The role of Mg substitution on the microstructure and magnetic properties of Ba Co Zn W-type hexagonal ferrites

A series of W-type hexagonal ferrites with the composition BaCoZn_1−xMg_xFe₁₆O₂₇ (0?x?0.6) were prepared by the conventional ceramic method to study their structural and magnetic properties as a function of temperature and composition. The characterization using X-ray diffraction indicated that a hexagonal W-type single-phase structure and the effect of composition on the unit cell parameters, density and porosity was studied. The variation of the magnetic susceptibility (χ_M) with temperature for all the investigated samples in the temperature range (300–800 K) shows three regions of behavior that was explained on the basis of the distribution of Zn²⁺ and Mg²⁺ ions in the lattice and leads to the anomalous behavior of the effective magnetic moment μ_eff. The Curie temperature indicated that the critical concentration is at x=0.5. Paramagnetic nature of the samples above the Curie temperature is observed. The Curie Weiss constant θ calculated from the plot of 1/χ_M vs. T (K) is in agreement with the expected value. The effective magnetic moment μ_eff decreases with increasing the intensity of magnetic field. The possible mechanisms contributing to these properties are discussed in the text.     

Effect of magnesium substitution on dielectric and magnetic properties of Ni-Zn ferrite

The dielectric and magnetic properties of Mg incorporated Ni-Zn spinel ferrites have been investigated. Ni_0.5−xZn_0.5Mg_xFe₂O₄ ferrites have been prepared by sol-gel auto-combustion technique. The as prepared ferrites were annealed at 673, 873 and 1073 K. The X-ray diffraction studies reveal the spinel structure of annealed ferrites. The TEM results are in agreement with XRD results. FTIR study has also been carried out to get insight into the structure of these ferrites. The dielectric measurements show that the dielectric constant (ε′), dielectric loss (tan δ) and conductivity (σ_ac) increase on incorporation of Mg in the Ni-Zn ferrite. ε′, tan δ and σ_ac also show dependence on temperature, frequency of external applied electric field and microstructure of the samples. The magnetic moment measurements reveal that the saturation magnetization (M_s) increases and coercivity (H_c) decreases with the increase in concentration of Mg²⁺ ions. M_s and H_c also show dependence on the annealing temperature.     

Physical properties of BaMg1/3Nb2/3O3-BaCo1/3Nb2/3O3 solid solutions

Structural, electric and magnetic properties of Ba₃Mg_1−xCo_xNb₂O₉ based dielectric ceramic compounds have been studied. The samples, prepared by a solid state reaction method, were characterised by X-ray powder diffraction (XRPD), electron microscopy (SEM), dielectric (ε(T)) and magnetic measurements (χ⁻¹(T)). The XRPD analyses showed that the crystal structure of these compounds does change by the increase of substitution degree, passing from a superstructure hexagonal-type, (no. 164), space group (SG) to a simple structure cubic-type, (no. 221), SG. However, the evolution of the elementary unit cell lattice parameter can be followed and it exhibit a linear increasing tendency with increase in the substitution, indicating the existence of a solid solution through out the investigated range of substitution (0-1). The microstructure analysis shows a variation in the grain size and also the porosity of the samples with the degree of substitution. The results are in good agreement with that of dielectric measurements, which also showed that the dielectric constant (ε) increases with the increase of cobalt content. The magnetic characterization of cobalt substituted samples showed an antiferromagnetic type super-exchange interaction between these magnetic ions. At the same time, the values of effective magnetic momentum (μ_eff) are close to the value that corresponds to Co²⁺ free ions. The study highlights the possibility of modelling these materials by substitutions, in order to improve properties of negative-positive-zero (NPO) type dielectric applications.     

