Enhancement of Interparticle Exchange Coupling in CoFe2O4/CoFe2 Composite Nanoceramics Via Spark Plasma Sintering Technology

Powders and nanoceramics composed of composites of CoFe₂O₄, CoFe₂, and a small amount of FeO were prepared by heating CoFe₂O₄ powder in reducing atmosphere and by sintering the product of reducing reaction at 350°C via spark plasma sintering technology. In the powders, increase in the molar ratios of CoFe₂:CoFe₂O₄ and a great change in magnetic parameters were observed with the change in heating temperature from 300°C to 400°C, and the dominance of dipole interaction over exchange coupling in the interparticle interactions was confirmed by the steps in magnetic hysteresis loops and the negative Henkel plots. However, in the nanoceramics, significant enhancement in exchange coupling was found when the sintering temperature was raised to 500°C and 650°C, which was confirmed by both the positivity of Henkel plot and the single‐phase style of the magnetic hysteresis loop.     

Improved magnetic and electromagnetic absorption properties of xSrFe12O19/(1−x)NiFe2O4 composites

xSrFe₁₂O₁₉/(1−x)NiFe₂O₄ composites (0 ≤ x ≤ 1.0) were synthesized by using a conventional solid-state synthetic route. The results show that magnetic hysteresis loops of the xSrFe₁₂O₁₉/(1−x)NiFe₂O₄ composites are similar to those of individual component ferrites, except for the 0.1SrFe₁₂O₁₉/0.9NiFe₂O₄ and 0.3SrFe₁₂O₁₉/0.7NiFe₂O₄, suggesting that the hard/soft magnetic phases are well exchange-coupled. The saturation magnetization, coercivity, and remanent magnetization of the xSrFe₁₂O₁₉/(1−x)NiFe₂O₄ composites are increased with increasing content of SrFe₁₂O₁₉, with maximal values of 42.1 Am² kg⁻¹, 78.7 kA m⁻¹, 17.2 Am² kg⁻¹, respectively, as the content x is about 0.5. They are higher than those of the individual components, implying that interface coupling is present in the magnetic composites. The coercivity and remanent magnetization of the composites are increased initially with increasing sintering temperature and then show a downward tendency. For the component SrFe₁₂O₁₉ and NiFe₂O₄, the minimum reflection losses are −12.5 dB and −18.3 dB at match thicknesses of 2.5 mm and 2 mm, respectively. Compared with those of the component SrFe₁₂O₁₉ and NiFe₂O₄, the microwave absorption performances of the xSrFe₁₂O₁₉/(1−x)NiFe₂O₄ composites are improved remarkably, especially for the samples of x = 0.3 and x = 0.9. The minimum reflection losses values of the 0.3SrFe₁₂O₁₉/0.7NiFe₂O₄ composite are −31.6 dB (12.7 GHz) and −20.2 dB (13 GHz), while those of the 0.9SrFe₁₂O₁₉/0.1NiFe₂O₄ composites are −23.7 dB (16.3 GHz) and −33.5 dB (15.8 GHz), as the matching thicknesses are 2.5 mm and 2 mm, respectively. Therefore, the xSrFe₁₂O₁₉/(1−x)NiFe₂O₄ composites could be used as potential microwave absorption materials.     

Spark Plasma Sintered HA‐Fe3O4‐Based Multifunctional Magnetic Biocomposites

Although HA is highly biocompatible, one of the major disadvantages of HA include the lack of antibacterial property. In an earlier study, we demonstrated the potential role of magnetic field stimulation on bactericidal property in vitro. Following this, it was hypothesized that antibacterial property can be realized if bacteria are grown on magnetic biocomposites in vitro. In addressing this issue, this study demonstrates the development of HA‐Fe₃O₄‐based magnetic substrate with multifunctional properties. For this purpose, HA‐xFe₃O₄ (x: 10, 20 and 40 wt%) powder compositions were sintered using uniquely designed spark plasma sintering conditions (three stage sintering with final holding temperature of 1050°C for 5 min). A saturation magnetization of 24 emu/g is measured with HA‐40%Fe₃O₄. Importantly, all the HA‐Fe₃O₄ composites demonstrated bactericidal property by rupturing the membrane of Escherichia coli bacteria, while supporting cell growth of metabolically active human fetal osteoblast cells over 8 d culture. A systematic decrease in bacterial viability with Fe₃O₄ addition is consistent with a commensurate increase in reactive oxygen species (ROS).     

