A granular system composed of ferrimagnetic NiFe2O4 nanoparticles, about 8 nm in size, embedded in an antiferromagnetic NiO matrix has been synthesized by a high-temperature phase precipitation method from Fe-doped NiO matrix. Both the exchange bias field and vertical magnetization shift can be observed in this system below 250 K after field cooling, above which the exchange bias disappears. Furthermore, the exchange bias field shows a linear dependence on the magnetization shift. This observed exchange bias effect is explained in terms of the exchange interaction between the ferrimagnetic phase and the spin-glass-like phase at the interface.

Structural, magnetic, and ferroelectric properties have been investigated for Bi2Fe4(1−x)Ti4xO9 (0≤x≤0.2) bulk ceramics, which were synthesized by a modified Pechini method. X-ray diffraction reveals that all samples are single phase with no impurities detected. Compared with antiferromagnetic Bi2Fe4O9 compound, doping with Ti ions induces the appearance of weak ferromagnetism at room temperature, which is discussed in terms of the collapse of the frustrated antiferromagnetic spin structure. Moreover, appropriate Ti doping also significantly reduces electric leakage and leads to the enhancement of electrical polarization. Among all samples, the optimal multiferroics with Mr∼0.0188 emu/g and Pr∼0.262 μC/cm2 at room temperature is found for x=0.15 ceramics. It is thus shown that Ti-doped Bi2Fe4O9 is a promising candidate for preparing multiferroic materials.

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Discrete and uniform microporousCoO nanoparticles with open nanochannels around 1 nm were one-pot synthesized by the self gas-leaching method via the thermal decomposition of a Co-oleylamine complex.CoO particle-sizes can be tuned from 50 to 13 nm by controlling the concentration of the cobalt precursor, accompanying a change of the long and winding nanochannels to short and straight nanochannels. It was shown that exposing the particle interiors to external active reactants via the shorter and straighter microporous nanochannels in smaller CoO nanoparticles can greatly enhance their photocatalytic efficiency. Most importantly, all the as-synthesized microporous CoO nanoparticles showed a very highly reversible capacity and cycling stability for lithium storage. The discharge and charge capacities of the microporous CoO sample with short straight nanochannels and the smallest particle size (1432.8 and 1200 mA h g À1 , respectively) are up to two times higher than those of the commercial CoO powder (673.7 and 539 mA h g À1 , respectively) and that of the theoretical value of CoO (715 mA h g À1 ) owing to the enlarged surface area, very small particle size for increased electrode and electrolyte contact and the heightened diffusion efficiency in short nanochannels for electrolyte and Li ions. The presence of microporous voids could effectively buffer the stress induced during lithium insertion-deinsertion alleviating the pulverization of electrode material, thereby giving extraordinary cycling stability.

Spin-glasslike (SGL) behavior and exchange bias (EB) effect have been reported in multiferroic Bi1/3Sr2/3FeO3 ceramics. Temperature dependence of magnetization and high field relaxation properties reveal the existence of SGL phases. After field cooling the sample from 350 to 10 K, exchange bias field (HEB), vertical magnetization shifts (MShift) and increment of saturation magnetization (MS) are observed, and exhibit a strong dependence on the strength of cooling fields. Furthermore, HEB shows a linear dependence on MShift. This observed EB effect is discussed in terms of the exchange coupling between ferromagnetic clusters and the SGL phases at interface.