IMF2017

The practical applications of Magnetoelectric (ME) materials essentially require a strong linear coupling between the magnetization (M) and ferroelectric polarization (P) at room temperature. BiFeO₃ is unique amongst various magnetoelectric multiferroics, as its ferroelectric and magnetic transition temperatures (T_C~1103 K, T_N~ 643 K) are well above the room temperature. In recent years, (1-x)BiFeO₃-(x)BaTiO₃ (BF-xBT) solid solutions have received considerable attention due to large ferroelectric polarization, large remnant magnetization, linear magnetoelectric coupling and highest depolarization temperature (T_d) for piezoelectric applications. However, the ground state of neither BiFeO₃ nor BF-xBT is still not clear. We present here results of Rietveld analysis of x-ray and neutron powder diffraction data in conjunction with results of magnetization, AC susceptibility and specific heat measurements. Our results reveal presence of two spin glass (SG) phases below room temperature both of which coexist with the long range ordered (LRO) antiferromagnetic (AFM) phase formed well above room temperature at the Neel transition temperature. It is shown that both the spin glass transitions are accompanied with decrease in the ordered magnetic moment and strong magnetoelastic coupling suggesting that the LRO-AFM and SG transitions occur on the same magnetic sublattice in agreement with theoretical predictions for Heisenberg systems. We also present a magnetic phase diagram of the BF-xBT system.