0, 0) and (0, 1/4, 1/4) and moments aligned along c- and a-axes. Direct magnetic measurement too, under both 0 and 50 kOe field, offers evidence for such a transition. While the experiment on a single crystal does not offer any evidence of magnetic transition at ∼150 K [M. Ramazanoglu et al. Phys. Rev. B 83 (2011), art. 174434(1-6)], clear observation of the transition in nanoscale BiFeO3 implies crucial role of the antiferrodistortive rotation of FeO6 octahedra, associated with large magnetization and enhanced canting angle, in inducing the transition. The transition is found to have a significant influence on the crystallographic parameters too, including the structural noncentrosymmetry which show distinct anomaly around 150 K.