Transport properties of aliovalent-ion-doped BiFeO3 (BFO) thin films have been studied in order to identify the cause of high leakage currents. Doping of 2at.% Ti4+ ions increased the dc resistivity by more than three orders of magnitude. In contrast, doping of 2+ ions such as Ni2+ reduced the dc resistivity by two orders of magnitude. Current–voltage (I–V) characteristics indicated that the main conduction mechanism for pure and Ni2+ doped BFO was space charge limited, which was associated with the free-carriers trapped by the oxygen vacancies, whereas in the Ti4+ doped BFO, field-assisted ionic conduction was dominant.

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Low‐leakage BiFeO3 films have been grown with saturated ferroelectric hysteresis loops (see figure) and a very large remanent polarization. The antiferromagnetic nature of BiFeO3 films is confirmed by the appearance of an exchange bias in BiFeO3‐based spin‐valve multilayers. The results imply that there is potential for room‐temperature applications of BiFeO3 that combine ferroelectric and antiferromagnetic functionality.

The magnetic and transport properties of the Cr-doped manganites La(0.46)Sr(0.54)Mn(1-y)Cr(y)O3 ( 0 < or = y < or = 0.08) with the A-type antiferromagnetic structure were investigated. Upon cooling, we find multiple magnetic phase transitions, i.e., paramagnetic, ferromagnetic (FM), antiferromagnetic (AFM), and spin glass in the y = 0.02 sample. The low temperature spin glass state is not a conventional spin glass with randomly oriented magnetic moments but has a reentrant character. The reentrant spin glass behavior accompanied by the anomalous multiple magnetic transitions might be due to the competing interactions between the FM phase and the A-type AFM matrix induced by the random Cr impurity.

We have investigated magnetic microstructures of magnetoresistive La0.7Sr0.3MnO3 (LSMO) thin films. Magnetic images are strongly dependent on structural strain induced by the substrates. The LSMO film on SrTiO3 dominated by tensile stress effect displays a feather-like pattern, whereas LSMO films on LaAlO3 and NdGaO3 substrates under compressive stress show stripe domains. In particular, the magnetic image of the film on NdGaO3 reveals distinctive straight stripe domain patterns on the order of about 120 nm, suggesting the presence of a sizable out-of-plane magnetization. The ordering of the stripe domains is also sensitive to the field direction.

We report magnetic and electronic properties of La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on perovskite substrates by pulsed laser deposition, which are varied with oxygen background pressure and film thickness. The strains of the LSMO films are tuned by the two parameters but their resulting effects are somewhat different. The lattice strain induced by the oxygen pressure suppresses the ferromagnetic transition (TC) and metal–insulator transition (TMI) temperatures. With decreasing film thickness from 110 to 11 nm, however, small changes in both TC and TMI were observed. These results suggest that the physical properties of the LSMO films are strongly dependent on the oxygen content but less sensitive to the film thickness.

High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to study BiFeO3 thin films grown on the bare and SrRuO3 buffered (001) SrTiO3 substrates. Reciprocal space mapping (RSM) around (002) and (103) reflections revealed that BFO films with a thickness of about 200 nm were almost fully relaxed and had a rhombohedral structure. Cross-sectional, high-resolution TEM showed that the films started to relax at a very early stage of growth, which was consistent with the RSM results. A thin intermediate layer of about 2 nm was observed at the interface, which had a smaller lattice than the overgrown film. Twist distortions about the c axis to release the shear strain introduced by the growth of rhombic (001) BiFeO3 on cubic (001) SrTiO3 were also observed. The results indicate that a strained, coherent BiFeO3 film on (001) SrTiO3 is very difficult to maintain and (111) STO substrates are preferable.

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