Perpendicular magnetization and precise control over the magnetic easy axis in magnetic thin film is necessary for a variety of applications, particularly in magnetic recording media. A strong (111) ...orientation is successfully achieved in the CoFe2O4 (CFO) thin film at relatively low substrate temperature of 100 °C, whereas the (311)-preferred randomly oriented CFO is prepared at room temperature by the DC magnetron sputtering technique. The oxygen-deficient porous CFO film after post-annealing gives rise to compressive strain perpendicular to the film surface, which induces large perpendicular coercivity. We observe the coercivity of 11.3 kOe in the 40-nm CFO thin film, which is the highest perpendicular coercivity ever achieved on an amorphous SiO2/Si substrate. The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime. Importantly, this can be achieved on virtually any type of substrate.
This work reports a facile one-step hydrothermal method to synthesize the microsphere SnO2 particles without using any organic agent. The experiment results show that the obtained SnO2 microspheres ...consisting number of nanocrystalline particles of 2–5 nm in size. Oxygen vacancies are also existing on the surface of the SnO2 microspheres. The as-prepared SnO2 microspheres possess mesoporous structure of remarkably high specific surface area (111.27 m2g-1). The gas sensing properties of the as-prepared SnO2 microspheres for ethanol was investigated. The response and recovery time of SnO2 sensor surprisingly reached to 3 s and 24 s respectively under 100 ppm flow of ethanol at an operating working temperature of 230 °C. The response of sensor for 100 ppm of ethanol is enhanced to 24.9 at 230 °C. The excellent ethanol-sensing performance of the fabricated sensor has been attributed to its small grain size, high specific surface area and number of oxygen vacancies of SnO2. These results indicating that the SnO2 microspheres obtained in this work is a promising and excellent ethanol-sensor material.
Conventional refrigeration methods based on compression–expansion cycles of greenhouse gases are environmentally threatening and cannot be miniaturized. Electrocaloric effects driven by electric ...fields are especially well suited for implementation of built-in cooling in portable electronic devices. However, most known electrocaloric materials present poor cooling performances near room temperature, contain toxic substances, and require high electric fields. Here, we show that lead-free ferroelectric thin-film bilayers composed of (Bi0.5Na0.5)TiO3–BaTiO3 (BNBT) and Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 (BCZT) display unprecedentedly large electrocaloric effects of ∼23 K near room temperature under moderate electric bias. The giant electrocaloric effect observed in BNBT/BCZT bilayers, which largely surpasses the sum of the individual caloric responses measured in BNBT and BCZT, is originated from the presence of compositional bound charges at their interface. Our discovery of interface charge-induced giant electrocaloric effects indicates that multilayered oxide heterostructures hold tremendous promise for developing highly efficient and scalable solid-state cooling applications.
•(1-x)BaTiO3/xSr0.92Ca0.04Mg0.04Fe12O19 composites were prepared.•The grains size of BTO phase decreased with increasing SrCaMg hexaferrite content.•The band gap energy (Eg) reduced with the increase ...in x ratio.•Ms, Mr and Hc increased with increasing x ratio.•Dielectric properties depend largely on x content and microstructure of composite.
