Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale.

Y 3Àx La x Fe 5 O 12 (x ¼ 0-0.5) ceramics with garnet structure are prepared by the solid state reaction method and their structural, magnetic, and magnetodielectric properties are investigated systematically. La 3þ substitution leads to lattice expansion and possible ion transposition, which oppositely affect the variation of Fe 2þ concentration. As a result, both the saturation magnetization and the intrinsic magnetodielectric effect first increase and then decrease with the increase of La concentration. More interestingly, room temperature large magnetodielectric coefficient of about À5% is obtained at 10 6 Hz and 0.9 T for Y 2.7 La 0.3 Fe 5 O 12 ceramics. This study provides a feasible alternative method for modulating the saturation magnetization and the magnetodielectric effect of Y 3 Fe 5 O 12 -based materials. V C 2015 AIP Publishing LLC. [http://dx.

Good ferroelectricity, weak ferromagnetism and the sign of magnetoelectric coupling are obtained simultaneously in Bi3.25La0.75(Ti2.75Fe0.125Co0.125)O12 ceramics.

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The magnetic characteristics of dilute Fe-doped SrTiO3 ceramics are studied. The room-temperature ferromagnetism (with transition temperature around 650 K) is successfully realized in Sr0.98Ti0.9Fe0.1O3−δ and Sr0.98Ti0.92Fe0.1O3−δ ceramics. It is found that a fine-tuning of the components could alter the substitution sites of Fe ions and in-turn modulates the magnetism of the material. A systematic analysis reveals that the co-substitution of Fe ions at nonequivalent A and B sites in ABO3 type perovskites is in favor of the ferromagnetism, which could be attributed to the mixed-valence-states of Fe ions and the variation of exchange interactions. This work provides an innovation for the induction and control of ferromagnetism in dilute magnetic materials.