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Currently, semiconductor–relaxor ferroelectric (0–3) type composites are promising lead-free ferroelectric candidates for high-temperature piezoelectric applications. Among all, 0.30(ZnO)-0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3] is one of the most studied composites by researchers. Therefore, to understand the role of ZnO on the polarization reversal process and domain states of (Bi0.5Na0.5)0.94Ba0.06TiO3, the dynamic ferroelectric hysteresis of the present composite has been investigated as a function of electric field amplitude (E0) and frequency (f). According to the power law, a set of scaling relations between the loop area ⟨A⟩ with E0 and f have been established for minor and saturated loops, which take the form of ⟨ A ⟩ ∝ f − 0.389 E 0 4.586 and ⟨ A ⟩ ∝ f − 0.021 E 0 1.066 , respectively. Also, it is interesting to note that the frequency-dependent ferroelectric hysteresis loops [for the saturated field (E0) = 50 kV/cm] exhibit the unique two-stage scaling behavior. Additionally, the origin of enhancement in the domain switching process for minor loop regions has been correlated with the presence of a semiconductor (ZnO), which is extensively discussed in the present study. [ABSTRACT FROM AUTHOR]

Composites of barium hexaferrite (BaFe 12 O 19) and nickel zinc ferrite (Ni 0.5 Zn 0.5 Fe 2 O 4) have been prepared by the high-energy planetary ball mill method. The magnetic composites are characterized by employing X-ray Diffraction and High-Resolution Transmission Electron Microscopy (HRTEM) techniques. The percentage of barium hexaferrite (BaFe 12 O 19) and nickel zinc ferrite (Ni 0.5 Zn 0.5 Fe 2 O 4) in the composite has been obtained from the Rietveld analysis of XRD patterns. The average crystallite sizes of BHF and NZFO are found to be comparable in the composites. The magnetic properties of (1-x) BHF-(x) NZFO with x = 0 to 1 have been studied by measuring the magnetic hysteresis loop (M-H loop) for all the samples. The M-H loops are analyzed by plotting the loop width (ΔH) versus magnetization (M). The magnetic hysteresis loops for the BHF and NZFO are found to be symmetric in all the quadrants. However, symmetry breaks in M-H loops for composites. The symmetry breaking in magnetic hysteresis loops of the bi-magnetic composite suggests a new approach to analyzing the magnetic interaction between magnetic phases in the magnetic composites. [ABSTRACT FROM AUTHOR]

In view of tuning different transitions, Co and V are substituted in Mn-rich Ni-Mn-Ga alloy. Ni41Co9Mn30V2Ga18 sample undergoes a coupled magnetostructural transition above room temperature with a low thermal and magnetic hysteresis and high sensitivity of martensite transition temperature (8 K/T) with the field. ∆SM is found to be a maximum of −2.33 J/kg-K for 3 T field change with a large RCP of 158 J/kg. The presence of intermartensite transition along with the magnetostructural transition widens the range of working temperature. [ABSTRACT FROM AUTHOR]

This paper reports on reduced graphene oxide (rGO), tin oxide (SnO2) and polyvinylidene fluoride (PVDF) tertiary nanocomposite thick film based flexible gas sensor. The nanocomposite of 0.90(PVDF) − 0.10[x(SnO2) − (1 − x)rGO] with different weight percentages (x = 0, 0.15, 0.30, 0.45, 0.6, 0.75, 0.90 and 1) have been prepared by the hot press method. Chromium (Cr) has been deposited on the surface by using E-beam evaporation system, which is used as electrode of the device. Crystal structure, morphology, and electrical characteristics of the device have been explored for the technological application. A correlation between crystallinity, morphology, and electrical properties with these thick films has also been established. The device has been tested at different hydrogen (H2) gas concentration as well as at different response times. A superior response of 0.90(PVDF) − 0.10[0.75(SnO2) − 0.25 rGO] nanocomposite thick film has been observed. Hence, this composition is considered as optimized tertiary nanocomposite for the hydrogen gas sensor application. The sensor response of 49.2 and 71.4% with response time 34 sec and 52 sec for 100 PPM and 1000 PPM H2 gas concentration respectively have been obtained. First time a new kind of low cost and flexible polymer based nanocomposite thick film gas sensor has been explored. [ABSTRACT FROM AUTHOR]

An interfacial integration at the nanoscale domain through a core@shell (CS) nanostructure has constructively unbarred a wide dimension to researchers on biomedical applications, especially for magnetic fluid hyperthermia. Lately, the interconnection of the exchange bias effect (EBE) through the interface coupling to the magnetic heating efficiency has uttered its utmost prominence for researchers. Here, we delineate the ascendency of the heating ability through a coalescing assembly of mixed ferrite Co0.5Zn0.5 Fe2O4 (CZ) and soft magnetic material Fe3O4 (F), by devising a network of CoZnFe2O4@Fe3O4 (CZF) CS nanostructure. A hefty interface activity with validation of the EBE phenomenon is divulged through magnetic scrutiny for the CS sample. The magnetic nanoparticles heating response to applied magnetic field and frequency is discerned at three distinct fields, where the outcome prevailed to inflated specific loss power for CS CZF in distinction to bare F and CZ samples for all the assessments. Remarkably; a lofty intrinsic loss parameter is also perceived for the CS sample recorded to about 5.36 nHm2 g−1; which is another eccentric outcome that significantly labels the CS CZF sample as a potentially high heating competence agent. This comprehension accords to a finer perspective to meliorate the theranostic environment for hyperthermia applications. [ABSTRACT FROM AUTHOR]

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (| Δ S M max |) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (R C effe ) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ 2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases. [ABSTRACT FROM AUTHOR]

