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Fe-doped (Ba 1− x Sr x )TiO 3 ceramics were prepared by solid-state reaction, and ferromagnetism was realized at room temperature. The microstructure and magnetism were modified by the Sr concentration control (0≤ x ≤75 at%) at a fixed Fe concentration, and the relevant magnetic exchange mechanism was discussed. All the samples are shown to have a single perovskite structure. When increasing the Sr concentration, the phase structure is transformed from a hexagonal perovskite into a cubic perovskite, with a monotonic decrease in lattice parameters induced by ionic size effect. The room-temperature ferromagnetism is expected to originate from the super-exchange interactions between Fe 3+ on pentahedral and octahedral Ti sites mediated by the O 2− ions. The increase in Sr addition modifies two main influencing factors in magnetic properties: the ratio of pentahedral to octahedral Fe 3+ and the concentration of oxygen vacancies, leading to a gradually enhanced saturation magnetization. The highest value, obtained for Fe-doped (Ba 0.25 Sr 0.75 )TiO 3 , is an order of magnitude higher than that of the Fe-doped BaTiO 3 system with similar Fe concentration and preparation conditions, which may indicate (Ba 1− x Sr x )TiO 3 as a more suitable matrix material for multiferroic research.

Microstructure and magnetic properties of crystalline Ce 1 Y 2 Fe 5 O 12 thin films prepared on GGG and on SiO 2 /Si substrates by pulsed laser deposition were studied. The results show that highly textured Ce 1 Y 2 Fe 5 O 12 film with (4 4 4) preferred orientation prepared on GGG (1 1 1) shows strong paramagnetism superimposed by a weak ferromagnetism. However, polycrystalline Ce 1 Y 2 Fe 5 O 12 thin films on SiO 2 /Si, which can only be obtained after post-annealing, show strong ferromagnetism with easy axis of magnetization lying in the plane of the film. With post-annealing temperature increasing, CeO 2 segregates from Ce 1 Y 2 Fe 5 O 12 ; then YIG continues to be decomposed, forming Fe 2 O 3 . Consequently, the saturation magnetization of Ce 1 Y 2 Fe 5 O 12 films decreases first and then increases correspondingly, which indicates that the magnetic properties of Ce 1 Y 2 Fe 5 O 12 films are mainly related to the microstructure.

Ba(Ti 1− x Fe x )O 3 ceramics ( x =7, 30 and 70 at%) were prepared by solid-state reaction. All samples are single-phase with 6H-BaTiO 3 -type hexagonal perovskite structure. Mossbauer spectra show all Fe atoms to be present as Fe 3+ in BaTiO 3 lattice, occupying M 1 octahedral and pentahedral sites. Room-temperature ferromagnetism is exhibited and saturation magnetization gradually decreases with increasing Fe content. The observed ferromagnetism is considered to be an intrinsic property of Ba(Ti 1− x Fe x )O 3 , originating from super-exchange interactions between Fe 3+ in different occupational sites associated with oxygen vacancies. The variation in magnetization with Fe content is related to the ratio of pentahedral to octahedral sites and oxygen vacancies.