Jiangtao Wu

Room-temperature ferromagnetic/ferroelectric BiFeO3 synthesized by a self-catalyzed fast reaction process

Bismuth ferrite BiFeO3 has attracted a great deal of interest because of its multiferroic properties. However, BiFeO3 synthesized by conventional methods in the forms of single crystals, ceramics or thin films only exhibit ferroelectricity and antiferromagnetic order at room temperature, with weak ferromagnetism appearing at very low temperatures. To fully explore the potential of multiferroism in such applications as new memory devices, it is necessary to synthesize materials that show ferromagnetic order at room temperature as well, which will a priori allow for magnetoelectric coupling. In this paper, we report a new synthetic technique for the synthesis of BiFeO3 that exhibits unusual ferromagnetic properties. This method involves a low temperature fast solid state reaction based on tartaric acid. The mechanism of the reaction deduced from thermogravimetric analysis (TGA) and differential thermal analysis (TGA) suggests that a self-catalyzed process in the presence of iron and bismuth oxides triggers the oxidation of tartaric acid at low temperature and gives out a large amount of heat, which, in turn, leads to the formation of BiFeO3. The BiFeO3 synthesized in this way is ferromagnetic. The origin of the unusual ferromagnetism is supposed to be associated with point defects of oxygen vacancies generated during the self-catalyzed extremely fast exothermic reaction, which suppress the spin circular cycloid in BiFeO3. Ferroelectric hysteresis loops are displayed in the BiFeO3 samples. The presence of room temperature ferromagnetic and ferroelectric orders makes BiFeO3 a truly multiferroic material potentially interesting in such applications as magnetoelectric devices.

Synthesis and room temperature four-state memory prototype of Sr3Co2Fe24O41 multiferroics

Multiferroics exhibit both ferroelectricity and ferromagnetism. The combination of ferroelectricity and ferromagnetism in single phase offers the ability to obtain four physical polarization states, i.e., two electric polarization combined with two magnetic polarization states, achieving four-state memory devices. The four-state memory devices can exponentially increase data storage capacity. In this letter, we synthesized single phase Sr3Co2Fe24O41, which exhibits ferroelectricity,ferromagnetism, and magnetoelectric coupling effect at room temperature. The as-prepared Sr3Co2Fe24O41 was used as a four-state memory prototype. The information was written by electric and magnetic fields, and read out by magnetoelectric coefficient (αE ) with the help of a small bias magnetic field.

Partially inverse spinel ZnFe2O4 with high saturation magnetization synthesized via a molten salt route

Materials with high saturationmagnetization (Ms) is greatly demanded in modern soft magnetic applications. In this work, we synthesized partially inverse spinel ZnFe2O4 in micron scale with the highest Ms (Ms = 5.05 μB) among ferrites. What’s more, it exhibits high Curie temperature (640 K), high resistivity, and excellent thermo-stability. Through careful analyses, including Mossbauer spectroscopic, x-ray diffraction, and x-ray photo-electron spectroscopic measurements, it was concluded that the strong ferromagnetism of the as-prepared ZnFe2O4 resulted from its partially inverse spinel structure. These excellent properties indicate the as-prepared ZnFe2O4 is an ideal kind of soft magnet.

Room-Temperature Weak Ferromagnetism Induced by Point Defects in α-Fe2O3

Unusual room-temperature weak ferromagnetism alpha-Fe(2)O(3) was prepared by heating the mixture of commercial alpha-Fe(2)O(3) (as raw material) and tartaric acid at a mild temperature of 250 degrees C. This reaction involves a fast heating and cooling process resulting from the self-catalyzed oxidation of tartaric acid. Careful chemical analyses confirmed that no any ferromagnetic impurities, such as Fe, Fe(3)O(4), amorphous iron oxide and gamma-Fe(2)O(3,) were present in the treated sample. The unusual weak ferromagnetism was then attributed to the formation of a large amount of point defects in the treated sample during the peculiar synthetic process. Such a mechanism is supported by the result of annealing, which reduces the amount of point defects and thereby reestablishes the original antiferromagnetism in alpha-Fe(2)O(3).