An interfacial integration at the nanoscale domain through a core@shell (CS) nanostructure has constructively unbarred a wide dimension to researchers on biomedical applications, especially for magnetic fluid hyperthermia. Lately, the interconnection of the exchange bias effect (EBE) through the interface coupling to the magnetic heating efficiency has uttered its utmost prominence for researchers. Here, we delineate the ascendency of the heating ability through a coalescing assembly of mixed ferrite Co0.5Zn0.5 Fe2O4 (CZ) and soft magnetic material Fe3O4 (F), by devising a network of CoZnFe2O4@Fe3O4 (CZF) CS nanostructure. A hefty interface activity with validation of the EBE phenomenon is divulged through magnetic scrutiny for the CS sample. The magnetic nanoparticles heating response to applied magnetic field and frequency is discerned at three distinct fields, where the outcome prevailed to inflated specific loss power for CS CZF in distinction to bare F and CZ samples for all the assessments. Remarkably; a lofty intrinsic loss parameter is also perceived for the CS sample recorded to about 5.36 nHm2 g−1; which is another eccentric outcome that significantly labels the CS CZF sample as a potentially high heating competence agent. This comprehension accords to a finer perspective to meliorate the theranostic environment for hyperthermia applications. [ABSTRACT FROM AUTHOR]

Strontium (Sr) substituted cobalt ferrite i.e. Co 1− x Sr x Fe 2 O 4 ( x =0.00, 0.01, 0.015, 0.02, 0.05, 0.1) have been synthesized by the citric acid modified sol–gel method. Crystal structure and phase purity have been studied by the X-ray powder diffraction technique. The Rietveld refinement of XRD pattern using the space group F d 3 ¯ m shows monotonically increasing of lattice parameter with the increase in Sr concentration. Magnetic hysteresis loops measurement has been carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±1.5 T. Magnetocrystalline anisotropy constant were calculated by employing the Law of Approach (LA) to the saturation. It is observed that magnetocrystalline anisotropy has anomaly for x =0.01 (Co 0.99 Sr 0.01 Fe 2 O 4 ) sample. Strain mediated modification of magnetic properties in Sr substituted cobalt ferrite has been observed. The saturation magnetization for doping concentration i.e. x =0.01 abruptly increase while for x >0.01 decreases with the increase in Sr concentration. A correlation between lattice strain and magnetic behavior in non-magnetic Sr- substituted nano-crystalline cobalt ferrite has been reported. [ABSTRACT FROM AUTHOR]

Strontium hexaferrite is a hard magnet that can help to develop rare-earth-free magnets for permanent magnet applications. A composition of SrFe 12-x-y Ni x Al y O 19 (0.005 ≤ x ≤ 0.02; 1 ≤ y ≤ 4) is successfully synthesized with by the sol-gel auto-combustion process, and the effect of Ni-Al substitution is studied on the structural, magnetic, dielectric, and electrical properties. The XRD analysis confirms the formation of magnetoplumbite hexagonal structure with P6 3 / mmc space group. Magnetic studies have shown a massive improvement in the coercivity (H c) of the samples. The highest ever H c value of 24.44 kOe in strontium hexaferrite-based rare-earth free magnet is attained for the SrFe 7.98 Ni 0.02 Al 4 O 19 ferrite composition. The energy density (BH) max is effectively tuned to 16.2 MGOe for the SrFe 8.985 Ni 0.015 Al 3 O 19 composition. The dielectric properties have shown the typical behavior of ferrites and are explained according to the Maxwell-Wagner and Koop model. The proposed work is expected to offer an immense possibility to improve the hard magnetic properties of strontium hexaferrite magnets comparable to the expensive NdFeB magnets in order to fully/partially replace them in different permanent magnet applications. [Display omitted] • An attempt to substitute Ni2+ & Al3+ ions at Fe3+ lattice site in SrFe 12 O 19 ferrite. • Highest ever H c value of 24.44 kOe is attained for SrFe 7.98 Ni 0.02 Al 4 O 19 composition. • Found an enhanced (BH) max value ∼16.2 MGOe for SrFe 8.985 Ni 0.015 Al 3 O 19 composition. • These ferrites offer the utmost probability to use in different PM applications. • This work suggests the exploration of SrM to improve its hard magnetic properties. [ABSTRACT FROM AUTHOR]

• Maximum (BH) max and reduced remanent are found to be 0.887 MGOe and 0.53, respectively, for (50)%BHF+(50)%CFO composite. • Exchange coupling is responsible for enhanced (BH) max and reduced remanent in the composite. • Henkel plot and derivative of magnetization vs field curve are used to explore the magnetic interaction between particles. The (x)% BaFe 12 O 19 (BHF) + (100-x)% CoFe 2 O 4 (CFO) (x = 0 to 100) magnetic composites are prepared to explore its magnetic properties. The XRD patterns reveal the presence of both BaFe 12 O 19 and CoFe 2 O 4 crystal symmetries in the composite. The FESEM and TEM micrographs reveal the uniform distribution of nanoparticles. The theoretical saturation magnetization is calculated by Vegard's law, which is nearly equal to the experimental observation. The maximum reduced remanent (M r /M s) and magnetic energy product (BH) max are found to be 0.43 and 0.456 MGOe, respectively, for x = 50 i.e. (50)% BHF + (50)% CFO. It is explained by assuming magnetic interaction at the interfaces of soft and hard magnetic phases. The coercive field, remannet magnetization, reduced remanent, saturation magnetization, and (BH) max increase with a decrease in measuring temperatures. The enhancement of magnetic parameters at a low temperature is observed due to the decrement of the thermal energy of magnetic moments at the surface. The saturation magnetization increases with an increase in annealing temperature, which could be due to the minimization of spin disorders at the surface of nanoparticles. The enhanced reduced remanent (M r /M s) and (BH) max are found for the (50)%BHF + (50)%CFO composite annealed at a higher temperature. The evidence of magnetic interaction between two magnetic phases in the composite has been realized by employing the Henkel plots and dM dH versus H curve techniques. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles of calcium (Ca)-substituted cobalt ferrite i.e. Co 1− x Ca x Fe 2 O 4 ( x =0.00, 0.01, 0.015, 0.02, 0.05, 0.1, and 0.15) have been synthesized by the citric acid modified sol–gel method. X-ray powder diffraction (XRD)patterns confirm the formation of spinel phase. The particle size decreases with the Ca concentration. The Rietveld refinement of XRD patterns using the space group – Fd 3 ̅ m shows monotonically increasing of lattice parameter with the increasing concentration of Ca. The FT-IR spectrum recorded in the range of 325–1000 cm −1 and Raman spectrum obtained in the range of 88–800 cm −1 shows the formation of spinel phase belonging to Fd 3 ̅ m space group supporting structural analysis from XRD patterns. Magnetocrystalline anisotropy has been obtained using “Law of Approach (LA) to Saturation magnetization”. Saturation magnetization and remnant magnetization is maximum for 1% Ca substitution which could be due to strain mediated magnetism. However these magnetic properties decrease with the Ca substitution for the percentage above 1%. It could be due to decrease of magnetic exchange interaction in the sample. A correlation between magnetic behavior and lattice strain has been established in non-magnetic Ca substituted nano-crystalline cobalt ferrite. In order to investigate the ferromagnetic nature of the sample, Arrott plot analysis has been carried out. Difference in saturation magnetization obtained from LA to saturation and Arrott plot analysis gives the qualitative information about the influence of lattice strain on saturation magnetization. [ABSTRACT FROM AUTHOR]

