Bimagnetic hard/soft and soft/hard ferrite nanocomposites: Structural,magnetic and hyperthermia properties

Recent studies show that the chemical composition and shape of magnetic nanoparticles (NPs) play an important role in their properties. In particular, the bimagnetic NPs display useful and in many cases, more interesting properties than single-phase NPs. In this work, we prepared Fe₃O₄ and CoFe₂O₄ cube-like NPs and bimagnetic hard/soft (CoFe₂O₄/Fe₃O₄) and soft/hard (Fe₃O₄/CoFe₂O₄) nanocomposites (core/coating) using a facile and eco-friendly co-precipitation method that allows the synthesis of the cube-like NPs at temperatures near room temperature. The phase purity and the crystallinity of the NPs with a spinel structure were confirmed by the X-ray diffraction and infrared spectra techniques. Transmission electron microscopy (TEM) images revealed that the NPs have a cubic-like shape with an average dimension of 20 nm. Energy dispersive X-ray analysis, Mössbauer spectroscopy and SQUID magnetic measurements indicated the co-existence of Fe₃O₄ and CoFe₂O₄ phases in nanocomposites. In addition, the hysteresis loops exhibited a single-phase behavior in the nanocomposites that indicates there is a good exchange-coupling interaction between the hard and soft magnetic phases. The CoFe₂O₄/Fe₃O₄ nanocomposites presented a larger saturation magnetization than the CoFe₂O₄ NPs that is effective for their use in magnetic hyperthermia. Finally, we studied the hyperthermia properties of samples in an alternating magnetic field with a frequency of 276 kHz and field amplitude of 13.9 kA/m. Our results showed that magnetic hyperthermia efficiency simultaneously depends on the composition of samples along with magnetic anisotropy and saturation magnetization.     

Sol-gel synthesis of MnxGa1−xFe2O4 nanoparticles as candidates for hyperthermia treatment

Sol-gel synthesis of novel Mn_xGa_1−xFe₂O₄ (x=0–1) magnetic nanoparticles (MNP's) was studied. An inverse spinel crystalline structure was identified for all samples. Magnetization saturation values (Ms) were in the range of 21.4–42.6 emu/g, while coercive field (Hc) was less than 27.4 Oe in all cases. Selected compositions of Mn_xGa_1−xFe₂O₄ (x=0.6, 0.8) showed nanoparticles with near-spherical morphology and average size of 15 nm. Magnetic induction curves indicate that a suspension concentration of MNP's equal or higher than 4.5 mg/mL was sufficient to reach the temperature required for hyperthermia treatment (>43 °C) in less than 10 min. The incorporation of Mn ions into the crystalline structure led to an increase of the magnetic response of the MNP's when an alternate magnetic field was applied, requiring a shorter time of exposition and a low dose of MNP's, which make these nanoparticles potential candidates for magnetic hyperthermia.     

The simulation for a high-efficiency millimeter wave microstrip antenna by low dielectric loss and wide temperature stable lithium-based microwave dielectric ceramics for LTCC applications

As a common flux agent, B₂O₃–CuO was introduced into Li₂TiO₃ system to reduce the sintering temperature for the requirements of LTCC applications. The optimal mass ratio of CuO to B₂O₃ was innovatively explored. When the mass ratio of CuO to B₂O₃ increased to 1.2:1.0, excellent microwave dielectric properties were obtained in LTMF&LTZN_0.892+CB_1.2 ceramic of ε_r = 13.23, Q × f = 62,749 GHz, τ_f = -2.48 ppm/°C and the sintering temperature was reduced from 1300 to 930 °C. In a wide temperature range, the sample still maintain high temperature stability of |τ_f| < 5 ppm/°C (-40–120 °C). Based on the LTMF&LTZN_0.892+CB_1.2 substrate, a millimeter wave microstrip antenna resonated at 30.12 GHz was designed with a considerably high radiation efficiency of 93.94% and a signal gain of 4.87 dB. Comprehensive microwave dielectric properties make LTMF&LTZN_0.892+CB_1.2 become a candidate material for LTCC applications.     

