Magnetoelectric and dielectric properties of Ni0.5Cu0.5Fe2O4–Ba0.5Pb0.5Ti0.5Zr0.5O3 ME composites

The (x) Ni_0.5Cu_0.5Fe₂O₄ + (1−x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ ME composites have been synthesized by a standard ceramic method. The presence of single phase in x = 0 and x = 1 as well as two phases in x = 0.15, 0.30 and 0.45 composites has been confirmed by XRD. The dielectric constant (ε′) and dielectric loss (tan δ) have been studied as a function of temperature and frequency. These composite materials exhibit maximum dielectric constant with a variation of frequency and temperature. The composite 15% Ni_0.5Cu_0.5Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ had the highest magnetoelectric voltage coefficient of 0.248 mV/cm Oe at room temperature among the studied composites.     

Dielectric and magnetoelectric properties of (Ni,Cu)Fe2O4 + [(Ba,Pb)(Ti,Zr)]O3 composites

The observation of magnetoelectric coupling is reported in (x) Ni_0.8Cu_0.2Fe₂O₄ + (1 − x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ composites synthesized by normal solid state reaction method. The phase formation was confirmed by X-ray diffraction technique and no intermediate or impurity phase is present in all the composites. The dielectric constant (ε′) and dielectric loss (tan δ) were measured as a function of frequency and temperature. The dielectric constant was found to be enhanced with increase in ferrite content in the composite. It was also revealed that magnetoelectric output decreases with increase in ferrite content in the composite due to leakage current. The maximum voltage coefficient of 0.411 mV/cm/Oe was observed in 15% Ni_0.8Cu_0.2Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ composite.     

Effect of piezoelectric grain size on magnetoelectric coefficient of Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 particulate composites

This study investigates the variation of magnetoelectric (ME) coefficient as a function of the piezoelectric grain size in the composite system of 0.8 Pb(Zr_0.52Ti_0.48)O₃–0.2 Ni_0.8Zn_0.2Fe₂O₄. It was found that as the piezoelectric-phase grain size increases the overall resistivity, piezoelectric, dielectric, and ferroelectric property of the composite increases and saturates above 600 nm. Below 200 nm average grain size, piezoelectric and dielectric properties decrease rapidly. The ferroelectric Curie temperature was found to decrease from 377 to 356 °C as the average grain size decreases from 830 to 111 nm. ME coefficient of the composite showed a rapid change below grain size of 200 nm and was found to saturate above 600 nm to a value of 155 mV/cm.Oe.     

Dielectric behaviour and magnetoelectric effect in Ni0.5Co0.5Fe2O4+Ba0.8Pb0.2TiO3 ME composites

Magnetoelectric composites with compositions xBa_0.8Pb_0.2TiO₃+(1−x)Ni_0.5Co_0.5Fe₂O₄ in which x varies as 0, 0.55, 0.70, 0.85 and 1.0 were prepared by double sintering method. The presence of single phase in x=0 and x=1 as well as two phases in x=0.55, 0.70 and 0.85 composites has been confirmed by XRD. The dielectric constant and loss tangent were studied as a function of frequency and temperature. The static value of the magnetoelectric conversion factor, i.e. d.c. (ME)_H was studied as a function of the magnetic field. The maximum value of ME coefficient was observed for x=0.85 composite, whereas minimum for x=0.55 composite.     

Ba(Zn1/3Nb2/3)O3/Ni0.8Zn0.2Fe2O4 magneto-dielectric composite with large dielectric constant and high permeability

Ba(Zn_1/3Nb_2/3)O₃/Ni_0.8Zn_0.2Fe₂O₄ (BZN/NZO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using XRD and SEM, respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BZN/NZO composites have large dielectric constants and very high permeabilities. For the 20%BZN/80%NZO composite, the dielectric constant and permeability in low frequency range are about 8,000 and 18, respectively. The large dielectric behavior of the BZN/NZO composites is mainly attributed to the Maxwell–Wagner polarization.     

Piezoelectric and magnetic properties of PZT-(Ni<Subscript>0.284</Subscript>Zn<Subscript>0.549</Subscript>Cu<Subscript>0.183</Subscript>)Fe<Subscript>1.984</Subscript>O<Subscript>4</Subscript> composites

The piezoelectric/piezomagnetic composite, PZT/Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄, was fabricated by the mixed oxide method. The phase assemblage, piezoelectric strain constant and saturation magnetization were investigated. The results indicate that the PZT phase is compatible with Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄ phase, and dense diphasic ceramic composites were obtained. It is found that piezoelectric strain constant decreases exponentially as the amount of doped piezomagnetic materials in the composite increases. Correspondingly, saturation magnetization of the composite also decreases with the increasing weight fraction of piezoelectric materials. Three reasons cause the results. First, the grain growth of piezomagnetic phase at the co-sintering temperature reduces grain size and continuity of the piezoelectric phase. Second, the pore size and porosity in composite increase dramatically with increasing amount of piezomagnetic phase. Third, the low resistivity of the composite prevents the poling process and reduces the piezoelectric strain constant. The tailoring of microstructure to achieve a high performance piezoelectric/piezomagnetic composite is proposed based on the analysis.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Electrical conduction, dielectric behavior and magnetoelectric effect in (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 ME composites

Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO₃ + (1 − x)Ni_0.94Co_0.01Mn_0.05Fe₂O₄ where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)_H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase.     

Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of Ni_xCo₁–_xFe₂O₄, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (T_c) for all samples was noted from resistivity data. The activation energy below and above T_c was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline Ni_xCo₁–_xFe₂O₄ at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples.     

Structural and Electrical Properties of Ni-Co Nanoferrites Prepared by Co-precipitation Route

A series of Ni_1?x Co _x Fe₂O₄ (x=0.1, 0.2, 0.3, 0.4, 0.5) spinel ferrites have been synthesized successfully using the chemical co-precipitation route. The materials were characterized by X-rays powder diffractometry (XRD) and the electrical properties. The obtained crystallite size variation was within 15 to 33 nm using the Scherrer formula. The dc electrical resistivity was measured as a function of temperature. It is noticed that ?? _dc increases with a rise in temperature. The dielectric measurements were carried out at room temperature as a function of frequency and composition (x). The dielectric constant (????) and dielectric loss tangent (tan???) showed a decreasing trend with increasing field frequency. The ac electrical conductivity is calculated from the dielectric measurements; it increases with the rise in frequency.     

Studies on electrical properties of ( x ) BaTiO3?+?(1? x ) Ni0.92Co0.03Mn0.05Fe2O4 ME composites

The (1−x) Ni_0.92Co_0.03Mn_0.05Fe₂O₄ + (x) BaTiO₃ magnetoelectric (ME) composite have been prepared using conventional double sintering ceramic process where x varies as 1.00, 0.85, 0.70, 0.55 and 0.00. The presence of both phases has been confirmed by X-ray diffraction and the microstructure study will be carried out by SEM technique. The dc resistivity and thermo-emf of the samples have been studied with variation in temperature. The variation of dielectric constant (έ) and loss tangent (tan δ) will be measured in the frequency range 100 Hz–1 MHz. The ac conductivity has been derived from dielectric constant (έ) and loss tangent (tan δ). The static value of magnetoelectric conversion factor dc (ME)_H has been studied as a function of intensity of magnetic field.     

Magnetic and dielectric properties of Ni0.8Zn0.2Fe2O4/HDPE composites for high-frequency application

A low loss high-frequency magnetic composite with Ni_0.8Zn_0.2Fe₂O₄ (NZO) ultrafine particles embedded in a high density polyethylene (HDPE) matrix was fabricated by using a simple low-temperature hot-pressing technique. The magnetic and dielectric properties of the as-prepared composites were investigated in details. The results indicate that as the volume of the ceramic fillers increase, the permittivity, permeability, dielectric and magnetic loss of the composite all increase. The cut-off frequencies of the composites are all above 1 GHz. Because of the low resistivity of NZO, the dielectric losses of the composites are big and decrease with frequency below 100 MHz. Good frequency stabilities of the permittivities and permeabilities, and low dielectric and magnetic losses within the measurement range have been observed. For the composite containing 30 vol% NZO, the permittivity, dielectric loss, permeability and magnetic loss are 3.7, 0.0025, 2.2 and 0.002 at 100 MHz, respectively.     

Dielectric behaviour and a.c. conductivity in Cu x Fe3−x O4 ferrite

The dielectric properties (dielectric constant and loss) for the system Cu _x Fe_3−x O₄ with x = 1.0, 0.8, 0.6, 0.4 and 0.2, were studied in the temperature range 300 ∼ 800 K and also in the frequency range 1 kHz ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Magnetic properties and magnetoelectric effect in Ni0.8Co0.1Cu0.1Fe2O4 + PbZr0.2Ti0.8O3 composites

Composites with compositions x (Ni_0.8Co_0.1Cu_0.1Fe₂O₄) + (1−x) PbZr_0.2Ti_0.8O₃ (x-mole fraction varies as 0.15, 0.25, 0.35 and 0.45) were prepared by standard ceramic method. The presence of constituent phases, namely ferrite and the ferroelectric were confirmed by X-ray diffraction. The structural analyses were carried out using the obtained powder pattern X-ray data. The porosity of the samples was calculated and the values obtained lie between 10% to 19%. To date, the variations in the magnetic properties with variation in ferrite phase in composites and thereby its influence on magnetoelectric effect is not yet reported. The saturation magnetization (Ms) and magnetic moment (η_B) in Bohr magneton were calculated for all the composites. The static value of magnetoelectric voltage coefficient (dE/dH) was measured as a function of intensity of magnetic field. The maximum value of ME coefficient was observed for a composite with 35% ferrite + 65% ferroelectric phase.     