Beside the disappearance of characteristics superlattice reflections for R 3 c space group as (1 1 3) at 2θ =37.8°, the typical reflections of Pbnm space group as (1 1 1) at 2θ =25.42° as well as their new superlattice reflections such as (0 2 1), (0 2 3) and (2 2 1) at 2θ =34.14°, 47.69° and 47.82° which are characteristic of the antiparallel cation displacements has appeared for 7.5% of co-substitution (Eu in Bi site and Mn in Fe site) in BiFeO 3 . Morphological phase boundary has been observed around 7.5% of co-substitution which have enhanced remnant magnetization about 20 times that of pure one and it could be due to the suppression of cycloid spin structure and spin canting at the surface of nanocrystallites. Further increase in co-substitution percentage (>7.5%) leads to the reduction of remnant magnetization due to the appearance of collinear antiferromagnetic ordering in the Pbnm space group which becomes significant for higher co-substitution percentage. The analysis of diffuse reflectance spectra which shows the point group symmetry breaking from O h to C 3v supports the modification in local FeO 6 environment and structural transition. [ABSTRACT FROM AUTHOR]

Bi 1− x La x Fe 1− x Mn x O 3 ( x = 0.000–0.300) ceramics prepared by the tartaric acid modified sol–gel technique have been studied to analyze the effect of composition driven structural transition on the magnetic properties of bismuth ferrite (BiFeO 3 ). It was found that the co-substitution of La & Mn at Bi & Fe sites leads to suppression of impurity phases (Bi 2 Fe 4 O 9 and Bi 25 FeO 40 ) which generally appear in BiFeO 3 . The quantitative crystallographic phase analysis has been carried out by double phase Rietveld analysis of all the XRD patterns which indicates the existence of compositional driven crystal structure transformation from rhombohederal (space group R3c ) to the orthorhombic (space group Pbnm ) with the increase in substitution concentration. The 5% co-substituted sample exhibit high remnant magnetization i.e. about 15 times that of BiFeO 3 which is due to the suppression of cycloid spin structure and enhanced canting angle of antiferromagnetically ordered spins caused by the crystal lattice distortion. However, further increase in substitution results in the reduction of remnant magnetization and coercivity due to the appearance of complete antiferromagnetic ordering in the orthorhombic structure because of the significant contribution from the crystallographic phase of Pbnm space group (as obtained from double phase Rietveld analysis). The frequency independent higher dielectric constant and lower dielectric loss were observed for 5% co-substitution. Hence, this particular composition may be interesting for device applications. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of Bi1-xNdxFe1-xMnxO3 ceramics prepared by the tartaric acid modified sol-gel technique have been studied to understand the effect of structural modification on the magnetic Properties of BiFeO3. The co-substitution of Nd and Mn at Bi and Fe sites respectively in BiFeO3 significantly suppress the impurity phases (Bi25FeO40, Bi2Fe4O9 etc.). The Rietveld analysis of X-ray diffraction (XRD) patterns indicates the existence of compositional driven crystal structure transformation from rhombohederal (R3c space group, higher crystal symmetry) to the orthorhombic (Pbnm space group, lower crystal symmetry) with the increase in substitution concentration due to excess chemical pressure (lattice strain). The quantitative crystallographic phase analysis has been carried out by Rietveld analysis of all the XRD patterns. Magnetic measurements reveal that co-substituted BiFeO3 nanoparticles for x=0.050 have enhanced remnant magnetization about 21 times as compared to pure one. The remnant magnetization reaches a maximum value at the morphological phase boundary (x=0.050) and further increase (x>0.050) in substitution concentration results in the reduction of remnant magnetization due to the appearance of complete antiferromagnetic ordering in the orthorhombic structure because of the significant contribution from the crystallographic phase of Pbnm space group (as obtained from the quantitative crystallographic phase contribution by the Rietveld analysis). [ABSTRACT FROM AUTHOR]

• Gadolinium doping in BHF results in modification of magnetic properties. • "Law of Approach to Saturation" gives the magnetocrystalline anisotropy constant. • Para-ferrimagnetic transition is observed around 700 K. • Maximum entropy change and RCP are found to be 0.72 J/kgK and 27.5 J/kg, respectively, near Curie temperature. • Possibility to use the Gd doped BHF at high temperature as a cooling agent. Gd doped barium hexaferrite (BaFe 12−x Gd x O 19 , x = 0.0–0.7) has been synthesized by the sol-gel method to explore its magnetic and MCE (magnetocaloric effect) properties. The materials crystallize to hexagonal magnetoplumbite phase. Average particle size decreases with the increase in Gd concentration in barium hexaferrite (BHF). The coercive field increases from 3.2 to 4.8 kOe, and saturation magnetization decreases from 68.21 to 54.23 emu/g with the increase in Gd concentration from x = 0.0 to x = 0.7. These large changes in magnetic parameters reveal the effect of Gd concentration in BHF. The saturation magnetization monotonously reduces with an increase in Gd concentration in BHF due to a decrease in average particle sizes. The saturation magnetization is found to be higher at a lower temperature (60 K) compared to that of room temperature (300 K). It is due to a reduction in thermal energy at low temperature which is smaller compared to the magnetic Gibbs free energy at low temperature. Hence, the magnetic spins are freezing along the applied magnetic field direction at the low temperature. Also, the magnetocrystalline anisotropy constant (obtained by the "Law of Approach to Saturation method") is found to be more at low temperature compared to that of room temperature due to an increase in the strength of spin-orbit coupling with the decrease in temperature (i.e. thermal energy). The M-T curves and M-H hysteresis loops reveal paramagnetic to ferromagnetic transition at the Curie temperature. The maximum entropy change was found to be in the range of 0.12–0.72 J/kgK in a window of the applied magnetic field of 0.5–3 T, and the corresponding RCP max was found to be 2.5–27.5 J/kg. The present study opens a window to explore the MCE on BHF based material. [ABSTRACT FROM AUTHOR]

