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Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co2+/Ni2+ turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu2+/Eu3+, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu–O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states. [ABSTRACT FROM AUTHOR]

Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on the Si and LaNiO3 (LNO) buffered Si substrates at 700 °C, by co-sputtering from two individual targets of the components. The films grown on LNO/Si had a microstructure characterised by fine NZFO grains (∼25 nm) embedded in large BFO grains (＞100 nm), i.e. a typical 0–3 connectivity. A grain–epitaxy relation was observed between BFO and LNO, which were deposited on Si as the bottom electrode. There were residual strains in both BFO and NZFO grains. The former was confirmed by the shift of the d-spacing in X-ray diffraction patterns, while the latter was supported by a uniaxial distortion of the cubic magnetocrystalline anisotropy as revealed by the fitting of the temperature-dependent coercivity. The NZFO + BFO composite films exhibited a clear exchange bias, which was about 37 Oe at 2 K and dropped to 11 Oe at room temperature. The absence of interfacial reaction, as evident by the occurrence of exchange bias, and yet the presence of residual strains from the growth process led to very large magnetoelectric coefficients either with or without a static bias magnetic field. The maximum value reached 869 mV cm−1 Oe−1 at a resonance frequency of 10 kHz and a bias field of 6.5 kOe. [ABSTRACT FROM AUTHOR]