Structure, electric and dielectric studies of indium-substituted magnesium copper manganese ferrites

The structure, electric and dielectric properties of In-substituted Mg-Cu-Mn ferrites having the general formula of Mg_0.9Cu_0.1Mn_0.1In_xFe_1.9−xO₄ with 0.0≤x≤0.4 have been studied. X-ray diffraction (XRD) patterns of the samples indicated the formation of single-phase cubic spinel structure up to 0.2 and mixed phase (cubic and tetragonal phase) for samples x≥0.3. The relation of conductivity with temperature revealed a semiconductor to semimetal behavior as In⁺³ concentration increases. Variation in the universal exponent s with temperature indicates the presence of two hopping conduction mechanisms: the correlated barrier hopping (CHB) at low In⁺³ content x≤0.1 and small-polaron (SP) hopping at In⁺³ content x≥0.2. The variation in dielectric permittivity (ε′, ε″) with temperature at different frequencies shows a normal behavior for the studied compounds, while the variation in dielectric loss tangent with frequency at different temperatures shows abnormal behavior with more than relaxation peak. The conduction mechanism used in the present study has been discussed in the light of electron exchange between Fe³⁺ and Fe²⁺ ions and hole hopping between Mn²⁺ and Mn³⁺ ions at the octahedral B-sites.     

X-ray diffraction and Mössbauer Studies of γ′-(Fe1−xSnx)4N compounds (0.0⩽x⩽0.3)

The structure and magnetic properties of γ′-(Fe_1−xSn_x)₄N samples have been studied using X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy. It has been shown that the single-phase (Fe_1−xSn_x)₄N compounds can be prepared in the composition range of 0.0⩽x⩽0.3, which have the similar structure as γ′-Fe₄N The lattice parameter with the increase of Sn concentration can be well fitted with two linear relationships a₀(x)=3.795+0.019x (with x⩽0.10 ) and a₀(x)=3.797+0.228(x−0.10) (with 0.1⩽x⩽ 0.3). The fitting results of Mössbauer spectra indicate that the hyperfine parameters have the same changing tendency with lattice parameter, and the Sn atoms have a preference to be located at the corner site.     

Magnetic properties of intercalation compounds MxTiS2 (M = 3d transition metal)

Magnetization measurements have been made on 3d transition-metal intercalation compounds of M_xTiS₂ (M = V, Cr, Mn, Fe, Co and Ni; 0 ⩽ x ⩽ 1) at 4.2, 77 and 300 K in static fields up to 20 kOe and in pulsed fields up to 160 kOe. The ac magnetic susceptibility measurements in dc fields have also been made for Fe_xTiS₂. We have identified various types of magnetic phases in M_xTiS₂, such as paramagnetic, spin-glass, cluster-glass or mictomagnetic, and ferromagnetic ones, depending on the kind of guest 3d metals and their concentrations. Magnetic properties of these materials can be understood in terms of an itinerant or band picture rather than a localized or rigid band model.     

Variation of the magnetic inhomogeneity in glassy FexNi80-xB18Si2 alloys

A careful analysis of the magnetization measurements of amorphous Fe_xNi_80-xB₁₈Si₂ alloys (3 ⩽ x ⩽ 15) above the percolation threshold (x_c = 2.55) has been performed. The non-monotonic variation of the effective critical exponent of the initial magnetic susceptibility, γ¹, with temperature is found to become less pronounced with increasing x - x_c, and probably disappears around x = 20. The tendency towards a homogeneous ferromagnetism around that concentration is also obtained from the analysis of the Arrott-Belov-Kouvel plots. The results are compared with those for similar glassy ferromagnetic systems and a possible origin of the magnetic inhomogeneity is discussed.     

Low-temperature preparation and properties of ceramics with composition (1−x)CaTiO3−xPbF2−xLiF

Fluorinated ceramics with initial composition (1−x)CaTiO₃+xPbF₂+xLiF were sintered at 950 °C. The X-ray diffraction (XRD) patterns of the samples showed the formation of a novel solid solution in the initial composition range 0⩽x⩽0.125. SEM observations were performed on fractured ceramics and DSC analyses were carried out from room temperature up to 600 °C. Three second-order phase transitions were detected for all the samples. Capacitors were prepared from the pre-sintered ceramics then dielectric measurements were performed as a function of temperature in the frequency range 10²–4×10⁷ Hz. The ε′_r−T curves exhibit the profile of dielectrics for class I capacitors, however the values of tan δ are too high (tan δ⩾1%).     