With an aim to explore the d0 ferromagnetism in Ag-doped ZnO compounds, the poly-crystalline samples of Zn 1 - x Ag x O (with 0 ≤ x ≤ 0.12) were synthesized by a standard solid-state synthesis technique. The XRD analyses indicated that these compounds have been formed as Ag:ZnO nanocomposite. According to scanning electron microstructural study, all compounds have a homogenous nearly spherical shape morphology. The EDS spectra reveal that the final produced compounds do not contain any unwanted external impurity. The magnetization versus field measurement at room temperature demonstrates that the undoped ZnO compound shows ferromagnetism embedded in diamagnetic matrix, whereas all Ag-doped ZnO samples exhibit a clear room temperature ferromagnetic behavior with coercivity values between 80 and 196 Oe. The maximum saturation magnetization was obtained for the Zn0.97Ag0.03O sample; however, it declines subsequently. The bound magnetic polarons (BMPs) has been considered to explain the observed ferromagnetic behavior. [ABSTRACT FROM AUTHOR]

[Display omitted] • Successful synthesis of PVP capped doped CuS quantum dots. • A marked increase in the band gap of the quantum dots. • Low field magnetic interactions at room temperature. Polyvinlypyrrolidone (PVP) capped and magnetic transition metals (TM = Fe, Co and Cr) doped CuS quantum dots (Cu 1- x TM x S; x = 0.02 & 0.04) were synthesized by low entropy facile chemical co-precipitation method. The structural, optical and magnetic characterizations of the synthesized QDs were done by using X-ray diffraction (XRD) technique, UV–Vis-NIR absorption spectroscopy, photoluminescence (PL) spectroscopy and superconducting quantum interference device (SQUID) respectively. The low field non-linearity and the presence of coercivity in the M−H loops indicate the presence low field magnetic (spin–spin) interactions between the doped cations. [ABSTRACT FROM AUTHOR]

We report ferromagnetic behavior in undoped ZnO nanofibers prepared by electrospinning a solution of zinc acetate and poly vinyl alcohol followed by annealing at 550°C for about 90min. X-ray diffraction patterns of the heat treated as-spun composite fibers reveal the formation of ZnO nanowires in wurtzite structure with no noticeable impurity phases. ZnO nanowires annealed between 500°C and 600°C exhibited room temperature ferromagnetism with decreasing magnetization with increasing annealing temperature. Room temperature ferromagnetism was observed in as-spun fibers annealed in air as well as under vacuum. However, vacuum annealed nanofibers show higher magnetization as compared to air annealed fibers, which indicates that oxygen vacancy is a cause for the observed room temperature ferromagnetism in the ZnO nanofibers. [ABSTRACT FROM AUTHOR]

The (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 (0-3 type particulate) nanocomposites with x = 0.00, 0.02, 0.04, 0.06, 0.08, and 1.00 were prepared by the solid-state method. Cobalt ferrite crystallized into cubic crystal symmetry with an F d 3 ̄ m space group. Strontium-substituted barium titanate crystallized into a tetragonal crystal structure with a P4mm space group. Field emission scanning electron microscopy and transmission electron microscopy techniques show the distribution of different sizes of particle. Polarization vs electric field curves show the highest maximum polarization (Pm) of 10.26 μC/cm2, remnant magnetization (Pr) of 11.70 μC/cm2, and coercivity (Ec) of 19.95 kV/cm for x = 0.04 composition at 35 kV/cm. However, it is smaller than the Ba0.8Sr0.2TiO3 phase (Pm = 16.86 μC/cm2, Pr = 13.20 μC/cm2, and EC = 10.80 kV/cm). The highest dielectric constant of around 9800 was found for x = 0.04 composition, with a very small dielectric loss factor of about 0.02, i.e., less than even 2%. This is ∼10 times compared to that of Ba0.8Sr0.2TiO3 (BSTO), which has been explained by considering interaction at the interface of CoFe2O4 (CFO) and BSTO, leakage current, and variation of the lattice parameter of BSTO in (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 nanocomposite. The magnetic hysteresis loops show squeezing near the origin. The magnetic parameters like coercivity, remnant magnetization, and saturation magnetization increased with the increase in the CoFe2O4 weight fraction. Magnetic interaction between surfaces of magnetic CFO and non-magnetic BSTO is evident from the ΔH vs M plots, and it also evidences the magnetism at the surface of BSTO due to uncompensated spins. [ABSTRACT FROM AUTHOR]

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12-xAlxO19, x=0.0-4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution. [ABSTRACT FROM AUTHOR]

Lead-free ferroelectric materials are essential for environment-friendly solid-state cooling technology. In this respect, the electrocaloric effect of lead-free Ba0.8−xSr0.2SmxTiO3 (x = 0.01–0.05) ceramics has been investigated. The Rietveld refinement reveals that all the ceramics exhibit tetragonal symmetry and the tetragonality decreases for x > 0.03, which is the major reason behind the decrease in both isothermal entropy change and adiabatic temperature change. The degree of diffuseness parameter is enhanced by doping of Sm3+, which confirms the formation of polar nanoregion and the enhancement of the electrocaloric effect parameter by adding extra entropy. The relaxor behavior of the prepared samples is also confirmed by estimating the degree of deviation parameter (Δ T m = 77 K ) from the 1 ε r vs. T curve. So, the temperature stability of the prepared ceramics is improved in a broad temperature window. The highest isothermal entropy change (Δ S) , adiabatic temperature change (Δ T) , and electrocaloric strength ( Δ T Δ E ) are found to be 1.230 Jkg−1 K−1, 0.862 K, and 0.028 73 K cm/kV at 316 K, respectively, for Ba0.77Sr0.2Sm0.03TiO3. [ABSTRACT FROM AUTHOR]