Synthesis,characterization, and magneto‐electric properties of (1−x)BCZT‐xCFO ceramic particulate composites

Synthesis of a new magnetoelectric [(1?x)(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃‐xCoFe₂O₄] (weight fraction x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1) ceramic particulate composites with its structural characterization and magneto‐electric properties have been reported here in this study. Lead free piezoelectric (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) and ferrimagnetic CoFe₂O₄ (CFO) were synthesized using sol‐gel and combustion methods respectively. (1?x)BCZT‐xCFO magnetoelectric composites were then synthesized by mixing of the calcined individual ferroic phases with required weight fractions. Powder X‐ray diffraction studies indicate the coexistence of BCZT and CFO phases in the composites sintered at 1300°C. 0.5BCZT‐0.5CFO composite showed high strain sensitivity (dλ/dH) of 52×10^?9 Oe^?1, which is comparable to that of pure CFO (50×10^?9 Oe^?1). A high piezoelectric voltage constant (g₃₃) of 8×10^?3 V m/N was measured for 0.8BCZT‐0.2CFO sample. All the composites showed magnetoelectric effect and a high magnetoelectric coupling coefficient (α_ME) of 6.85 mV/cm Oe was measured for 0.5BCZT‐0.5CFO composite at 1 kHz and a large ME coefficient of 115 mV/cm Oe at its resonance frequency. The effect of microstructure on the magnetoelectric properties of [(1?x)BCZT‐(x)CFO] composites has been studied and reported here as a function of its piezoelectric (BCZT)/ferrite (CoFe₂O₄) content.     

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Neodymium silicate apatites are promising intermediate temperature (500°C–700°C) electrolytes for solid oxide fuel cells. The introduction of Al promotes isotropic percolation of O^2?, and at low levels (0.83–2.0 wt% Al) enhances bulk conductivity. To better understand the effect of Al‐doping on intrinsic conductivity, and the impact of grain boundaries on the transport, dense Nd_9.33+x/3Al_xSi_6?xO₂₆ (0 ≤ x ≤ 2) pellets were prepared by spark plasma sintering. Phase purity of the products was established by powder X‐ray diffraction and the microstructure examined by scanning electron microscopy. The ionic conductivity measured by AC impedance spectroscopy for the spark plasma sintered ceramics were compared with transport in single crystals of similar composition. Intermediate Al‐doping (0.5 ≤ x ≤ 1.5) delivered superior overall conductivity for both the polycrystalline and single crystal specimens.     

Creep behaviour of alumina/YAG composites prepared by different sintering routes

Al₂O₃-5 vol.% Y₃Al₅O₁₂ (YAG) composite powders have been prepared by surface doping of α-alumina powders by an yttrium chloride aqueous solution. Two commercial, one submicron-sized, the other ultra-fine, alumina powders were compared as matrix materials. YAG phase was yielded by an in situ reaction promoted by the subsequent thermal treatment of the doped powders. In particular, a flash soaking into a tubular furnace kept at a fixed temperature in the range 1050-1150 °C was employed, for inducing the crystallization of yttrium-aluminates on the alumina particles surface, but avoiding a relevant crystallites growth. After that, aqueous suspensions of the calcined powders were dispersed by ball-milling and cast into porous moulds or simply dried in a oven. Slip cast green bodies were densified by pressure-less sintering, while powdered samples were consolidated by hot pressing or spark plasma sintering. The low- and high-temperature mechanical performances of the sintered materials were investigated and related to monolithic aluminas behaviour as well as to the composites microstructures. It is shown that the hot-pressed and spark plasma sintered composites present a significantly lower creep rate as compared to reference, monolithic alumina samples.     