Composition dependent phase connectivity, dielectric and magnetoelectric properties of magnetoelectric composites with Pb(Mg1/3Nb2/3)0.67Ti0.33O3 as piezoelectric phase

Ferrite (Ni_0.6Co_0.4Fe₂O₄) phase, ferroelectric (Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃) phase and magnetoelectric composites of (x)Ni_0.6Co_0.4Fe₂O₄ + (1 − x)Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x = 0.15, 0.30 and 0.45 were prepared using solid-state reaction technique. Presence of Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ was confirmed using X-ray diffraction technique. The scanning electron microscopic images were used to study the microstructure of the composites. Connectivity scheme present in the magnetoelectric (ME) composites are discussed from the microscopic images. Variation of dielectric constant and dielectric loss with temperature for all the composites was studied. Here we report the effect of Ni_0.6Co_0.4Fe₂O₄ mole fraction on connectivity schemes between Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composite. The variation of magnetoelectric voltage coefficient with dc magnetic field shows peak behaviour. The maximum value of magnetoelectric voltage coefficient of 9.47 mV/cm Oe was obtained for 0.15Ni_0.6Co_0.4Fe₂O₄ + 0.85Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composites. Finally we have co-related the effect of Ni_0.6Co_0.4Fe₂O₄ content and dielectric properties on magnetoelectric voltage coefficient.     

Electrical properties of thick-film NTC thermistor composed of Ni0.8Co0.2Mn2O4 ceramic: Effect of inorganic oxide binder

The thick-film NTC thermistors were prepared by screen printing Ni_0.8Co_0.2Mn₂O₄ ceramic on the alumina. The influence of inorganic oxide binder composition and thickness of thermistor layer on the thermistor constant and initial resistivity are studied. The relation between the resistivity (ρ) and the absolute temperature for the prepared thick-film thermistor comply with Arrhenius equation. The room temperature sheet resistivities of the thick films were in the range 0.56-7.45 MΩ cm and temperature sensitivity index in the range 1492-3335 K. Binder composition dependent agglomeration of microcrystallites is observed in the microstructure of the thick-film Ni_0.8Co_0.2Mn₂O₄ ceramic. The spinel ceramic was prepared by oxalate co-precipitation and sintering.     

Dispersion of dielectric constant and resistivity of Cu x Zn1−x Fe2O4 samples

Cu _x Zn_1−x Fe₂O₄ samples exhibit dispersion of dielectric constant, tanδ and resistivity in the frequency range of 1 kHz to 50 MHz. The dispersion exhibited is in general accord with Koops’ model. However, the details of the conducting and non-conducting regions must be taken into account when composition tends to change interrelationship between the elementary capacitor resistor circuits. On quenching these samples from 800°C the dielectric constantε ¹ showed an increase for CuFe₂O₄ and Cu_0·8Zn_0·2Fe₂O₄ samples. The dielectric constant of the remaining samples showed no influence on quenching. The compositional variation showed that the dielectric constant has higher value for the ferrite Cu_0·4Zn_0·6Fe₂O₄ The results are explained on the basis of cation transfer.     

Studies on dielectric and magnetoelectric behavior of 25% CMFO ferrite and 75% BZT ferroelectric multiferroic magnetoelectric composites

In the present work, multiferroic magnetoelectric (ME) composites of ferrite and ferroelectric phases are prepared. Here, the magnetostrictive (ferrite) phase, Co_1.2 − yMn_yFe_1.8O₄ (y = 0.0 to 0.4) i.e. CMFO is synthesized by chemical combustion route and the piezoelectric (ferroelectric) phase, BaZr_0.08Ti_0.92O₃ i.e. BZT is synthesized by conventional ceramic method. Frequency dependent dielectric constant measurement from 20 Hz-1 MHz at room temperature shows usual dielectric dispersion behaviour, which may be attributed to the Maxwell-Wagner type interfacial polarization. Temperature dependent dielectric constant measurement shows two dielectric maxima, one below 100 °C and the second above 500 °C. The dielectric maxima below 100 °C corresponds to the transition temperature of the ferroelectric phase and that of above 500 °C corresponds to the transition temperature of the ferrite phase of the ME composites. It is observed that as Mn content increases in the cobalt ferrite, the phase transition temperature of the ferrite phase decreases. The static magnetoelectric voltage coefficient was measured as a function of intensity of the applied dc magnetic field. These magnetoelectric composites may have possible applications in magnetic field sensing probes and linear ME devices.