The CoFe2-xMnxO4 compound is prepared by following the sol gel technique. The structural analysis through XRD and Rietveld has been confirmed for the single cubic phase having ... space group for CoFe2-xMnxO4 and also verified it through Raman spectroscopy measurements. The tetrahedral site observed to be red shifted with increase in Mn concentration in cobalt ferrite. All the XRD patterns have been analyzed by employing the Rietveld refinement technique. The particle size was found to be in the range of 30-40 nm. The electrical properties of polycrystalline CoFe2-xMnxO4 for x=0.00, 0.10, 0.15, and 0.2, spinel ferrite was investigated by impedance spectroscopy. The influence of doping, frequency and temperature on the electrical transport properties of the CoFe2-xMnxO4 for x=0.00, 0.10, 0.15, and 0.20 were investigated. The magnitude of Z' and Z" decreases with increase in temperature. Only one semicircle is observed in each Cole Cole plot which reveals that ac conductivity is dominated by grains. The grain resistance and grain boundary resistance both were found to decrease as a function of temperature. Temperature variation of DC electrical conductivity follows the Arrhenius relationship. A detailed analysis of electrical parameters provides assistance in connecting information regarding the conduction mechanism as well as determination of both dielectric and magnetic transition temperatures in the substituted cobalt ferrite. Detailed analysis of ac impedance and DC resistivity measurement reveals that, the magnetic ordering temperature in the Mn substituted cobalt ferrite does not respond to the frequency of ac electrical signal; however, it responds to the DC resistivity. The correlation between ac impedance and DC resistivity has been established. [ABSTRACT FROM AUTHOR]

Polycrystalline [(0.5) Bi0.5Na0.5TiO3-(0.5) LaFeO3] multiferroic composite is prepared by using the solid-state reaction method. The crystal structure of both phases is characterized by using the X-ray diffraction method (XRD) and confirms the presence of rhombohedral (i.e., bismuth sodium titanate) and orthorhombic (i.e., lanthanum ferrite) phases in the composite. The microstructure of the composite is analyzed using field emission scanning electron microscopy (FESEM). The crystal structure is further studied with Raman spectroscopy. The present composite exhibits ferroelectric and ferrimagnetic-like properties, revealing its multiferroic behavior. Furthermore, the impedance analysis of the composite shows the negative temperature coefficient of resistance behavior. The present study describes the structural and physical properties of the possible lead-free multiferroic composite. [ABSTRACT FROM AUTHOR]

• Sr doped LCMO double perovskite nanoparticles were synthesized using sol–gel method. • Nanoparticles were studied using XRD, TEM, FTIR, Raman, Uv–Vis and M−H curves. • Resistivity curve (R-T) suggest the semiconducting nature for the compound. • M−H and ZFC-FC curves show the interesting magnetic properties of Sr doped LCMO. A study on crystal structure and physical properties has been performed on nanoparticles of lead-free double perovskites, La 2 CoMnO 6 (LCMO) and Sr-doped La 2-x Sr x CoMnO 6 (LSMO:0 ≤ x ≤ 0.08) prepared by the sol–gel synthesis method. In preparation for the LSMO nanoparticle, the La site of the LCMO double perovskite was replaced with an increasing concentration of Sr atom. Structural investigation done by employing the X-ray Diffraction technique indicates that the crystallite size decreases as the doping concentration increases. The Rietveld refinement on the XRD pattern shows the formation of the rhombohedral phase of LCMO (S.G. no. 161). Strain in the prepared samples estimated from Williamson Hall (W-H) analysis shows that the strain decreases as crystallite size decreases. The presence of compressive strain is also evident from the blue shift obtained in the Raman spectrum of the nanoparticles. The UV–Vis spectra reveal the maximum absorption in the near UV region of the electromagnetic spectrum. The Bandgap analysis from Tauc's plot shows an increase in band gap with Sr doping in the LCMO host lattice (from 1.81 eV to 1.92 eV). This is attributed to the decrease in crystallite size and octahedral tilting with Sr doping. Resistivity versus temperature plots reveal the semiconducting nature of the compound. A linear nature graph between l n ρ and T - 1 4 indicates that the electric transport mechanism is governed by the variable range Hopping (VRH) model. The M−H curves show that the maximum magnetization decreases as a result of Sr doping due to the anti-site disorder introduced. dM/dT vs T curve shows two magnetic transitions at ∼ 215 K and at ∼ 173 K which are due to Co2+–O2--Mn4+ and Co3+–O2--Mn4+ ferromagnetic superexchange interactions, respectively. [ABSTRACT FROM AUTHOR]

In the present research work, a conventional solid-state synthesis approach was used to synthesize the polycrystalline compound of Mg-doped ZnO (Zn 1-x Mg x O with x = 0–0.12). The XRD analysis reveals that Mg-doped compounds have been crystallized in a single hexagonal phase. The SEM analysis revealed that these compounds are constituted with microscopic spherical particles with a size range of 1–3 μm. Raman scattering spectra of these compounds displayed a blue-shift of the Raman active E 2 (low) mode attributed to the vibration of zinc atom in wurtzite ZnO, indicating Mg ions were substituted successfully into the ZnO lattice. Optical measurements revealed that the optical band gap enhanced from 3.12 to 3.17 eV, while the transmittance value improved from 87% to 96% as the Mg doping percentage is increased. The magnetization (M) versus applied field (H) measurements, done at 300 K reveals that the undoped ZnO compound exhibits weak ferromagnetic behavior, whereas all Mg-doped ZnO compounds show a strong ferromagnetism with coercivity ranging between 85 O e ≤ H c ≤ 1482 O e , and with the highest saturation magnetization of 0.255 emu/gm for 12% Mg-doped sample. [ABSTRACT FROM AUTHOR]

This study explores the effects of filler concentrations of lanthanum-doped lead zirconate titanate (PLZT) on the electrical and mechanical characteristics of nanocomposite thick film. Crystal structure and morphology of the thick film have been studied using X-ray diffraction, atomic force microscopy, and scanning electron microscopy techniques. It has been noted that adding PLZT nanoparticles to the polyvinylidene fluoride (PVDF) matrix modifies the physical properties of PVDF. In the nanocomposite film, the most prominent polar β phase has been identified at 6 mol% of PLZT filler. In all the films, a nearly homogenous grain distribution has been observed. Frequency-dependent dielectric, conductivity, and impedance of the sample were studied at room temperature. Maximum electric dipole polarization of 0.68 μC/cm2 and piezoelectric (d33) constant of 48 pC/N have been observed at 6 mol% of PLZT filler in the PVDF matrix. Indeed, it has been observed that the (0.94)PVDF–(0.06)PLZT nanocomposite film is well suited for applications such as nanogenerators, structural health monitoring systems, and various kinds of sensors and actuators. [ABSTRACT FROM AUTHOR]