Significant magnetoelectric enhancement of composite films of CoZnxFe2-xO4 particles and poly (vinylidene fluoride-trifluoroethylene) for AC magnetic sensors

Polymer-based magnetoelectric (ME) nanocomposites exhibit a low ME effect and high bias field at room temperature, which severely limits their application in flexible wearable sensors. To overcome these obstacles, Zn-doped magnetic nanoparticles of CoZn_xFe_2-xO₄ (x = 0, 0.1, 0.2, and 0.3) were prepared by an auto-combustion method in this work. The obtained magnetostrictive curves imply that Zn element doping can improve greatly the piezomagnetic coefficient of magnetic nanoparticles, and among the tested materials, CoZn_0.1Fe_1.9O₄ has the largest piezomagnetic coefficient. Composite films of poly(vinylidene fluoride-trifluoroethylene) and CoZn_0.1Fe_1.9O₄ (P(VDF-TrFE)/CoZn_0.1Fe_1.9O₄) were prepared by spin coating. The maximum ME voltage coefficient of P(VDF-TrFE)/CoZn_0.1Fe_1.9O₄ composite film with a filler weight concentration of 10 wt% is 87.9 mV cm⁻¹ Oe⁻¹ with a bias field of 1050 Oe and a resonance frequency of 46 kHz, which is the highest value reported in the literature of 0–3 type polymer-based ME composite films at present. To evaluate the composite films for application in magnetic sensors, the ME output voltage was measured at a bias field of 1050 Oe with increasing AC magnetic field, demonstrating a good linear relationship with linearity of 0.999. These results indicate that the piezomagnetic coefficient of magnetic materials is an the important factor for the great enhancement of the ME voltage coefficient. This work provides a new approach for the synthesis of more effective polymer-based ME nanocomposites for potential applications in smart wearables.     

Dielectric and magnetoelectric properties of BaTiO3–Co0.6Zn0.4Fe1.7Mn0.3O4 composite

In this paper we studied the structural, dielectric, magnetic and magnetoelectric properties of (x)BaTiO₃–(1 ? x)Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ particulate composite series where x = 0.50, 0.60 and 0.70. BaTiO₃–Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ composite has the advantage of being non-toxic and environmental friendly from the point of view of device fabrication. High ME voltage coefficients were obtained in the whole series with the highest value of α_E ～ 73 mV/cm Oe achieved in sample x = 0.50 containing equal mole fractions of both the component phases. This value of α_E is an order of magnitude higher than that of particulate sintered BaTiO₃–CoFe₂O₄ composites (～2–4 mV/cm Oe). Dielectric characteristics for these samples indicated two anomalies: (i) one at low temperature close to ferroelectric to paraelectric transition temperature of pure BaTiO₃ and (ii) another at higher temperature related to the magnetic transition in ferrite, a characteristic dielectric feature of composite sample.     

Structural,magnetic, and electrical evaluations of rare earth Gd3+ doped in mixed Co–Mn spinel ferrite nanoparticles

The controlled and stable crystal structure, reduction in Curie temperature and semiconducting nature of oxide materials are the key factors for magnetoelectrical applications. Therefore, Co_0.6Mn_0.4Gd_xFe_2-xO₄ where x = 0, 0.033, 0.066 and 0.10 were synthesized to analyse the structural, morphological, magnetic, and electrical properties using a sol-gel autocombustion approach. The X-ray diffraction pattern reveals that the cubic crystallite size decreases with increasing smaller content of Gd³⁺ oxides without any secondary phase. Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) study explain the complete morphology, agglomeration and dense structure of rare earth-doped Gd oxide in the mixed Co–Mn spinel ferrite nanoparticles. Fourier transform infrared spectra confirms the formation of a spinel structure with absorption bands below 1000 cm^?1. The magnetic analysis shows that the saturation magnetization (59.20 emu/g - 49.71 emu/g) and coercivity (985.21 Oe – 254.11 Oe) of the synthesized samples decreased with increasing content of Gd³⁺ ions. The increase in DC conductivity with increasing temperature verifies the semiconducting nature of the synthesized samples, and a higher DC conductivity of the Co_0.6Mn_0.4Gd_0.10Fe_1.90O₄(CMGF3) samples was observed at approximately 0.0362 S/cm at 973 K temperature.     

