We present direct evidence for room-temperature magnetization reversal induced by an electric field in epitaxial ferroelectric BiFeO3-ferrimagnetic CoFe2O4 columnar nanostructures. Piezoelectric force microscopy and magnetic force microscopy were used to locally image the coupled piezoelectric-magnetic switching. Quantitative analyses give a perpendicular magnetoelectric susceptibility of approximately 1.0 x 10(-2) G cm/V. The observed effect is due to the strong elastic coupling between the two ferric constituents as the result of the three-dimensional heteroepitaxy.

We show the importance of the role of strain in La0.7Sr0.3MnO3 films by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropy effects in the magnetic anisotropy of these films. Magnetic anisotropy measurements of (001) and (110) La0.7Sr0.3MnO3 thin films on SrTiO3 and LaGaO3 substrates, with excellent structural quality, reveal twofold symmetry on (110) La0.7Sr0.3MnO3 films and fourfold symmetry on (001) films. Such symmetries can only be explained by stress anisotropy contributions in the plane of the film. In conjunction with the thickness dependence of the magnetic properties, the results indicate the dominant role of strain in the magnetic properties of these doped manganites.

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Epitaxial oxide trilayer junctions composed of magnetite (Fe3O4) and doped manganite (La0.7Sr0.3MnO3) exhibit inverse magnetoresistance as large as -25% in fields of 4 kOe. The inverse magnetoresistance confirms the theoretically predicted negative spin polarization of Fe3O4. Transport through the barrier can be understood in terms of hopping transport through localized states that preserve electron spin information. The junction magnetoresistance versus temperature curve exhibits a peak around 60 K that is explained in terms of the paramagnetic to ferrimagnetic transition of the CoCr2O4 barrier.

We have studied the magnetoresistance ͑MR͒ of compressively strained La 0.7 Sr 0.3 MnO 3 ͑LSMO͒ films in various magnetic states in order to understand the role of magnetic domain structure on magnetotransport. In thin films of LSMO on ͑100͒ LaAlO 3 , the perpendicular magnetic anisotropy results in perpendicularly magnetized domains with fine scale ϳ200 nm domain subdivision, which we image directly at room temperature using magnetic force microscopy. The main MR effects can be understood in terms of bulk colossal MR and anisotropic MR. We also find evidence for a small domain wall contribution to the MR, which is an order of magnitude larger than expected from a double exchange model.The doped perovskite manganites have received an enormous amount of attention recently because they exhibit colossal magnetoresistance ͑CMR͒ and may be half metallic, with complete spin polarization at the Fermi level. For these reasons, they may find important uses in magnetoresistive devices, such as magnetic random access memory and sensors. As has been found in magnetoresistive devices based on transition metal ferromagnets, controlling the electronic transport and magnetic properties of these materials in thin film form will be essential to applications. Experimentally, the magnetic and transport properties of colossal magnetoresistance materials have been shown to be highly sensitive to microstructure as well as lattice distortions both in thin film and bulk form. Many groups have shown that properties such as Curie temperature, resistivity and magnetoresistance effect are extremely sensitive to chemical and hydrostatic pressure as well as lattice mismatch with an underlying substrate.1-11 Studies of bulk polycrystalline pellets, thin films of varying polycrystallinity and isolated grain boundaries have shown that the magnetoresistance is profoundly affected by transport across grain boundaries. 2,12,13 Magnetic domain structure may also to lead to distinctive magnetotransport effects in thin films. Mathur et al. report that the measured resistivity of a magnetic domain wall is four orders of magnitude larger than that predicted by a simple double exchange picture.14 Wang et al. have also suggested that large low field magnetoresistance ͑MR͒, in ultrathin compressively strained doped manganite thin films, may be due to domain wall scattering.9 In order to address these questions in LSMO, we have prepared in-plane compressively strained films of LSMO on ͑001͒ LAO (aϭbϭc ϭ3.79 Å) substrates using pulsed laser deposition.9 These films naturally split into stripe domains with length scales set by the strain and film thickness. This enables us to study the effect of magnetic microstructure on MR in a systematic manner. In this letter, we have investigated the magnetics and magnetotransport of epitaxial La 0.7 Sr 0.3 MnO 3 ͑LSMO͒ films. The main MR effects can be explained by CMR and anisotropic MR. We also find evidence for a small domain wall ͑DW͒ contribution to the MR, which is an order of magnitude larger than expected based ...

Low-loss magnetization dynamics and strong magnetoelastic coupling are generally mutually exclusive properties due to opposing dependencies on spin-orbit interactions. So far, the lack of low-damping, magnetostrictive ferrite films has hindered the development of power-efficient magnetoelectric and acoustic spintronic devices. Here, magnetically soft epitaxial spinel NiZnAl-ferrite thin films with an unusually low Gilbert damping parameter (<3 × 10 ), as well as strong magnetoelastic coupling evidenced by a giant strain-induced anisotropy field (≈1 T) and a sizable magnetostriction coefficient (≈10 ppm), are reported. This exceptional combination of low intrinsic damping and substantial magnetostriction arises from the cation chemistry of NiZnAl-ferrite. At the same time, the coherently strained film structure suppresses extrinsic damping, enables soft magnetic behavior, and generates large easy-plane magnetoelastic anisotropy. These findings provide a foundation for a new class of low-loss, magnetoelastic thin film materials that are promising for spin-mechanical devices.

▪ Abstract  Recently there have been significant advances in understanding the magnetic properties of epitaxial ferrite films that are not found in bulk ferrites. Much effort has been expended on trying to achieve bulk properties in thin films for a wide range of applications. From a fundamental science perspective, epitaxial thin films and heterostructures have provided model systems in which novel phenomena, such as modified super-exchange interactions, nearly ideal exchange coupling, and perpendicular exchange coupling, have been observed. These magnetic phenomena and other anomalous magnetic properties are interesting in their own right and are highlighted here.

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