Temperature-dependent dynamic ferroelectric hysteresis of semiconductor–relaxor ferroelectric (0–3) type composite {0.30(ZnO)–0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBTO)]} has been investigated using polarization–electric field (P–E) loops, current density–electric field (J–E) curves, and temperature-dependent dielectric permittivity. It is well known that the polarization reversal mechanism can be explained by the concept of ferroelectric domain switching kinetics, which depends strongly on the temperature. The present work ascribes the role of polar nanoregion induced thermal depolarization field on the temperature-dependent ferroelectric hysteresis loop along with polarization reversal mechanism. The present composite exhibits unique ferroelectric switching behavior above the thermal depolarization temperature (∼100 °C), which is observed in P–E and J–E loops. The depolarization field-induced pinched P–E loops of a BNBTO solid solution above Td (∼100 °C) have been significantly overcome by the incorporation of semiconductor (ZnO) particles, which extensively described the underlying mechanism in the present context. In addition, the temperature-dependent polarization reversal mechanism displays unique two-stage processes [low-T (<100 °C) and high-T (>100 °C)] for the minor loops (∼30 and 40 kV) and saturated loops (∼45 kV) as described by the electric field–temperature phase diagram. The present results may provide a distinct way to Bi0.5Na0.5TiO3-based solid solutions for high-temperature piezoelectric applications. [ABSTRACT FROM AUTHOR]

In this study, the crystal structure and magnetic properties of two sets of multiferroic nanocomposites of Bi0.85La0.15FeO3 (BLFO) and BaTiO3 (BTO) were reported. The samples were prepared by adopting the conventional solid-state reaction and ball mill technique. The X-ray diffraction pattern and Raman spectra analysis reveal the impurity-free crystal structure, and both the phases (i.e., BLFO and BTO) are present in parallel in the nanocomposites. Scanning electron microscopy was used to study the surface morphology. The saturation magnetizations of the ball-milled nanocomposite are found to be significantly higher compared to that of the solid-state composites. The Vegard law was used to compare the observed saturation magnetization with the oretical values. The pinched hysteresis loop was observed in both sets of composites, which was explained by exchange type magnetic interaction between BLFO and BTO. The squareness ratio (R) tells the presence of intergrain magnetostatic interaction in the composites. The hysteresis loop width (ΔH) versus magnetization (M) plots for all the composites reveals the hysteresis loop anomalies. [ABSTRACT FROM AUTHOR]

The composites (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 are prepared by solid‐state reaction method using microwave double‐step sintering. Ba0.8Sr0.2TiO3 crystallizes to tetragonal crystal symmetry with P4mm space group and CoFe2O4 crystallizes to cubic crystal symmetry with Fd3¯m space group. Electron microscopy techniques are used to understand the microstructure, elemental composition, and morphology of the composites. The dielectric properties are measured in the 1 Hz–1 MHz frequency range and 40–400 °C temperature range. Composite with x = 0.1 (ε′ ≈ 170, tan δ = 0.08 at 1 kHz) and 0.2 (ε′ ≈ 390, tan δ = 0.07 at 1 kHz) has better dielectric properties than the parent Ba0.8Sr0.2TiO3 ferroelectric (ε′ ≈ 125, tan δ = 0.16 at 1 kHz) and CoFe2O4 ferrimagnetic phases (ε′ ≈ 375, tan δ = 0.72 at 1 kHz), respectively. Composite with 10% cobalt ferrite has the highest saturation polarization (2.1 μC cm−2), the highest remanent polarization (0.9 μC cm−2), and coercive field (23.9 kV cm−1) compared to ferroelectric phase followed by x = 0.2 composite (PS = 1.6 μC cm−2, Pr = 0.8 μC cm−2, and EC = 19.2 kV cm−1). Composite with x = 0.2 shows the highest magnetic coercive field of 1.96 kOe. Hence, this article advocates that 20% ferrite in the composites is the optimized composition for multiferroic applications. The present study will help to explore piezoelectric, magnetostrictive, and magnetoelectric properties of (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 for the technological application. [ABSTRACT FROM AUTHOR]

Incorporation of different types of nanofillers in the PVDF poly(vinylidene difluoride) matrix exhibits promising dielectric, magnetic, piezo, pyro, and ferroelectric properties for various applications. Hence a novel nanocomposite has been developed by using PVDF and cobalt ferrite (CFO) (CoFe2O4) with different particle size of CFO for dielectric applications. The nanocomposite has been characterized by the X‐ray diffraction pattern, atomic force microscopy, transmission electron microscopy, fourier transform infra‐red spectroscopy, field emission‐scanning electron microscopy), and dielectric measurements. The space charge effect at the PVDF and CFO interfaces offers the interfacial polarization in nanocomposite, which contribute to tune the dielectric response of nanocomposite along with low dielectric loss. The filler size has been optimized to have better formation of polar β phase in PVDF along with high dielectric properties. The dielectric constant in nanocomposite has increased three times compare to that of PVDF. The 20 ± 1 nm size (CFO) filler in PVDF matrix exhibits optimized dielectric properties. POLYM. COMPOS., 40:1239–1250, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this study, the tartaric acid modified sol–gel method was used to synthesize (1–x)Bi 0.85 La 0.15 FeO 3 -(x)CoFe 2 O 4 (BLFO-CFO) composites where x = 0.00, 0.10, 0.20, 0.30, 0.40, and 0.50. The X-ray diffraction (XRD) patterns indicated the formation of composites with both BLFO and CFO crystal symmetry, i.e., perovskite and spinel structures, respectively. Rietveld refinement of the XRD patterns was performed for all of the samples in order to analyze the crystal phases and obtain the structural parameters. There were decreases in the lattice parameters of the perovskite phase as the CFO spinel phase increased in the composites, which may be explained by the strain at the interface of the BLFO and CFO phases. Electrical polarization and dielectric constant enhancements were observed in the BLFO-CFO composites compared with BLFO. The saturation magnetization increased as the CFO phase increased in the composites. The theoretical saturation magnetization (calculated using Vegard's law) was less than the experimentally observed value, possibly due to the spin interaction at the interface of BLFO and CFO. [ABSTRACT FROM AUTHOR]