Ultra-low core loss FeSiAl soft magnetic composites with in-situ double oxidation layers of outer Fe3O4 layer and inner super-thin Al2O3/SiO2 hybrid layer

How to synchronously reduce eddy current loss and hysteresis loss still remains a challenge for achieving low core loss of soft magnetic composite (SMC). In-situ surface oxide effectively combines the formation of insulating layer and the release of internal stress during the molding process. In this study, FeSiAl SMC has been fabricated by powder metallurgy method with in-situ oxidated FeSiAl powder, in which FeSiAl powder are covered by outer Fe₃O₄ insulating layer and inter super-thin Al₂O₃/SiO₂ hybrid layer. Fe₃O₄ layer alleviates dilution magnetic effect, ensuring high saturated magnetization and effective permeability. The super-thin Al₂O₃/SiO₂ hybrid layer enhances electrical resistance, reducing eddy loss. Effects of the in-situ oxidation time on insulating layer and soft magnetic performances of SMC are investigated in detail. Synchronous reduction of eddy current loss and hysteresis loss is achieved through high resistance accompanied with proper insulating layer thickness and low coercive force provided by the special microstructure. For powder with 90 min oxidation at 500 °C, core loss of SMC is low up to 64 mW/cm³ at 50 mT and 100 kHz and 363 mW/cm³ at 100 mT and 100 kHz, while the permeability is kept at 50 until 1100 kHz and is stable until 140 °C. Meanwhile, DC bias performance reaches 51.2% at 100 Oe applied field and Q value is 104.8 at 400 kHz.     

High-performance 0.9Al2O3-0.1TiO2 microwave dielectric ceramics prepared by digital light processing

In this work, the 0.9Al₂O₃-0.1TiO₂ ceramic sample with good microwave dielectric properties and complex structures can be well fabricated by digital light processing (DLP). A relationship between dispersant content and rheological behavior of 0.9Al₂O₃-0.1TiO₂ slurry was explored. When dispersant content was 3.0 wt%, 0.9Al₂O₃-0.1TiO₂ slurry with high solid loading (50 vol%) and low viscosity (2.9 Pa s) could be obtained. 0.9Al₂O₃-0.1TiO₂ ceramic parts with high accuracy were fabricated successfully by adding 3.0 wt% photoinitiator under 600 mJ/cm² exposure energy. With the increase of sintering temperature from 1400 °C to 1600 °C, relative density, dielectric constant (ε_r), and quality factor (Q × f) of 0.9Al₂O₃-0.1TiO₂ ceramic sample increased first and then decreased, and all reached the maximum value at 1550 °C due to the uniformity and densification of microstructures. The temperature coefficient of resonant frequency (τ_f) value showed an almost monotonous increase, changing from negative to positive, and near-zero τ_f value at 1550 °C. In addition, 0.9Al₂O₃-0.1TiO₂ ceramic samples sintered at 1550 °C fabricated by DLP method presented much better microwave dielectric properties: ε_r = 11.30 ± 0.02, Q × f = 35,345 ± 143 GHz (@～12 GHz), τ_f = 2.16 ± 0.21 ppm/°C than that of by dry pressing method: ε_r = 11.16 ± 0.11, Q × f = 30,195 ± 257 GHz (@～12 GHz), τ_f = 4.45 ± 0.13 ppm/°C, especially the Q × f value achieved a 17% increase. Accordingly, DLP technique, which has advantages of producing relatively high properties and complex geometry of microwave dielectric ceramics as well as without extra high-cost mold, greatly satisfies application requirements.     