Magnetic and dielectric properties of low vanadium doped nickel-zinc-copper ferrites

The new spinel-type of general formula Ni_0.6+xZn_0.2Cu_0.2V_xFe_2−2xO₄ with 0.0≤x≤0.25 was synthesized by the usual ceramic method. Structure of the prepared ferrites was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Room temperature magnetic hysteresis loops were measured using magnetic field strength up to 6 kOe. Saturation magnetization (M_s) increased with vanadium content up to x=0.05 and then decreased. Variation of (M_s) as a function of x is explained in terms of cation redistribution between A and B sublattices. Coercive force (H_c), remanent induction (B_r) and squareness of the hysteresis loop (B_r/M_s) as functions of x are presented. Dielectric permittivity (ε′, ε″) and dielectric loss tangent (tan δ) were measured as functions of frequency and temperature. These parameters were found to be strongly dependent on V₂O₅ concentration. The variation of dielectric loss tangent with frequency at different temperatures shows abnormal behavior, where more than one relaxation peaks were observed at low and high temperatures. This behavior could be attributed to the collective contribution of two types of carriers (p and n) to polarization.     

Magnetic properties of the mixed spinel Mg1+xMnxFe2-2xO4

The structural and magnetic properties of the mixed spinel Mg_1+xMn_xFe_2-2xO₄ system for 0.1<= x <= 0.9 have been studied by means of X-ray diffraction, magnetization, a.c. susceptibility and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Mn⁴⁺ ions occupy only octahedral (B) sites replacing Fe³⁺ ions and the added Mg²⁺ ions substitute for A-site Fe³⁺ ions. All samples are magnetic at 12 K displaying Mössbauer spectra that have magnetic sextets coexisting with a central doublet that increases in population with increasing Mn concentration, indicating the presence of short range ordering (clustering). The Mössbauer intensity data show that Mn possesses a preference for the B-site of the spinel over the whole range of concentration. As expected, the hyperfine field and Curie temperature determined from a.c.susceptibility data decrease with increasing Mn content. Magnetization results indicate that on increasing dilution x, the collinear ferrimagnetic phase breaks down at x = 0.3 before reaching the ferrimagnetic percolation limit (x=0.6), as a result of the presence of competing exchange interactions, which is well supported by Mössbauer results. From all the above results, it is proposed that with increasing Mn content from x=0.6 to 0.9, the frustration and disorder increase in the system suppressing the ferrimagnetic ordering, and the system approaches to a cluster spin glass type of ordering at x=0.8 as reflected in the a.c.susceptibility and Mössbauer spectrum.     

Study on ionic conductivity and dielectric properties of PEO-based solid nanocomposite polymer electrolytes

The ionic conductivity and dielectric properties of the solid nanocomposite polymer electrolytes formed by dispersing a low particle-sized TiO₂ ceramic filler in a poly (ethylene oxide) (PEO)-AgNO₃ matrix are presented and discussed. The solid nanocomposite polymer electrolytes are prepared by hot press method. The optimum conducting solid polymer electrolyte of polymer PEO and salt AgNO₃ is used as host matrix and TiO₂ as filler. From the filler concentration-dependent conductivity study, the maximum ionic conductivity at room temperature is obtained for 10 wt% of TiO₂. The real part of impedance (Z′) and imaginary part of impedance (Z″) are analyzed using an LCR meter. The dielectric properties of the highest conducting solid polymer electrolyte are analyzed using dielectric permittivity (ε′), dielectric loss (ε″), loss tangent (tan δ), real part of the electric modulus (M′), and imaginary part of the electric modulus (M″). It is observed that the dielectric constant (ε′) increases sharply towards the lower frequencies due to the electrode polarization effect. The maxima of the loss tangent (tan δ) shift towards higher frequencies with increasing temperature. The peaks observed in the imaginary part of the electric modulus (M″) due to conductivity relaxation shows that the material is ionic conductor. The enhancement in ionic conductivity is observed when nanosized TiO₂ is added into the solid polymer electrolyte.     