The polymer nanocomposites have potential applications in flexible electronics due to its interesting dielectric properties. Hence, flexible nanocomposite films of polyvinylidene fluoride (PVDF) polymer and barium hexaferrite (BHF) nanoparticles with high dielectric constant were prepared by the solution cast method. The dielectric behavior of the materials has been understood by employing the impedance spectroscopy technique. The co-existence of α and β phases of PVDF has been observed from the XRD (X-ray Diffractometer) and FTIR (Fourier-transform infrared spectroscopy) analysis. The ratio of α and β phases of PVDF has a great influence on dielectric, ferroelectric and energy storage density of PVDF-BHF nanocomposites and, it depends upon the concentration of BHF in the nanocomposites. FE-SEM (Field Emission Scanning Electron Microscopy) micrographs reveal that the microstructure of the composite depends upon the concentration of BHF in the PVDF matrix. Dielectric properties of nanocomposite highly depends on microstructure of the PVDF-BHF nanocomposite. This observation has been well explained by considering the BLCs (Barrier Layer capacitances) model. Interestingly, the dielectric constant has been enhanced eighteen (18) times at 1 KHz to that of dielectric constant of PVDF. The dielectric constant increases due to the electrostatics and interfacial interaction between the local electric field of the BHF nanoparticle and CH2/CF2 dipole of PVDF chain. The present study opens a new window for the possible use of PVDF-BHF nanocomposite in dielectric and energy storage device applications. [ABSTRACT FROM AUTHOR]

Nanocomposite of NiO and CoFe 2 O 4 (CFO) has been prepared using the high energy planetary ball mill technique. Both crystallographic symmetries correspond to NiO and CFO has been observed from the X-ray diffraction pattern, which indicates no major chemical reaction between the two phases. The fraction of weight percentage for CFO and NiO are obtained from the double phase Rietveld analysis by using the space group F d 3 ¯ m for CFO and F m 3 ¯ m for NiO and, it is found to be as per the expected one. Magnetocrystalline anisotropy has been studied by analyzing magnetic hysteresis loop (obtained in the field range of ±2T) by employing the Law of approach to saturation. The anomaly in the hysteresis loops at symmetric position in the nanocomposite reveals the interaction between antiferromagnetic (NiO) and ferrimagnetic (CFO) phases at the interface. [ABSTRACT FROM AUTHOR]

Multiferroic composites are the current research interest due to their multi-functional behavior with promising electrical and magnetic properties compared to single crystallographic phase multiferroic materials. Hence, multiferroic composites of (1−x)Bi0.85La0.15FeO3-(x)NiFe2O4 (x = 0 to 0.50) have been investigated by considering Bi0.85La0.15FeO3 as a ferroelectric phase and NiFe2O4 as a magnetic phase. The crystal structure was examined by analyzing the X-ray diffraction (XRD) patterns. Different crystal structure parameters were obtained from the Rietveld refinement of XRD patterns. An increase in the lattice parameters of both Bi0.85La0.15FeO3 (BLFO) and NiFe2O4 (NFO) phases has been observed with the increase in the percentage of NiFe2O4 in the composites. Absorption peaks in Raman spectra shift toward lower frequencies with the increase in the percentage of NFO in the composite. Variation of lattice parameters and shifting of the Raman modes suggest the lattice strain at the interfaces of BLFO and NFO. Theoretical magnetizations were calculated for all composites by using the sum rule (using the magnetization of individual phases) and compared with experimentally observed magnetization. Interestingly, the experimental values of magnetizations of the composites are more than the theoretically calculated ones. It could be due to the lattice strain, which was observed from the XRD and Raman analysis. [ABSTRACT FROM AUTHOR]

The analysis of structural, electrical transport, critical magnetic behavior, and magnetocaloric properties of Co2CrAl Heusler alloys has been conducted here. Co2CrAl full Heusler alloy has been prepared by the conventional arc melting method in Ar atmosphere and post‐annealing in a vacuum‐sealed quartz tube. X‐ray diffraction (XRD) pattern reveals the crystallization of the alloy to the Fm3¯m space group with L21 crystal symmetry. The correspondence between the magnetic and electrical transport properties of the Co2CrAl alloy has been observed. This alloy exhibits paramagnetic to ferromagnetic transition (Curie temperature) just above room temperature at around 340 K. Metallic to semiconducting transition occurs near the magnetic Curie temperature. Critical magnetic behavior has been analyzed by employing the Arrott plot, Kouvel–Fisher methods, and critical isotherm analysis. These conclude that the exchange interaction in Co2CrAl alloy follows between mean‐field theory having spin–spin long‐range interaction and the 3D Heisenberg model. The magnetocaloric effect has been explored from the isothermal magnetization data by employing Maxwell's equations. The highest magnetic entropy change is found to be ≈0.99 J (kg K)−1 for a magnetic field change of 30 kOe. A large working temperature window of 57 K is the advantage of the present alloy. [ABSTRACT FROM AUTHOR]

An attempt has been made here to synthesized ceria (CeO2) and Ce0.80Zr0.20−xAxO2 (A = Fe, Co; x = 0–0.20) powders via novel sol–gel technique using metal nitrate hydrates as precursors and distilled water and ethanol as solvents. The resulting gel was dried at 130 °C for 24 h and calcined successively at 850 and 950 °C for 3 h each. Ceria is shown to exhibit a fluorite-type cubic structure with a slightly higher lattice parameter a = 5.428 Å, Z = 4, space group Fm 3 ¯ m , some Ce3+ ions and oxygen vacancies. 20% zirconium substitution of cerium causes decrease of ‘a’ to 5.395 Å owing to a lower ionic radius of Zr4+ vis-à-vis Ce4+. However, the lattice parameter first increases and then decreases with partial/ full replacement of Zr4+ by cobalt or iron ions. Evidence is found for existence disorder/strain, mismatch of ionic radii and oxidation states of cations, and appropriate oxygen vacancies to ensure charge neutrality of systems. The photoluminescence (PL) spectra reveal peaks at ~ 371, 402, and 432–445 nm, which are attributed to Ce 4f0 → 4f1 direct transition, Ce 4f0 → 4f1 electron transfer via oxygen F++ state, and oxygen vacancies (excited oxygen F+* → F+ transition), respectively. Their Raman spectra display a peak at ~ 462 cm−1 due to F2g symmetric vibrations of a cubic CeO8 sub-cell with some variation in position and sharpness with/without a signal in the range 150–170 cm−1 by introduction of different cations leading to distortion and formation of anion vacancies. [ABSTRACT FROM AUTHOR]

