Ruixia Ti

Peculiar magnetism of BiFeO3 nanoparticles with size approaching the period of the spiral spin structure.

Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale.

Magnetic and magnetodielectric properties of Y3−xLaxFe5O12 ceramics

Y3−xLaxFe5O12 (x = 0–0.5) ceramics with garnet structure are prepared by the solid state reaction method and their structural, magnetic, and magnetodielectric properties are investigated systematically. La3+ substitution leads to lattice expansion and possible ion transposition, which oppositely affect the variation of Fe2+ concentration. As a result, both the saturation magnetization and the intrinsic magnetodielectric effect first increase and then decrease with the increase of La concentration. More interestingly, room temperature large magnetodielectric coefficient of about −5% is obtained at 106 Hz and 0.9 T for Y2.7La0.3Fe5O12 ceramics. This study provides a feasible alternative method for modulating the saturation magnetization and the magnetodielectric effect of Y3Fe5O12-based materials.

Nonmonotonic variation of aging behavior in Fe-doped BaTiO3 ceramics

The investigation of ferroelectric aging effect in Fe-doped BaTiO3 ceramics reveals that such effect is first strengthened and then suppressed with the increase content of Fe dopant. Such nonmonotonic variation of aging behavior is considered to be originated from the competition effects between increased concentration of oxygen vacancies and decreased c/a value on the formation of defect dipoles (FeTi′−Vo··)·. This study provides a feasible alternative method for modulating aging effect and will favor the applications of ferroelectrics.

Multiferroic properties and magnetoelectric coupling in Fe/Co co-doped Bi3.25La0.75Ti3O12 ceramics

Polycrystalline Bi3.25La0.75(Ti3−xFex/2Cox/2)O12 (0 ≤ x ≤ 0.5) ceramics are synthesized by the conventional solid state reaction method. Good ferroelectricity and weak ferromagnetism are obtained simultaneously at room temperature when x ≥ 0.2. The ceramics with x = 0.25 possess the best comprehensive properties, including high phase purity, large ferroelectric polarization, great dielectric constant, and also, larger remnant magnetization compared with other samples. Furthermore, significant dielectric anomalies appear near both the ferromagnetic Curie temperature and the spin glass freezing temperature. The possible magnetoelectric coupling mechanism is considered to be the associated binding effect of magnetic interaction on the migration of charged defects, especially oxygen vacancies.

Induction and control of room-temperature ferromagnetism in dilute Fe-doped SrTiO3 ceramics

The magnetic characteristics of dilute Fe-doped SrTiO3 ceramics are studied. The room-temperature ferromagnetism (with transition temperature around 650 K) is successfully realized in Sr0.98Ti0.9Fe0.1O3−δ and Sr0.98Ti0.92Fe0.1O3−δ ceramics. It is found that a fine-tuning of the components could alter the substitution sites of Fe ions and in-turn modulates the magnetism of the material. A systematic analysis reveals that the co-substitution of Fe ions at nonequivalent A and B sites in ABO3 type perovskites is in favor of the ferromagnetism, which could be attributed to the mixed-valence-states of Fe ions and the variation of exchange interactions. This work provides an innovation for the induction and control of ferromagnetism in dilute magnetic materials.

Study of mechanical and dielectric spectrum in YFe1-xMnxO3 ceramics

The mechanical spectra of Mn-substituted yttrium orthoferrite YFe1-xMnxO3 (x = 0, 0.2, 0.3, 0.4) ceramics were performed at kilohertz from 100 to 360 K. Two internal friction (IF) peaks are observed around 150 K and 230 K, respectively, and both the IF peaks exhibit frequency dispersion behavior. The IF peak around 150 K is associated with a step increase in the modulus and its mechanical relaxation rate follows the Vogel-Fulcher relation with τ0 = 4.45 × 10−11s, Eα = 0.03 eV, and TVF = 155 K. This IF peak can be explained in terms of a freezing of oxygen vacancies after excluding the possible magnetic spin glass transition. Another IF peak around 230 K presents a relaxation behavior and it follows Arrhenius law. Furthermore, the relaxation behavior was verified by the dielectric spectrum and it can be ascribed to the charge carrier hopping between Fe2+ and Fe3+.

Combination of conductive filaments and Schottky behavior in multifunctional Sn1−xCuxO2−δ memristor

Resistive switching behaviors of SnO2 films are largely improved by Cu acceptor doping. At a suitable Cu2+ concentration, a high ON/OFF resistance ratio (104), good endurance (104) and long retention (104 s) are achieved in the Cu/SnO2:Cu/Pt sandwich structure with the modulation of carriers and oxygen vacancies. As a memristor, the resistive switching can be triggered by one pulse or a train of pulses, and the latter mode could simulate the long-term potentiation of biological synapses. Moreover, the multi-resistance states during the reset process demonstrate a combination of abrupt and incremental resistive switching. The peculiar conductive behavior of the devices is considered to result from the cooperation of conductive filaments and Schottky barrier, with the oxygen vacancies serving as the bridge. These studies are significant for higher density storage and cognitive computing in future.

Dipole glass behavior of Fe-doped SrTiO3 ceramics

The effects of Fe ions incorporation into the Sr and Ti sites of SrTiO3 ceramics on the dielectric properties are studied in this work. It is found that the dielectric properties of the samples are sensitive to the components. Compared to SrTi0.9Fe0.1O3−δ with paraelectric property, Sr0.98Ti0.9Fe0.1O3−δ and Sr0.98Ti0.92Fe0.1O3−δ present dielectric relaxations at low temperature. After carefully analyzing the dielectric spectra by Arrhenius law and Power law, the dielectric relaxations are mainly attributed to the relaxation polarizations of defect dipoles formed by the off-center Fe ions at the Sr-sites and oxygen vacancies, and the dipole glass behavior are identified at low temperature.