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Ni–Zn ferrite and Bi2O3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction (XRD) was performed to study the crystal structure. The results of field emission scanning electron microscopy (FE-SEM) showed that the addition of Bi2O3 can increase the grain size of the Ni–Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi2O3 ratio. In addition, the dielectric properties of the Ni–Zn ferrite were also improved with the addition of Bi2O3. [ABSTRACT FROM AUTHOR]

We studied the ferromagnetism of Ni-doped SnO2 with and without oxygen vacancy (VO) by experiments and calculations. Sn0.96Ni0.04O2 nanocrystalline powder prepared by the sol-gel method exhibits room-temperature ferromagnetism, and the vacuum annealing reduces its saturation magnetizations. The density functional theory (DFT) calculations show that the doped Ni atom can introduce a local magnetic moment of about 2.0 μB in SnO2 (110) surface, which is ascribed to the spin-polarization of Ni 3d and O 2p electrons. The type of preferential magnetic coupling of Ni-doped SnO2 (110) surface depends upon the distributions of Ni dopants, and ferromagnetic coupling is more favorable in most cases. Introduction of VO obviously weakens the ferromagnetic interaction of Ni-doped SnO2 (110) surface, which can give a reasonable explanation for our experimental observations. [ABSTRACT FROM AUTHOR]

Mn1−xZnxFe2O4 (x = 0.2-0.8) ferrite samples were successfully prepared by the sol-gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn1−xZnxFe2O4 samples. The SEM micrographs revealed that the microstructures change significantly with different Zn2+ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn0.6Zn0.4Fe2O4 sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn2+ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn0.6Zn0.4Fe2O4 sample sintered at 1100 °C for 8 h is found to show the largest Ms value (77.30 emu/g) in this work. These results indicate that Zn2+ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn1−xZnxFe2O4 ferrites. [ABSTRACT FROM AUTHOR]

(Li1+, Zn2+ and La3+) co-substituted NiFe 2 O 4 ferrite ceramics (Ni 0.8-x Zn x Li 0.1 La 0.1 Fe 2 O 4 , x = 0.0, 0.2, 0.4, 0.6, 0.8) were prepared by the sol-gel auto-combustion method. The structural properties were investigated by X-ray diffraction and field emission scanning electronic microscope techniques. Vibrating sample magnetometer and LCR meter were used to probe magnetic and dielectric properties. A relatively high value of saturation magnetization (105.94 emu/g) can be achieved in Ni 0.4 Zn 0.4 Li 0.1 La 0.1 Fe 2 O 4 sample sintered at 1100 °C. In addition, the soft magnetic properties are also enhanced due to a reduced coercivity value. Also, dielectric behavior is improved and all the results show that co-substitution with Li1+, Zn2+ and La3+ ions as well as modulation via Zn2+ ions has a great impact on the properties of Ni ferrites. [ABSTRACT FROM AUTHOR]

• Treatment in O atmosphere at room temperature increase the ferromagnetism. • O 2 molecule can be exothermically adsorbed on the defective ZnO (1 0 0) surface. • Adsorbed O 2 molecule enhances the magnetism of oxygen-deficient ZnO surface. The saturation magnetization of the ZnO nanocrystalline powder prepared by sol-gel method was increased by vacuum annealing, and it can be enhanced again by the further treatment in the oxygen atmosphere at room temperature. The calculations based on density functional theory showed that the O 2 molecule is easy to form the chemical adsorption on the oxygen-deficient surface, and the synergy of the oxygen vacancy and adsorbed O 2 can increase the magnetism. [ABSTRACT FROM AUTHOR]

Abstract Mg x Co 1-x Fe 2 O 4 ferrites were prepared by the sol-gel method and sintered from 1100 °C to 1300 °C. The microstructures, magnetic and dielectric properties have been investigated. XRD patterns demonstrated that the samples have a single spinel phase with cubic symmetry. Mg2+ doping expands the lattice parameter slightly. The grain size increases with increasing sintering temperature but decreases with Mg2+ doping. The saturation magnetization value decreases from 64.26 emu/g to 26.05 emu/g with the increasing Mg2+ concentration from x = 0.2 to x = 1.0. And the coercivity of the samples also decreases from 0.32 kOe to 0.15 kOe. The dielectric results showed that the behavior of dispersion appeared at the low frequency, which can be attributed to the space charge polarization. And the dielectric constant increases with the increasing grain size. All the results indicated that the Mg2+ doping has a significant influence on the properties of CoFe 2 O 4. Highlights • Grain size decreases as the Mg2+ concentration increases from x = 0.2 to x = 1.0. • Ms value decreases rapidly when Mg2+ doping changed from x = 0.4 to x = 0.6. • Saturation field drop down to 0.75 kOe when Mg2+ doping changed from x = 0.2 to x = 1.0. • Only one arc existed in Z ' - Z ″ plot due to co-effect of grain and grain boundary. [ABSTRACT FROM AUTHOR]

Cu x Ni 1−x Fe 2 O 4 powders were prepared by the sol-gel method and the corresponding temperature dependence of microstructure, magnetic and dielectric properties of different Cu x Ni 1−x Fe 2 O 4 samples have been investigated. Results of XRD and SEM indicate that the Cu 2+ concentration played an important role in both crystal phase and particle distribution of Cu x Ni 1−x Fe 2 O 4 . The measurement of magnetic properties shows that both Cu 2+ doping and sintering temperature could change the saturation magnetization and remanent magnetization in a noticeable manner, and even the magnetic material type. The Cu 0.2 Ni 0.8 Fe 2 O 4 sample sintered at 900 °C had the largest saturation magnetization (34.61 emu/g), remanent magnetization (17.85 emu/g) and the lowest coercivity (0.17 kOe). The dielectric measurements show strong frequency dependence for all the samples. The peak observed in frequency dependence of dielectric loss measurements shifts to higher frequency with the increasing Cu 2+ concentration and sintering temperature, indicating a Debye-like dielectric relaxation. All the results indicate that the Cu 2+ doping has a significant influence on NiFe 2 O 4 ferrites. [ABSTRACT FROM AUTHOR]

Cobalt ferrite powders were successfully synthesized by sol-gel auto-combustion method. Influence of sintering temperature on structural, magnetic and dielectric properties was studied. All the obtained samples are spinel ferrite with a cubic symmetry. As the sintering temperature increased from 900 °C to 1300 °C, the average grain size increased from 0.26 μm to 0.83 μm. The dielectric constant and loss tangent measurement showed strong temperature dependence at all frequencies. The maximum magnetization increased while the coercivity and remanent magnetization decreased with the increasing sintering temperature. The non-saturation at high fields may be related to the surface effects in CoFe 2 O 4 samples. When sintered at 1300 °C, the sample showed a maximum magnetization value of ∼87.32 emu/g at room temperature. The highest value of coercivity of all the samples was 1368.33 Oe for the sample sintered at 900 °C. [ABSTRACT FROM AUTHOR]

The emergence of ferromagnetism in perovskite oxide LaFeO 3 nanoparticles and colossal dielectric response in ceramics has inspired researchers to study the effect of various dopants on the magnetic and dielectric properties of LaFeO 3 powders and ceramics. However, the influence of alkali element Na doping has not been studied yet, and the origin of such ferromagnetic behavior is still ambiguous. The primary objective of the present work is to elucidate the effect of Na doping on the magnetic properties of La 1−x Na x FeO 3 (x=0, 0.1 and 0.2) powders and dielectric properties of corresponding ceramics prepared by citric sol-gel method. FE-SEM results showed that the introduction of Na dopant actually resulted in the formation of nonstoichiometric La 1−x FeO 3 and x/2 Na 2 O. Compared to the canted AFM behavior for the pure powder, ferromagnetic behavior with enhanced magnetization of 2.11 emu/g at 10 kOe could be obviously observed at room temperature for the powder with x=0.2. XPS measurement suggested nonstoichiometric Fe/La ratio which leads to the distortion of lattice structure and enlarged canting angle between the two AFM coupled Fe sublattice should be responsible for the enhancement of magnetization in the Na-doped samples. Meanwhile, the introduction of Na dopant lowered the growth temperature of grains of the parent LFO and resulted in larger average grain size, which in turn leaded to great enhancement of ε′ into the order of 10 5 at 100 Hz at the cost of high tanδ for the Na-doped ceramics. [ABSTRACT FROM AUTHOR]

• V O 2+ nearest to the Mn(II) Ti ion is more likely to be formed. • The presence of V O + increases the magnetic moment of the doping system. • The doping system with V O 2+ is more inclined to ferromagnetic coupling. • The introduction of V O 2+ dose not change the magnetic moment of the doping system. We studied the magnetism of Mn(II)-doped anatase TiO 2 (a -TiO 2) with and without oxygen vacancy (V O) by Heyd-Scuseria-Ernzerhof hybrid functional method. Introduction of Mn(II) dopants causes the nonmagnetic a -TiO 2 to have a magnetic moment, which is in direct proportion to the limited doped concentrations. The type of preferential magnetic coupling in Ti 1-δ Mn(II) δ O 2 depends upon the Mn-Mn distance. Introduction of V O + increases the local magnetic moment in Ti 1-δ Mn(II) δ O 2 , and the antiferromagnetism of the system is further enhanced. In contrast, the local magnetic moment of Ti 1-δ Mn(II) δ O 2 with V O 2+ does not change, but the ferromagnetic coupling becomes more stable. [ABSTRACT FROM AUTHOR]