Frustrated antiferromagnetism in bulk Ti-doped BiFeO$_3$ ceramics

We present here a magnetic characterization of Ti-doped BiFeO$_3$ prepared by a ceramic route. A detailed analysis of the microstructure revealed that Ti$^{+4}$ is not homogeneously distributed but partially segregated towards Ti enriched grain boundary regions that define Ti-deficient domains with a size distribution of the order of tens of nanometers. Since the size of these domains is smaller than the spin cycloid wavelength (64 nm) they hold a net magnetic moment. Consequently the material exhibits frustrated antiferromagnetism with hysteresis, coercivity and remanance. This ferromagnetic-like behavior vanishes at the Neel temperature of the BiFeO$_3$. The small magnetic moment per domain (M$_{\mathrm{S}}$ $\sim$0.2 emu/g) yields very large coercive fields of 27 KOe at 5 K and 17 KOe at room temperature.