The magnetic properties of nanocrystalline cobalt ferrite could be tuned with substituting small amount of non-magnetic rare earth cation at Fe site in cobalt ferrite. The variation in magnetic parameter of samples could also be obtained by measuring its anhysteretic magnetization curve without tailoring its chemical composition. The magnetic parameters such as coercivity, remanent magnetization and saturation magnetization critically depend upon different values of external magnetic fields. In the present study, the anhysteretic magnetization curve of the samples CoFe2-xLaxO4 (x=0.025, 0.05, 0.075 and 0.1) has been recorded and response of coercivity to different maximum values of applied field has been investigated. It has been observed that the response of coercivity to different maximum values of applied field shows non-linear behavior. The analysis of the response of coercivity to different values of applied field in low field regime has been carried out with the help of Rayleigh laws. The analysis of the plot yields significant information about magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Ferroelectric perovskites materials are the most promising materials because of their multifunctional applications as well as the ongoing fundamental research on them. The present study investigates the correlation between the crystal structure and various physical properties such as dielectric, ferroelectric, and optical properties of Sr2+ modified Sodium bismuth titanate Na 0.5 Bi 0.5−x Sr x TiO 3 (x = 0.00, 0.02, 0.04, and 0.06) synthesized by solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern reveals that the system undergoes a crystal symmetry transition from a two-phase crystal symmetries system (rhombohedral (R3c) and tetragonal (P4bm)) to a three-phase crystal symmetries system (rhombohedral (R3c), tetragonal (P4bm) and Cubic (Pm 3 ̅ m)) with the rise in Sr2+ concentration in Na 0.5 Bi 0.5−x Sr x TiO 3 which is the foremost reason behind the variation of physical properties of the system. The dielectric constant and maximum polarization increase with the Sr2+ concentration up to 2% and it decreases with the further increase in Sr concentration due to the distortion in crystal structure induced by the introduction of cubic phase (Paraelectric) in the system. The maximum value of the dielectric constant is estimated to be 3629 at a low frequency on the Na 0.50 Bi 0.48 Sr 0.02 TiO 3 system. The optical band gap (E g) of Na 0.5 Bi 0.5−x Sr x TiO 3 (x = 0.00, 0.02, 0.04, and 0.06) ceramics are found to vary between 3.202 eV to 3.172 eV which indicates the semiconducting nature of prepared samples but urbach energy shows an opposite behaviour i.e. increases with Sr concentration. [Display omitted] • Crystal symmetry transition occurs from R3c + P4bm to R3c + P4bm + Pm 3 ̅ m. • Na 0.50 Bi 0.48 Sr 0.02 TiO 3 exhibits Maximum polarization of 7.05 μC/cm2. • The highest dielectric constant is found to be 3629 for Na 0.50 Bi 0.48 Sr 0.02 TiO 3. • Na 0.50 Bi 0.48 Sr 0.02 TiO 3 ceramics exhibits a low optical band gap of 3.138 eV. • Sr2+ modified NBT can be utilized in various technological applications. [ABSTRACT FROM AUTHOR]

• Overall magnetic properties depend on phase evolution. • Average particle size increased with increasing annealing temperature. • Transition from single-domain to multi-domain configuration with annealing. • Incoherent magnetization reversal mechanism in single domain Ba 1-x Sr x Fe 12 O 19. The correlation of phase evolution (annealing at different temperatures) with magnetic properties like magnetization reversal, coercivity mechanism, and energy product in M-type hexaferrite by substituting Sr in place of Ba has been reported in the present article. The Ba 1-x Sr x Fe 12 O 19 (x = 0.0, 0.5, & 1.0) have been prepared by the sol–gel auto-combustion method followed by annealing at different temperatures from 800 °C to 1200 °C. The structural and magnetic properties have been characterized by X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy, and Vibrating sample magnetometer. The Rietveld refinement confirms contraction in unit cell parameters by replacing Sr in place of Ba and lattice expansion with increasing annealing temperature. There is no significant effect of substitution on magnetic properties found rather heat treatment affects greatly. The transition from a single domain to multidomain particles and their contribution to initial magnetization curves are analyzed. The differential susceptibility (dM/dH) calculated from room temperature magnetization confirms the existence of a pinning effect during magnetization reversal for samples heat treated below 1200 °C. Secondary phases or grain boundaries are believed to act like pinning centers. This work opens insight into the domain wall motion by microstructure engineering. The coercivity is tuned to 6.09 kOe by controlling the annealing temperature for the Ba 1-x Sr x Fe 12 O 19 (x = 1.0) sample. The maximum energy product (BH) max in the range of 0.94–1.27 MGOe has been achieved. [ABSTRACT FROM AUTHOR]

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe 1.97 RE 0.03 O 4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO 3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe 1.97 La 0.03 O 4 and, 20% and 80% for NiFe 1.97 Sm 0.03 O 4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (M s) and magneto-crystalline anisotropy constant (K 1) estimated from the "Law of Approach to Saturation" equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch's law and Kneller's relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe 1.97 La 0.03 O 4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe 1.97 Sm 0.03 O 4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher's power law suggests that the charge carrier's conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe 1.97 La 0.03 O 4 and NiFe 1.97 Sm 0.03 O 4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe 1.97 Sm 0.03 O 4 than that of the La3+ substituted sample. [Display omitted] • Samples crystallized to single phase cubic spinel structure with F d 3 − m space group. • ZFC-FC analysis reveals intermediate type magnetic interaction between particles. • SAR is estimated by initial slope, Box-Lucas and modified Newton cooling approach. • Nyquist plots reveal non-Debye type dielectric relaxation and NTCR type behavior. • Presence of considerable induced dipole-dipole interaction in current samples. [ABSTRACT FROM AUTHOR]