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We have fabricated biocompatible nanofiber hydrogels with diverse sizes of ferritin clusters according to the mixing temperature of solutions employing electrospinning. Poly(vinyl alcohol) (PVA) was used as a polymeric matrix for fabricating nanocomposites. By thermal means we controlled the interaction between the host PVA hydrogel and the protein shell on ferritin bionanoparticles to vary the size and concentration of ferritin clusters. The clustering of ferritin was based on the partial unfolding of a protein shell of ferritin. By studying the magnetic properties of the PVA/ferritin nanofibers according to the mixing temperature of the PVA/ferritin solutions, we confirmed that the clustering process of the ferritin was related to changes in the superparamagnetic properties and magnetic resonance imaging (MRI) contrast of the PVA/ferritin nanofibers. PVA/ferritin nanofiber hydrogels with diverse spatial distributions of ferritin nanoparticles are applicable as MRI-based noninvasive detectable cell culture scaffolds and as artificial muscles because of their improved superparamagnetic properties.

The microstructural and the magnetotransport properties of La 0.7 Ca 0.3 MnO 3 and La 0.7 Sr 0.3 MnO 3 films, deposited on a BaTiO 3 layer ͑LCMO/BTO and LSMO/BTO, respectively͒, and on LaAlO 3 and SrTiO 3 ͑001͒ single crystals ͑LCMO/LAO, LSMO/LAO and LSMO/STO͒ by rf-magnetron sputtering using the "soft" ͑or powder͒ targets, have been investigated. The films grown on BTO demonstrate biaxial tensile in-plane and compressive out-of-plane strains, while those grown on LAO show the opposite trend, i.e., compressive in-plane and tensile out-of-plane strains. The films with a biaxial tensile in-plane strain undergo the magnetic transition at a higher temperature than those with a biaxial compressive one. This implies that the variation of Mn-O-Mn bond angle, controlled by the lattice strain, plays a more important role in the formation of spin ordering in the manganite film than the modification in the Mn-O bond length does. It was shown that the magnetic inhomogeneity, observed through the difference between field-cooled and zero-field-cooled temperature-dependent magnetization, is not greatly relevant to the electronic nature, but is controlled by the lattice distortion and the microstructural defects. The observed enhancement of magnetoresistance for the LSMO/BTO bilayer at room temperature makes this material system promising in the development of new hybrid ferromagnetic/ferroelectric devices.

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The microstructure and the magnetic properties of La0.4Ca0.6MnO3 film, prepared by rf magnetron sputtering on a LaAlO3 substrate, have been investigated. The electron microscopy study reveals the presence of strip-domain phase with a periodic spacing of about 3c for the orthorhombic symmetry. The magnetic measurements show that in addition to the expected antiferromagnetic transition at TN≃120 K with decreasing temperature, the film manifests the Griffiths phase behavior in a wide temperature range.