Magnetoelectric spin-glass transition(s) in pure and disordered BiFeO3

We present here the results of a comparative study of the spin glass (SG) transition in pure and disordered (0.80BiFeO3-0.20BaTiO3 or 0.80BF-0.20BT) BiFeO3. It is shown that the anomalous frequency dependence of ac susceptibility in the SG phase of BF is not linked with the spin cycloid as it is present even after its destruction in 0.80BF-0.20BT solid solution. Our neutron scattering studies on disordered BF reveal the presence of long-range ordered (LRO) antiferromagnetic (AFM) peak and decrease in the ordered magnetic moment from the overall Brillouin function behaviour around the SG transition suggesting that some spin components are getting detached from the AFM phase. Further, the SG transition is accompanied with anomalies in the unit cell volume and ferroelectric polarization around the SG transition temperature, highlighting the presence of magnetoelastic and magnetoelectric couplings, respectively. All these results suggest that the SG phase of BF is intrinsic to the system and is not due to nano-sized impurities.