Study of strontium ferrites substituted by lanthanum on the structural and magnetic properties

M-type strontium ferrites, Sr_0.8La_0.2Fe₁₂O₁₉ have been synthesized by conventional ceramic process. The effects of lanthanum addition and sintering temperature on microstructures and magnetic properties of SrFe₁₂O₁₉ and Sr_0.8La_0.2Fe₁₂O₁₉ samples were investigated. Microstructural analysis of the SrFe₁₂O₁₉ and Sr_0.8La_0.2Fe₁₂O₁₉ specimens, sintered at different temperatures revealed that average grain sizes of SrFe₁₂O₁₉ ferrites were larger than that of Sr_0.8La_0.2Fe₁₂O₁₉ ferrite and increased with increasing sintering temperature. The X-ray diffraction (XRD) results confirmed the strontium hexagonal ferrite phase of SrFe₁₂O₁₉ and Sr_0.8La_0.2Fe₁₂O₁₉ compounds. A maximum coercivity value of 4850 Oe and maximum saturation magnetization value of 102 emu/g were obtained for the SrFe₁₂O₁₉ ferrite sintered at 1150 °C and for the SrFe₁₂O₁₉ and Sr_0.8La_0.2Fe₁₂O₁₉ ferrites sintered at 1300 °C, respectively. The remanence (Mr) of Sr_0.8La_0.2Fe₁₂O₁₉ sample sintered at 1200 °C possesses the maximum value of 60 emu/g.     

Preparation and electromagnetic properties of the BaFe12O19/multiwall carbon nanotubes/poly(3‐methyl‐thiophene) composites

The BaFe₁₂O₁₉/multiwall carbon nanotubes/poly(3‐methyl‐thiophene) (BaFe₁₂O₁₉/MCNTs/P(3MT)) composites were synthesized through an in situ chemical polymerization of 3‐methyl‐thiophene (3MT) in the presence of BaFe₁₂O₁₉/MCNTs composite powders. The BaFe₁₂O₁₉/MCNTs/P(3MT) composites were characterized by the fourier transform infrared spectrometry (FTIR) and X‐ray diffraction (XRD). The morphologies of the composites were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electric conductive properties were tested by a four‐probe conductivity tester and the magnetic properties were measured by vibrating sample magnetometer (VSM). The electromagnetic performance tests showed that when the mass ratio of BaFe₁₂O₁₉ to MCNTs was 0.4, and the BaFe₁₂O₁₉/MCNTs to P(3MT) was 0.15, the conductivity, saturation magnetization (M_s) and residual magnetization (M_r) of the BaFe₁₂O₁₉/MCNTs/P(3MT) composites achieved 166.740 S/m, 29.884 emu/g, and 17.581 emu/g, respectively. POLYM. COMPOS., 34:1801–1808, 2013. © 2013 Society of Plastics Engineers     

Low‐Temperature Sintering of HfC/SiC Nanocomposites Using HfSi2‐C Additives

HfC/SiC nanocomposites were fabricated via the reactive spark plasma sintering (R‐SPS) of a nano‐HfC powder and HfSi₂‐C sintering additives. The densification temperature decreased to 1750°C as the additive content increased. XRD analysis indicated the formation of pure HfC–(19.3–33.8 vol%) SiC within the sintered composites without residual silicide or oxide phases or secondary nonoxide phases. Ultrafine and homogeneously distributed HfC (470 nm) and SiC (300 nm) grains were obtained in the dense composites using nano‐HfC powder through the high‐energy ball‐milling of the raw powders and R‐SPS. Grain growth was further suppressed by the low‐temperature sintering using R‐SPS. No amorphous phase was identified at the grain boundary. The maximum Vickers hardness, Young's modulus, and fracture toughness values of the HfC/SiC nanocomposites were 22 GPa, 292 GPa, and 2.44 MPa·m^1/2, respectively.     

Effect of sintering temperature on the structural and magnetic properties of MgFe2O4 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) is a powerful technique to produce fine grain dense ferrite at low temperature. This work was undertaken to study the effect of sintering temperature on the densification, microstructures and magnetic properties of magnesium ferrite (MgFe₂O₄). MgFe₂O₄ nanoparticles were synthesized via sol–gel self-combustion method. The powders were pressed into pellets which were sintered by spark plasma sintering at 700–900 °C for 5 min under 40 MPa. A densification of 95% of the theoretical density of Mg ferrite was achieved in the spark plasma sintered (SPSed) ceramics. The density, grain size and saturation magnetization of SPSed ceramics were found to increase with an increase in sintering temperature. Infrared (IR) spectra exhibit two important vibration bands of tetrahedral and octahedral metal-oxygen sites. The investigations of microstructures and magnetic properties reveal that the unique sintering mechanism in the SPS process is responsible for the enhancement of magnetic properties of SPSed compacts.     