Structural transformation,dielectric and multiferroic properties of (Gd1-xBax)(Fe1-xTix)O3 ceramics by tuning composition

The structural transformation, ferro-paraelectric and magnetic ordering induced dielectric phase transitions, multiferroic properties, relaxation and conduction mechanisms of (Gd_1-xBa_x)(Fe_1-xTi_x)O₃ ceramics with different compositions (x = 0.0–0.4) have systematically been investigated. The chemical route is adopted for material synthesis. Rietveld refinement reveals the structural transformation from orthorhombic to mixed phase (coexistence of orthorhombic and tetragonal phase) for x > 0.2. The analysis of the FESEM micrographs suggests a decrease in average grain size with the increase in BT in the composition. Dielectric anomalies are explained based on ferroelectric-paraelectric phase transition of BaTiO₃, polarization induced by a spin reorientation, and antiferromagnetic ordering of GdFeO₃. The multiferroic properties of all the samples are studied from P-E, M-H, and magneto-electric plots. The improved magnetic properties in compositions x = 0.1–0.3, make them suitable candidates for spintronic devices. The maximum magneto-electric coupling coefficient of 4.77 mV/cm?Oe in the composition x = 0.3, makes it very much suitable for application in magnetoelectric coupling devices.     

Synthesis and magnetic properties of La3+-Co2+ substituted strontium ferrite particles using modified spray pyrolysis–calcination method

The purpose of the research was to improve the intrinsic magnetic properties of strontium ferrite by substituting lanthanum and cobalt for strontium and iron. The salt-assisted ultrasonic spray pyrolysis (SA-USP) following calcination process were used to from La-Co substituted strontium ferrite particles (La_xSr_1-xFe_12-yCo_yO₁₉), and their compositional dependent magnetic properties systemically investigated. All the samples were calcined at 1050 °C for 1 h in an air atmosphere to yield single-phased hexagonal particles several hundred nanometers to microns in size. A saturation magnetization of 70.76 emu/g and a coercivity 7265 Oe were obtained at a composition of La_0.25Sr_0.75Fe_11.75Co_0.25O₁₉. The amount of Co was reduced to obtain an optimized saturation magnetization of 71.40 emu/g and a coercivity of 7572 Oe at a composition of La_0.25Sr_0.75Fe_11.8Co_0.2O₁₉.     

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2 films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO₂ thin films using dc dual magnetron (DM) sputtering in Ar + O₂ mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature T_surf measured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency f_r was investigated in detail. It was found that the increase of f_r from 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate a_D of sputtered TiO₂ films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO₂ films can be sputtered on unheated glass substrates at a_D = 80 nm/min, T_surf < 180 °C when high value of f_r = 350 kHz was used. Properties of a thin hydrophilic TiO₂ film deposited on a polycarbonate substrate are given.     

A sonochemical method for synthesis of Fe3O4 nanoparticles and thermal stable PVA-based magnetic nanocomposite

Fe₃O₄ nanoparticles were synthesized via a simple surfactant-free sonochemical reaction. Room temperature synthesis without using inert atmosphere is the novelty of this work. The effect of different parameters on the morphology of the products was investigated. The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer. Fe₃O₄ nanoparticles exhibit a ferromagnetic behavior with a saturation magnetization of 66 emu/g and a coercivity of 39 Oe at room temperature. For preparation magnetic nanocomposite, Fe₃O₄ nanoparticles were added to the polyvinyl alcohol (PVA). Nanoparticles can enhance the thermal stability and flame retardant property of the PVA matrix.     