Role of Mn doping for obtaining of hexagonal phase in Ba0.98Zn0.02TiO3 ceramics

This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba_0.98Zn_0.02Ti_1−xMn_xO₃ (where, x= 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba_0.98Zn_0.02Ti_0.92Mn_0.08O₃ and a very feeble M–H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature.     

Influence of rare-earth ions on the structure and magnetic properties of barium W-type hexaferrite

Barium W-type hexaferrite with composition Ba_0.95R_0.05Mg_0.5Zn_0.5CoFe₁₆O₂₇ where R=Y, Er, Ho, Sm, Nd, Gd, and Ce ions has been prepared by the double-sintering ceramic technique. Structure of the prepared samples has been characterized by the X-ray diffraction (XRD) technique. The XRD patterns at room temperature show the presence of secondary phase with the intensity of the secondary phase increasing with increasing ionic radius of the rare earth (RE) ions. The variation of the magnetic susceptibility (χ_M) with temperature in the range 300–750 K at different magnetic field intensities (1280, 1733 and 2160 Oe) was studied by using Faraday's method. The results show that the Curie temperature (T_C) increases regularly with increasing RE ionic radius then decreases again, after which it reaches maximum value at Sm ion of radius ≈1.04 Å. This behavior was explained on the basis of the changes in Fe³⁺–O–Fe³⁺ superexchange interaction. The effective magnetic moment μ_eff. of the investigated samples was discussed in view of varying the RE element as well as the magnetization of different sublattices.     

Magnetic behaviour of the mixed spinel ferrite GaxFe1-xNiCrO4

Mössbauer, X-ray diffraction, dc magnetization and ac susceptibility measurements have been carried out in the spinel ferrite Ga_xFe_1-xNiCrO₄ (0⩽x⩽1) in different temperature ranges between 1.4 and 700 K. These measurements show A site occupation of Fe³⁺ ions and a coexistence of ferrimagnetic and frustrated (entropic) spins in this system for all x. The frustration in this system arises due to the random distribution of Fe³⁺ and diamagnetic Ga³⁺ ions on the A sites, and those of Ni²⁺ and Cr³⁺ ions on B sites.     

Structural stability,phase transition and dielectric properties of Pb(Mg1/2W1/2)1−xMxO3 (M = Zr,Sn, Ti) ceramics

ABSTRACT

Pb(Mg_1/2W_1/2)_1?xM_xO₃ (M?=?Zr,Sn,Ti) ceramics have been prepared by the conventional ceramic process. Their crystallographic, phase transition and dielectric properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer in this paper. The solubility of the tetra-valent cation in Pb(Mg_1/2W_1/2)_1?xM_xO₃ decreases in the sequence of Ti^4+?>?Zr^4+?>?Sn⁴⁺. The doping led to the phase transition from orthorhombic antiferroelectric to cubic paraelectric phase, the microscopic nature of which could be attributed to the contraction of Pb-O₁₂ dodecahedron. A definition of the ordering parameter of the cubic phase was deduced to quantitatively evaluate the B-site ordering degree which decreased with the increase in doping concentration. Anti-site disordering of Mg²⁺ and W⁶⁺ occurred in the high-level doping compositions, which led to the relaxor behavior observed in Ti⁴⁺-doped series with x?=?0.01 composition. Both of the maximum dielectric permittivity and loss in the paraelectric phase increased with the increasing doping concentration.     