Influence of Ln3+ and B3+ Ions Co‐Substitution on Thermophysical Properties of LnMB11O19‐type Magnetoplumbite LaMgAl11O19 for Advanced Thermal Barrier Coatings

Lanthanum hexaaluminate is a promising competitor to establish yttria partially stabilized zirconia as a thermal barrier coating material for Ni‐based superalloy due to its relative low intrinsic thermal conductivity and low sinterability at temperatures exceeding 1100°C. Sr²⁺ and Ti⁴⁺ were selected as two dopants to partially substitute the La³⁺ and Al³⁺ in LaMgAl₁₁O₁₉, respectively. The variation in thermal conductivity with Sr²⁺ and Ti⁴⁺ fractions was analyzed based on structure information provided by X‐ray diffraction and Raman spectroscopy. The average crystal size of LaMgAl₁₁O₁₉ sintered at 1600°C for 10 min by spark plasma sintering is in nanoscale. The fully dense La_1?xSr_xMgAl_11?xTi_xO₁₉ solid solution showed a minimum thermal conductivity value (λ = 1.12 W/(m K)^?1,T = 1273 K) at the composition of La_0.5Sr_0.5MgAl_10.5Ti_0.5O₁₉,which possibly reduces from the enhanced phonon scattering due to mass and strain fluctuations at the Ln³⁺ and B³⁺ sites.     

Characterisation of plasma-sprayed SrFe12O19 coatings for electromagnetic wave absorption

SrFe₁₂O₁₉ coatings, intended as electromagnetic wave absorbers, were produced by atmospheric plasma spraying (APS) using two different kinds of feedstock powders: spray-dried agglomerates of micrometric SrFe₁₂O₁₉ particles (type-A) or spray-dried agglomerates of raw materials (SrCO₃, Fe₂O₃), reactively sintered at 1100 °C (type-B).During spraying, type-A agglomerates either remain unmelted, producing porous coating regions where crystalline hexaferrite is retained, or are disrupted into smaller granules which melt completely, resulting in dense coating regions with no crystalline hexaferrite.The sintered type-B agglomerates possess higher cohesive strength and do not fall apart: the finer ones melt completely, whereas, in the larger ones, the outer region melts and infiltrates the porous unmelted core which retains crystalline hexaferrite. Dense coatings can therefore be obtained while preserving high amounts of crystalline hexaferrite even inside the dense areas. Such coatings show magnetic properties that are promising for electromagnetic wave absorption applications.     

Synthesis,characterization and magnetic properties of polythiophene/SrFe12-x(ZrZn)0.5xO19 nanocomposite as a microwave absorber

Ferrites are an important group of magnetic materials which are used as absorbers. The incorporation of ferrite and conducting polymer achieves great enhancement in microwave absorption properties. The nanocomposites of hexagonal ferrites embedded by conducting polymers such as polypyrrole, polyaniline and polythiophene (PTH) have been paid much attention. In the present study, strontium hexagonal ferrite doped by Zr and Zn with the final formula of SrFe_12-x(ZrZn)_0.5xO19 considering x = 0.9 and embedded by PTH was produced to achieve a nanocomposite with the highest microwave absorbing ability. In this study, after synthesis of SrFe₁₂O₁₉(ZrZn)_0.5xO19 and PTH, the nanocomposite was prepared by in situ polymerization. Wrapping the ferrite particles and PTH chains could form nanocomposite properly, and therefore acceptable interactions were observable between SrFe_12-x(ZrZn)_0.5xO19ferrite particles and PTH polymer chains in the composites. Assessing the X-ray diffraction (XRD) patterns of SrFe_12-x(ZrZn)_0.5xO19, PTH, and PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite indicated that the PTH characteristic peak shifts slightly and its peak intensity reduces, which may be attribute to the coating of PTH polymer chains onto SrFe_12-x(ZrZn)_0.5xO19 particles. We revealed also lower magnetic properties in the obtained nanocomposite. The morphological assessment also suggested that PTH could effectively coat the SrFe_12-x(ZrZn)_0.5xO19 particles. The synergistic effect of SrFe_12-x(ZrZn)_0.5xO19 particle plus PTH leads to microwave absorption percentage higher than 95% by PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite. Overall, nanocomposite creating by coupling interaction between SrFe_12-x(ZrZn)_0.5xO19 particles (x = 0.9) and PTH can effectively lead to achieve the highest rate of absorption of electromagnetic waves.     