Synthesis and properties of TiO2 added NiNb2O6 microwave dielectric ceramics using a simple process

TiO₂ added NiNb₂O₆ ceramics produced using a reaction-sintering process were investigated. Pure columbite NiNb₂O₆ could be obtained without TiO₂ addition. With 30 and 40 mol% TiO₂ addition, a phase with the same structure of Ni_0.5Ti_0.5NbO₄ formed. Grain growth is easier in pellets with 30 and 40 mol% TiO₂ addition than in the NiNb₂O₆ pellets. Microwave dielectric properties: ?_r = 20.7, Q × f = 19,800 GHz (at 9 GHz) and τ_f = ?31.9 ppm/°C were obtained for NiNb₂O₆ pellets sintered at 1300 °C/2 h. ?_r around 45, Q × f = 5400–7700 GHz (at 6 GHz) and τ_f ～ 73 ppm/°C were obtained in pellets with 30 mol% TiO₂ addition. ?_r around 50, Q × f = 3800–5700 GHz (at 6 GHz) and τ_f ～ 99 ppm/°C were obtained in pellets with 40 mol% TiO₂ addition.     

Phase formation and magnetic properties of M-type lanthanum substituted strontium ferrites

Rare earth ion substitution is one of the most important methods for adjusting the magnetic properties of M-type hexagonal ferrites; however, the regularity of these phase formations has rarely been studied. In this work, La substituted Sr hexaferrite La_xSr_1-xO·nFe₂O₃ (La-SrM, 4.9 ≤ n ≤ 6.0, 0 ≤ x ≤ 0.6) was prepared using the traditional ceramic method. The effects of the Fe/Sr molar ratio (n), calcining temperature, and La³⁺ substitution (x) on SrM phase formation, the crystalline structure, and magnetic properties were investigated. With an increase of x up to a maximum value of 0.5–0.6, a higher calcining temperature is required to form the single M-phase of La-SrM samples. However, the optimal n values of single-phase La-SrM samples differ as the La substitution varies: when x = 0.1, n = 5.5–6.0; x = 0.2, n = 5.5–5.9; x = 0.3, 0.4 and 0.5, n = 5.7–5.8. The magnetic measurements show that La_0.2Sr_0.8O·5.8Fe₂O₃ has the highest specific saturation magnetization (σ_s), which is 2.2% higher than that of unsubstituted SrM (SrO·6Fe₂O₃), while the anisotropic field (H_A), the anisotropic constant (K₁), and Neel point (T_N) of La³⁺ substituted SrM decreased. Detailed structure analyses were conducted to explain the changes in magnetic properties. Fe³⁺ in the spin-up 2a sublattice of La_xSr_1-xO·5.8Fe₂O₃ decreased by approximately 5% from 98.5% (x = 0) to 93.85% (x = 0.4) with an increase in x. Additionally, a small amount of Fe³⁺ was reduced to Fe²⁺ in the spin-down 4f₂ sublattice with the maximum reduction amount of 4.13% reached at x = 0.2, thereby improving σ_s. The decrease in the bond angle of (4f₁) Fe3–O2–Fe5 (12k), (2a) Fe1–O4–Fe3 (4f₁), and (4f₁) Fe3–O4–Fe5 (12k) lead to the weakening of Fe–O–Fe superexchange of La-SrM so that H_A, K_1, and T_n decreased with increasing values of x. This work lays a solid foundation for the study of process regulation and ion substitution of permanent magnet ferrite.     

Electrical and magnetic properties of magnesium-substituted lithium ferrite

Magnesium-substituted lithium ferrite of different composition (Li_0.5Fe_2.5−xMg_xO_4−δ) were prepared for x = 0.0–1.0 by conventional ceramic technique. The crystal structure characterization and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). Initial permeability and quality factor were measured in the frequency range of 1 kHz to 100 MHz. The permeability decreased gradually from μ (f = 10 MHz) = 34.0 for Li_0.5Fe_2.5O₄ to μ (f = 10 MHz) = 11.5 for Li_0.5Fe_1.5Mg_1.0O₄. Electrical conductivity measurements were carried in the range of 250–700 °C in air. The maximum electrical conductivity, σ_700 °C = 0.1274 S/cm has been found to be for Li_0.5Fe_2.5O₄ specimen. With increasing Mg-substituted content, the decreased in the electrical conductivity.     