Magnetic properties of ErxY1−xF3 solid solutions

The Er_xY_1−xF₃ (x=0.1, 0.2, 0.7, 0.9, 1) solid solutions were synthesized and characterized by X-ray powder diffraction and magnetic measurements. The crystal structure refinements done by the Rietveld profile method show that no significant change of the structure parameters with the erbium concentration occurs. On the basis of DC susceptibility measurements in the 2-300 K range the lowest four crystal field levels have been determined, giving the ground level magnetic moment value of 6.7 μ_B. Results of M(H) studies point to the presence of complex exchange interactions between erbium ions.     

Mössbauer study of an amorphous iron III flouride: FeF3, xHF (0 ⩽ x ⩽ 1)

A ferric amorphous flouride FeF₃, xHF with 0 ⩽ x ⩽ 1 synthesized by a soft chemistry reaction was studied by Mössbauer spectroscopy. The hyperfine characteristics are very close to those of deposited variety previously published: they show that the Fe³⁺ ions are surrounded by weakly distorted octahedra of flourine atoms. The study under external magnetic field indicates that the spins are randomly distributed: FeF₃, xHF has a speromagnetic behaviour like deposited amorphous FeF₃. Elsewhere the similarity between the two amorphous forms is confirmed by susceptibility measurements.     

Novel structural and magnetic properties of Mg doped copper nanoferrites prepared by conventional and wet methods

Nanoferrites of the general formula Cu_1−xMg_xFe₂O₄ with 0≤x≤0.6 were prepared by standard ceramic and wet methods. The structure was studied by X-ray diffraction and IR spectroscopy. The density and lattice constant were calculated and reported. The particle size of the prepared nanoferrites ranged from 8.7 to 41.1 nm. It was found that the lattice parameter decreases with increasing cation substitution of Mg²⁺ due to the difference of ionic radius and atomic mass. The dc magnetic susceptibility was measured out using Faraday's method. The magnetic hysteresis measurement was performed using a vibrating sample magnetometer. Magnetic constants such as Curie temperature, effective magnetic moment, saturation magnetization, remanent magnetization and corecivicty were obtained and reported. The magnetic constants decrease with increasing Mg²⁺, except the remanent magnetization which increased.     

Magnetic structure and phase diagram of the frustrated spinel Cd1−xZnxCr2Se4

In attempt to characterise the magnetic ordering in the whole composition range of the Cd_1−xZn_xCr₂Se₄ system, various magnetic measurements were performed on both crystalline and polycrystalline samples with 0?x?1. The magnetic properties of the system are typical of a ferromagnet below x=0.4 and of a complex antiferromagnet one above x=0.6. In this work the intermediate region was carefully studied. The variations of both M(T) and χ_ac at low fields suggest that transitions from ferromagnetic to Gabay–Toulouse ferromagnetic-spin-glass mixed phase at low temperature occur in the range 0.41?x?0.58. The high-temperature susceptibility measurements show that for the whole concentration range the system obeys Curie–Weiss laws. The results can be explained by the coexistence of competing interactions (ferromagnetic between nearest neighbours and antiferromagnetic between higher order neighbours) and disorder due to the random substitution between zinc and cadmium ions in the tetrahedral sites of the spinel lattice. An experimental magnetic phase diagram of the system is established.     

Dielectric,electrical transport and magnetic properties of Er3+substituted nanocrystalline cobalt ferrite

Erbium substituted cobalt ferrite (CoFe_2−xEr_xO₄; x=0.0–0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er³⁺) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe_2−xEr_xO₄ ceramics exhibit the spinel cubic structure without any impurity phase for x≤0.10 whereas formation of the ErFeO₃ orthoferrite secondary phase was observed for x≥0.15. All the CFEO samples demonstrate the typical hysteresis (M–H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (ε′) revealed the usual dielectric dispersion. The ε′–f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are ∼10⁻⁴ s and ∼0.61(±0.04), respectively. Electrical and dielectric studies indicate that ε′ increases and the dc electrical resistivity decreases as a function of Er content (x≤0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivity (σ_ac) analyses indicate the semiconducting nature and small polaron hopping.