Low‐Temperature Sintering Li2MoO4/Ni0.5Zn0.5Fe2O4 Magneto‐Dielectric Composites for High‐Frequency Application

The coexistence of Li₂MoO₄ (LMO) and Ni_0.5Zn_0.5Fe₂O₄ (NZO) has been proven and their low‐temperature‐sintered magneto‐dielectric composites (1?x)LMO–xNZO (volume fraction factor x = 0.1, 0.3, 0.5, 0.7) were prepared by the conventional solid‐state reaction method and were sintered below 700°C. It is found that the optimal sample (x = 0.5) has good and relatively stable magneto‐dielectric performance in the frequency range from 10 MHz to 1 GHz with permittivity between 7.14 and 6.84, dielectric loss tangent between 0.09 and 0.02, and permeability between 5.23 and 3.30, magnetic loss tangent between 0.06 and 0.65, respectively. Furthermore, the verified chemical compatibility with silver indicates that the LMO–NZO ceramics are potential for low‐temperature cofired ceramic application and their multifunctional magneto‐dielectric properties also make them for potential applications in electronic devices.     

Enhanced Electrocaloric Effects in Spark Plasma‐Sintered Ba0.65Sr0.35TiO3‐Based Ceramics at Room Temperature

Improvement of electrocaloric effect was investigated in the lead‐free undoped and Mn‐doped Ba_0.65Sr_0.35TiO₃ ceramics prepared by spark plasma sintering process. Owing to the merit of spark plasma sintering process, a fully dense undoped and Mn‐doped Ba_0.65Sr_0.35TiO₃ ceramics with fine grain sizes could be obtained. The electrocaloric (EC) effect can be significantly enhanced from 0.83 K for conventional sintered Ba_0.65Sr_0.35TiO₃ to 3.08 K for spark plasma‐sintered Mn‐doped Ba_0.65Sr_0.35TiO₃ ceramics since the dielectric strength was dramatically increased. This work indicated an effective way to achieve the significantly enhanced EC effect in a lead‐free system at room temperature.     

High lithium ionic conductivity in the garnet‐type oxide Li7−2xLa3Zr2−xMoxO12 (x=0‐0.3) ceramics by sol‐gel method

Lithium garnet‐type oxides Li_7?2xLa₃Zr_2?xMo_xO₁₂ (x=0, 0.1, 0.2, 0.3) ceramics were prepared by a sol‐gel method. The influence of molybdenum on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X‐ray diffraction, scanning electron microscopy, and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Mo for Zr at low temperature. The introduction of Mo (x≥0.1) can accelerate densification. Li_6.6La₃Zr_1.8Mo_0.2O₁₂ sintered at lower temperature 1100°C for 3 hours exhibits highest total ionic conductivity of 5.09 × 10^?4 S/cm. Results indicate that the Mo doping LLZO synthesized by sol‐gel method effectively lowers its sintering temperature and improves the ionic conductivity.     

Exchange-coupling effect in hard/soft SrTb0.01Tm0.01Fe11.98O19/AFe2O4 (where A = Co,Ni, Zn,Cu and Mn) composites