Structure and multiferroic properties of Bi(1-x)DyxFe0.90Mg0.05Ti0.05O3 solid solution

Chemical modification is proven to be an effective way to improve the properties of perovskite BiFeO3 (BFO). In this paper, we studied the effects of the A-site Dy3+ ion substitution on the structure and multiferroic properties of BFO in which the Fe3+ ion on the B-site is partially co-substituted for by Mg 2+ and Ti4+ ions. The solid solution compounds of Bi(1-x)DyxFe0.90 Mg 0.05Ti0.05O3 (x = 0 – 1) were synthesized by a tartaric acid-assisted solution process, followed by thermal treatments at 850 °C. The structural transition and the ferroelectric and magnetic properties as a function of composition were investigated. It is found that the structure transforms from a rhombohedral (R3c) to an orthorhombic phase (Pn2 1 a) when x is increased to ≥ 0.15. The ferroelectric measurements indicate that the sample with x = 0.15 possesses the best ferroelectric property, and the remnant polarization of the samples with orthorhombic symmetry decreases with the increase of Dy3+ concentration. The compounds of Bi(1-x)DyxFe0.90 Mg 0.05Ti0.05O3 (x = 0.05 – 1.00) exhibit weakly ferromagnetic properties at low temperatures, but antiferromagnetic behavior at high temperatures. The magnetization of the solid solution increases linearly with the increase of the Dy3+ amount.

Magnetic, recyclable PtyCo1−y/Ti3C2X2 (X = O, F) catalyst: a facile synthesis and enhanced catalytic activity for hydrogen generation from the hydrolysis of ammonia borane

Exploring the applications of two dimensional layered Ti3C2X2 (X = OH, F) is of great importance because of its excellent physical and chemical properties. Herein, we report the synthesis of the bimetallic catalyst PtyCo1−y/Ti3C2X2via a facile one-pot approach using Ti3C2X2 as the support. The in situ synthesized PtyCo1−y/Ti3C2X2 is subsequently applied as a catalyst for hydrogen evolution from the hydrolysis of ammonia borane at 25 °C. Experimental results show that Pt0.08Co0.92/Ti3C2X2 exhibits excellent catalytic activity for the hydrolysis of ammonia borane with a high hydrogen generation rate of 100.7 L H2 (min gPt)−1 and turnover frequency of 727 mol H2 (min molPt)−1 because of the synergistic effect between Pt and Co. Moreover, Pt0.08Co0.92/Ti3C2X2 could be recovered from the reaction mixture by a magnet and recycled at least seven times, thus showing its high recycling efficiency.

Tunable magnetic pole inversion in multiferroic BiFeO3–DyFeO3 solid solution

In ferromagnets, the magnetic moment can generally be reversed by applying a sufficiently high external magnetic field of opposite polarity. Temperature, on the other hand, is usually known to affect only the magnitude of a magnetic moment, rather than its sign or polarity (most magnets exhibit a monotonic increase in magnetization upon cooling below their magnetic phase transition temperature). As a result, temperature-induced magnetization reversal (i.e. magnetic pole inversion) remains a very rare phenomenon which lacks proper understanding and explanation because of the extreme difficulties encountered in controlling the thermodynamics of magnetization of classical metal or metal oxide magnets. Herein, we report an unusual magnetic pole inversion behaviour in multiferroic (1 − x)BiFeO3–xDyFeO3 solid solution (alloy), which can be tuned by varying the concentration of the magnetic ion Dy3+ in the solid solution. It is found that the temperature-induced magnetic pole inversion occurs in a wide composition range (x = 0.14–0.90). Moreover, for the first time in any ferrites, multiple magnetic pole inversions are observed in the solid solution compounds of high Dy3+-concentrations. Our results may provide a better understanding of the temperature- and composition-induced magnetic pole inversion and related phenomena and point to new potential applications for magnetic and multiferroic materials.