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LaAlO3 single crystals were doped with transition element Mn by thermal diffusion method for investigation of ferromagnetism. With increasing the annealing temperature TN, ferromagnetism begins to appear when TN equals 750 °C, which is indicated by small magnetic hystersis (M ‐H) loop with low coercive field of 60 Oe measured at 60 K. After TN arrives at 1300 °C, obvious M ‐H loop can be observed at 60 K and the M ‐T curve displays sharp Curie phase transition, which shows an unambiguous ferromagnetism. A bound magnetic polaron model was proposed to understand the observed ferromagnetic behavior in Mn‐doped LaAlO3 single crystals. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The exchange bias in BiFeO 3 /La 0.67 Sr 0.33 MnO 3 (BFO/LSMO) bilayers has been investigated. Exchange bias field with blocking temperature of about 150 K and enhanced coercivity at room temperature has been observed in (001) BFO/LSMO bilayers. The blocking temperature coincides well with the emerging temperature of the vertical magnetization shift due to the blocking of the possible interfacial spin glass. Only enhanced coercivity without exchange bias field down to 10 K has been observed in (111) BFO/LSMO bilayers. The piezoelectric force microscopy images show that the domain size of (111) BFO is 2 orders larger than that of the (001) BFO, indicating the much higher domain wall density in (001) BFO. Our results demonstrate that the exchange coupling with interfacial spin glass at the domain walls contributes to the exchange bias field with blocking temperature of about 150 K, while the exchange coupling with the domains contributes to the enhanced coercivity up to room temperature.