L.R. Shi

Exchange bias effect in Bi2Fe3AlO9 ceramics

The exchange bias (EB) effect is observed in Bi2Fe3AlO9 polycrystalline ceramics. The EB field (HEB), vertical magnetization shift, and coercive field show a strong dependence on the cooling fields. When a larger applied field is used to measure the hysteresis loop, the EB effect is suppressed. The induced spin-glass-like phase via Al3+ doping is responsible for the EB effect below the spin-glass temperature (TSG) of ∼25 K. Moreover, the HEB varies nonmonotonically with temperature above TSG, which is interpreted using a random field model with the exchange coupling between ferromagnetic clusters and an antiferromagnetic phase.

Al3+ doping effects and high-field phase diagram of La0.5Sr0.5Mn1−x Al x O3

Magnetization measurements of La0.5Sr0.5Mn1−x Al x O3 (0 ≤ x ≤ 0.25) under pulsed high magnetic fields up to 50 T have been carried out, in which the Al3+ ions doping and magnetic field effects on the charge-ordering/antiferromagnetic to ferromagnetic phase transitions have been discussed. A triple-phase diagram with the critical field, doping level and temperature has been determined, in which the antiferromagntic and ferromagnetic phase boundaries were clearly defined. The change from long-range charge-ordered/antiferromagnetic phases to the robust short-range ones upon the Al3+-doping was observed. According to the experimental results, we assume that Al3+ ion doping at the Mn sites dilutes the Mn3+-O-Mn4+ network, weakens the double-exchange interaction and further suppresses the FM phase (metallic conduction), which leads to the critical magnetic fields destroying the antiferromagnetic order increase with the increase of the doping level.