Shielding properties of CuNiZn ferrite in the radio frequency range

Shielding properties of copper-doped NiZn ferrites in the frequency range 1 MHz–1.8 GHz, were explored. Samples of composition Cu_xNi_0.4?xZn_0.6Fe₂O₄ with x=0.0, 0.1, 0.2, 0.3 and 0.4, were prepared by the ceramic method. Powders and pellets were sintered at 1100 °C for 2 h. The effect of compositional variation on structural, dielectric and magnetic properties was investigated in order to relate them with the attenuation behavior. X-ray diffraction measurements confirmed the formation of a spinel structure at the selected sintering temperature. The addition of copper promotes grain growth, increases the samples density and modifies saturation magnetization, permeability and permittivity in the explored frequency range. As the reflection loss absolute values (|R_L|) for all the samples are above 35 dB, they can all be considered as shielding materials. The optimum attenuation was observed for x=0.2, reaching a maximum |R_L| of almost 60 dB at 10 MHz with an attenuation bandwidth of at least 3 MHz.     

Low‐Temperature Sintering and Microwave Dielectric Properties of ZnNb2O6–TiO2 Ceramics with BaCu(B2O5) Additions

The influence of BaCu(B₂O₅) (BCB) on densification, phases, microstructure and microwave dielectric properties of ZnNb₂O₆–xTiO₂ (x = 1.70–1.90) composite ceramics have been investigated. Undoped ZnNb₂O₆–1.8TiO₂ ceramics sintered at 1200°C exhibit temperature coefficient of resonant frequency (τ_f) ~9.25 ppm/°C. When BaCu(B₂O₅) was added, the sintering temperature of the ZnNb₂O₆–1.8TiO₂ composite ceramics was effectively reduced to 950°C. The results indicated that the permittivity and Q × f were dependent on the sintering temperature and the amounts of BaCu(B₂O₅). Addition of 3.0 wt% BaCu(B₂O₅) in ZnNb₂O₆–1.8TiO₂ ceramics sintered at 950°C showed excellent dielectric properties of ε_r = 40.9, Q × f = 12,200 GHz (f = 5.015 GHz) and τ_f = +0.3 ppm/°C.     

Bismuth titanates candidates for high permittivity LTCC

Bi₂O₃–TiO₂ composites are known to possess attractive microwave dielectric properties. However, producing LTCC analogues with equally promising dielectric properties is problematic. Here, we show that judicious choice of both TiO₂ starting powders and dopants can produce composites with excellent properties. Three TiO₂ powders were evaluated: 1 μm-anatase, 1 μm-rutile and a nanosized (30 nm) mixture of 75–25 anatase-rutile. The best dielectric properties were obtained by using uncalcined nanosized anatase/rutile with Bi₂O₃ powder. By doping this Bi₂O₃–TiO₂ powder mixture with 0.112 wt.% CuO dielectric properties of Q × f = 9000 GHz, ɛ_r = 80 and τ_f = 0 ppm/K (at 300 K) were obtained at a sintering temperature of 915 °C.     

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.     

Room temperature magnetoelectric coupling study in multiferroic Bi4NdTi3Fe0.7Ni0.3O15 prepared by a multicalcination procedure

Single-phase Bi₄NdTi₃Fe_0.7Ni_0.3O₁₅ polycrystalline samples were synthesized following a multicalcination procedure. The sample exhibited multiferroic property at room temperature, which was demonstrated by the ferroelectric (2P_r=8.52 μC/cm², 2E_c=89 kV/cm at applied electric field 110 kV/cm) and magnetic (2M_r=388 m emu/g, 2H_c=689 Oe at applied magnetic field 1.04 T) hysteresis loops. More importantly, magnetoelectric coupling effect is observed from measurements of electrical properties not only under small but also under large electric signal when an external magnetic field is applied. The present results suggest a new candidate for a room temperature multiferroic material with magnetoelectric coupling effect.