In the present work, we investigated the correlation between structure, microstructure, optical, electrical, dielectric and magnetic properties in composites based on ferrimagnetic Sr0.92Ca0.04Mg0.04Fe12O19 (noted SrCaMg) and ferroelectric BaTiO3 (noted BTO) phases in different ratio. Series of (1-x)BaTiO3/xSr0.92Ca0.04Mg0.04Fe12O19 mixtures (with x = 0.00, 0.25, 0.50, 0.75 and 1.00) were synthesized. The constituents were selected by taking into consideration the perspective ferroelectric and ferrimagnetic characteristics of BaTiO3 and Sr0.92Ca0.04Mg0.04Fe12O19, respectively. X-ray diffraction (XRD) investigations showed the co-existence of tetragonal BaTiO3 (noted BTO hereafter) and Sr0.92Ca0.04Mg0.04Fe12O19 hexagonal ferrite (noted SrCaMg HF) phases in the produced composites. The phase content of ferrimagnetic SrCaMg HF phase is increasing with increasing x content. The lattice parameter ‘a’ for both BTO and SrCaMg HF phases is almost constant with increasing the x content. However, the lattice parameter ‘c’ is decreasing for BTO phase and increasing for SrCaMg HF phase. The crystallites size (DXRD) is decreasing for BTO phase and increasing in SrCaMg HF phase as the x content increases. The homogeneous distribution of different phases was confirmed via scanning and transmission electron microscopies analyses and the corresponding selected area electron diffraction (SAED) patterns. On increasing the content of SrCaMg hexaferrite phase, the grains size of BTO phase is decreasing. The band gap energy (Eg) values were determined from the analysis of UV–vis diffuse reflectance spectra. BTO nanoparticles (x = 0.00) displays Eg value equal to 3.27 eV. It is found that Eg value is reduced with increasing the concentration of SrCaMg hexaferrite phase reaching values of 3.21, 3.08, 2.91 and 1.23 eV for x = 0.25, 0.50, 0.75 and 1.00, respectively. The saturation magnetization (Ms) and remanence (Mr) were increased with increasing the concentration of SrCaMg HF in the composite. Ms and Mr values are increased from about 0.09 and 0.02 emu/g for x = 0.00 to around 68.8 and 44.7 emu/g for x = 1.00. Compared to x = 0.00 sample, the coercivity (Hc) was increased sharply from 400.5 to 3295 Oe for x = 0.25 and then slightly diminishes with further increasing x. It was noticed that the dielectric properties of various composites depend largely on the x content that alters the microstructure of composite. This was discussed with respect to the microstructure and temperature effect.
Due to its strong redox ability, high stability, cost effectiveness and non-toxicity, cerium oxide (CeO2) has been extensively researched as an active photocatalyst material. The underlying ...photocatalytic reactions are mostly associated with the transportation of oxygen ions through vacancies, but the actual transport phenomenon had not been clearly understood. In this work, gadolinium (Gd) is sequentially doped into CeO2 to investigate how extrinsic doping can modulate oxygen vacancies in CeO2 and influence photocatalytic activities. From our investigations, it was found that the Gd doping may induce structural symmetry breaking leading to a pure CeO2 fluorite structure that transforms mobile oxygen vacancies into clustered or immobile vacancies. When the vacancies were set as "mobile" (for Gd doping levels ≤15 at%), maximum photocatalytic activities were obtained. In contrast, suppressed photocatalytic efficiencies were noted for higher Gd doping levels (20 at% or more). The results reported in this research may provide an extra degree of freedom in the form of extrinsic doping to configure the oxygen vacancy defects and their mobility to achieve better catalytic efficiencies.
Surface amorphization via a crystalline/amorphous core–shell structure is known to be an effective approach to construct a high-efficiency photocatalyst. It enables decreasing of the bandgap of the ...crystalline core and facilitates rapid carrier transmission between the core and shell. However, this kind of structure induces light blocking for the crystalline core that results in fewer photogenerated carriers. In this work, we have fabricated SnO2 microspheres with a novel crystalline/amorphous stacking structure that has a significant effect on photocatalytic NO removal under visible light irradiation. The increase in the NO removal photocatalytic performance is attributed to the increased charge separation efficiency at the crystalline/amorphous interface arising from the built-in electric field between the amorphous and crystalline regions. Moreover, the crystalline/amorphous stacking structure can inhibit surface absorption competition between O2 and NO. Such a process contributes towards the generation of more oxygen active species which could oxidize NO to NO3−. This work demonstrates that the utilization of the crystalline/amorphous stacking structure provides a new strategy to manipulate the charge transport and promote the photocatalytic performance for a high-efficiency photocatalytic material.