In this study, series of hard/soft SrTb_0.01Tm_0.01Fe_11.98O₁₉/AFe₂O₄ (where A = Co, Ni, Zn, Cu and Mn) composites were fabricated via a single-pot citrate sol-gel approach. The structure, morphology and magnetic properties of prepared composite samples were investigated via X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM - TEM) and vibrating sample magnetometer (VSM). The XRD analysis of all composite samples showed the co-existence of both hard (Sr hexaferrite) and soft (spinel ferrites) ferrite phases with minor impurity. TEM micrographs displayed well-distinguished particles of SrM and AFe₂O₄ with different symmetry. The magnetic M − H hysteresis loops were performed at room temperature (RT; T = 300 K) and low temperature (T = 10 K) using VSM instrument. The magnitudes of various magnetic parameters including saturation magnetization (M_s), squareness ratio (SQR = M_r/M_s), remanence (M_r) and coercivity (H_c) were determined. M − H loops revealed smoothed curves and the dM/dH versus H curves exposed only a single peak, indicating that the exchange-coupling effect was accomplished in one-step. Moreover, the various composites showed relatively high M_s, M_r, and H_c values. The obtained results revealed the occurrence of exchange-coupling effect among soft and hard magnetic phases. The magnetic properties of various hard/soft SrTb_0.01Tm_0.01Fe_11.98O₁₉/AFe₂O₄ composites (where A = Co, Ni, Zn, Cu and Mn) were evaluated also by ZFC-FC magnetization measurements with respect to different soft phases. A peak temperature in ZFC curves occurred for various prepared composites. This peak is attributed to competition of the movement of magnetic domain walls and thermal activation. The present study offers a simple but efficient route for the fabrication of exchange-coupled nanocomposites with the chemical formula SrFe_11.98Tb_0.01Tm_0.01O₁₉/AFe₂O₄ (where A = Co, Ni, Zn, Cu and Mn) having controllable magnetic properties. It was found that the SrTb_0.01Tm_0.01Fe_11.98O₁₉/CoFe₂O₄ composite sample displayed the strongest exchange-coupling behavior among the different prepared composite products.     

Microwave Sintering of Nanocrystalline Ni1−xZnxFe2O4 Ferrite Powder and Their Magnetic Properties

Nanocrystalline Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying‐coprecipitation method. The obtained nanocrystalline Ni_1?xZn_xFe₂O₄ powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni_1?xZn_xFe₂O₄ ferrite powder. The initial permeability of Ni_1?xZn_xFe₂O₄ ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave‐sintered Ni_0.4Zn_0.6Fe₂O₄ ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni_1?xZn_xFe₂O₄ raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.     

Effect of Ga2O3 on Sintering and Phase Stability of Sc2O3‐Doped Tetragonal Zirconia Prepared via Aqueous Solution Route

The effects of the presence of Ga₂O₃ on low‐temperature sintering and the phase stability of 4, 5, and 6 mol% Sc₂O₃‐doped tetragonal zirconia ceramics (4ScSZ, 5ScSZ, and 6ScSZ, respectively) were investigated. A series of zirconia sintered bodies with compositions (ZrO₂)_0.99?x(Sc₂O₃)_x(Ga₂O₃)_0.01, x = 0.04, 0.05, and 0.06 was fabricated by sintering at 1000°C to 1500°C for 1 h using fine powders that were prepared via the combination of homogeneous precipitation method and hydrolysis technique using monoclinic zirconia sols synthesized through the forced hydrolysis of an aqueous solution of zirconium oxychloride at 100°C for 168 h. The presence of 1 mol% Ga₂O₃ was effective in reducing sintering temperature necessary to fabricate dense bodies and enabled to obtain dense sintered bodies via sintering at 1100°C for 1 h. The phase stability, that is, low‐temperature degradation behavior of the resultant zirconia ceramics was determined under hydrothermal condition. The zirconia ceramics codoped with 1 mol% Ga₂O₃ and 6 mol% Sc₂O₃ (1Ga6ScZ) fabricated via sintering at 1300°C for 1 h showed high phase stability without the appearance of monoclinic zirconia phase, that is the tetragonal‐to‐monoclinic phase transformation was not observed in the 1Ga6ScZ after treatment under hydrothermal condition at 150°C for 30 h.     

Role of exchange coupling between the hard and soft magnetic phases on the absorption of microwaves by SrFe10Al2O19/Co0.6Zn0.4Fe2O4 nanocomposite

(1-x)SrFe₁₀Al₂O₁₉/(x)Co_0.6Zn_0.4Fe₂O₄-(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by ‘one-pot’ self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of ?42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe₁₀Al₂O₁₉/(10 wt %)Co_0.6Zn_0.4Fe₂O₄ at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe₁₀Al₂O₁₉/Co_0.6Zn_0.4Fe₂O₄ nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz).