Multiferroic materials are currently the subject of intensive research worldwide, because of both their fundamental scientific problems and also possible technological applications. Among a number of candidates in the laboratories, compounds consisting of rare earth and transition metal perovskite oxides have very unusual structural and physical properties. In contrast to the so-called type I multiferroics, ferroelectricity may be induced by magnetic ordering or by applying external fields. In this review, the recent progress on the experimental and theoretical studies of some selected type II multiferroics is presented, with a focus on the perovskite oxides containing rare earth and transition metal elements. The rare earth orthoferrite crystals, rare earth titanate strained film, and rare earthbased superlattices are systematically reviewed to provide a broad overview on their promising electric, magnetic, and structural properties. The recent experimental advances in single-crystal growth by optical floating zone method are also presented. First-principles investigations, either supported by experimental results or awaiting for experimental verifications, are shown to offer useful guidance for the future applications of unconventional multiferroics.
A systematic study on the structural,magnetic,and electrical transport properties was performed for the LaMn1-xCuxO3 system.A single phase of orthorhombic perovskite structure was formed for x = 0.05-0.40.A striking paramagnetic-ferromagnetic transition and a considerable magnetoresistance effect were observed at the ferromagnetic ordering temperature TC,but no insulator-metal transition induced by Cu-doping was observed.Below TC,a visible unexpected drop was observed in the ac susceptibility and zero-field-cooled dc magnetization for the dilute doped samples with x ≤ 0.10,which was proven to be associated with domain wall pinning effects by milling the bulk material into single domain particles.It is validated that there is no exchange interaction between Cu and Mn,and double exchange interactions between Mn3+ and Mn4+ are induced by Cu-doping in the anti-ferromagnetic LaMnO3 matrix,whereas the severe distortion and disorder caused by occupied-dopant prohibits charge carriers from hopping.