The present work is focused on the effect of Fe
3+
replacement by rare earth-Ho
3+
ions and their influence on the properties of MnFe
2
O
4
ferrite. The Ho
3+
substituted MnFe
2
O
4
ferrite samples ...with chemical formula MnHo
x
Fe
2−
x
O
4
were synthesized where substitution concentration of Ho
3+
was 0.0, 0.05, 0.1 and 0.15. The samples were synthesized by the self-ignited sol-gel method using the nitrates of the respective elements. Powder X-ray diffraction, transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometer (VSM) and electrical measurements were employed to characterize the structural, magnetic and electrical properties of these ferrite nanoparticles. The cations distribution between the tetrahedral (A-site) and octahedral sites (B-site) has been estimated by XRD analysis. It is found that substitution of Ho
3+
ions favorably influenced the magnetic and electrical properties. Magnetic measurements were carried out at 77 and 300 K. Saturation magnetization and coercivity increased from 54.57 to 71.6 emu g
−1
and 172 to 766 Oe, respectively, with increasing the Ho
3+
substitution. The change in magnetic properties may be explained with the increase of A-O-B (Fe
A
3+
-O
2−
-Ho
B
3+
) super exchange interactions and the anisotropy constant. The electrical properties show that the pure sample has lower resistivity with respect to any Ho
3+
doped one. The conduction mechanism is used to interpret electrical measurements. Results of the presently investigated samples with enhanced saturation magnetization, coercivity and remanence ratio indicate that the Ho
3+
doped MnFe
2
O
4
nanoparticles can be a useful candidate for the application in high density recording media.
The occurrence of 4f-3d couplings in MnHo
x
Fe
2−
x
O
4
determines the magnetocrystalline anisotropy in ferrites and improves their magnetic properties.
•CoCexDyxFe2-2xO4 were synthesized through citrate-gel combustion method.•XRD results confirm the formation of spinel cubic structure of the ferrites.•Ferrite sample with x = 0.03 show high ...dielectric constant and low dielectric loss.•Impedance analysis confirms that the conduction is due to the grain boundary.•Ferrite with x = 0.03 is desirable for the use in high frequency electromagnetic devices.•Magnetization values decreased and coercivity increased with increase in Ce and Dy.
Ce and Dy substituted Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz–10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased.
•Single-phase CoEuxFe2−xO4 (0.00 ≤ x ≤ 0.10) nanosized spinel ferrites were synthesized via sonochemcial approach.•Optical band gap energy (Eg) values are in a narrow band of ...1.34 eV–1.44 eV.•Magnetic properties revealed superparamagnetic property at room temperature and soft ferrimagnetic nature at 10 K.•Eu3+ substitutions significantly affect the magnetizations data of Co nanosized ferrites.•A decreasing trend in the Ms, Mr and nB values was noted with Eu3+ substitutions.
Nanoparticles (NPs) of composition Co0.3Ni0.5Mn0.2EuxFe2−xO4, where 0.00 ≤ x ≤ 0.10 (hereafter called CNMEuF) were synthesized by sonochemical approach using UZ SONOPULS HD 2070 ultrasonic homogenizer (frequency of 20 kHz and power of 70 W). As-synthesized samples were characterized thoroughly to determine the effects of europium ions (Eu3+) substitution on their structure, morphology and magnetic traits. Structural analyses of the synthesized NPs confirmed their high purity and crystalline cubic phases. Percent diffuse reflectance (%DR) data and Kubelka-Munk theory were exploited to evaluate the optical band gap energies of the studied CNMEuF NPs. Values of optical band gap energies obtained from the Tauc plots were observed in the range of 1.47–1.58 eV. The hysteresis loops (at room temperature and 10 K) of synthesized NPs were analyzed to determine their magnetic properties. These NPs disclosed superparamagnetic and hard ferrimagnetic character at room temperature and 10 K, respectively. With exception, the sample with x = 0.10 revealed soft ferrimagnetic behavior at 10 K. Eu3+ doping was shown to have significant influence on the structure and magnetic attributes of the proposed CNMEuF NPs. Values of various magnetic parameters of proposed compositions were reduced with the increase in Eu3+ dopant contents.
Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li0.5Fe2.5O4) were synthesized and sintered at four different temperatures ranging from 875 to ...1475K in the step of 200K. The sample sintered at 875K was also treated for four different sintering times ranging from 4 to 16h. Samples sintered at 1475K have the cubic spinel structure with a small amount of α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite). The samples sintered at≤1275K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13–45nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76emu/g and coercivity decreases from 151 to 139Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100Oe. Typical blocking effects are observed below about 244K. The dielectric constant increases with an increase in sintering temperature and particle size.
► Lithium ferrite with heat treatment. ► Structure changes from disordered system to ordered system. ► Magnetization increases with sintering temperature. ► Blocking temperature increases with sintering temperature. ► Coercivity decreases with sintering temperature.
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