Effect of Y2O3 doping on the electrical transport properties of Sr2MnNiFe12O22 Y-type hexaferrite

Y₂O₃ doped Y-type composite hexa-ferrites Sr₂MnNiFe₁₂O₂₂ + xY₂O₃ (x = 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) were synthesized successfully using sol-gel auto combustion technique. X-ray diffraction analysis reveals Y-type hexagonal structure with few traces of secondary phases. The decrease in grain size as a function of Yttrium content is attributed to the fact that Yttrium acts as a grain inhibitor. The DC resistivity was observed to increase with increasing Yttrium-contents due to the unavailability of Fe³⁺ ions at octahedral sites. Activation energy showed that the samples with high resistivity have high value of activation energy and vice versa. Permittivity decreases with the increase of frequency following Maxwell Wagner Model. In addition, the doped samples exhibit very low dielectric constant and low loss tangent in frequency range 20 Hz–1 MHz. The sample x = 5 wt% exhibit the lowest value of dielectric constant. The variation in imaginary part of dielectric constant and loss tangent with frequency show normal dielectric behavior for all the samples. The frequency dependent ac conductivity increases with increase in frequency and decrease with Y₂O₃ doping. These characteristics may be suitable for their potential applications in electromagnetic attenuation materials and microwave devices. The conductivity mechanism so determined was hopping mechanism. The dc resistivity of the doped ferrites measured in our case is about 10¹⁰ Ω-cm that meets the requirement for fabrication of components by electroplating.     

The influence of Nd-Co substitution on the magnetic properties of non-stoichiometric strontium hexaferrite nanoparticles

Non-stoichiometric Nd-Co substituted hexaferrites of composition Sr_1−xNd_xFe_12(1−x)Co_xO₁₉ (x=0-0.4) were prepared by the self-propagating combustion method and subsequent heat treatments. Structural characterization of samples showed that the M-type hexagonal structure can be maintained for substitutions x<0.4 without the segregation of secondary phases on samples calcined at 1100 °C. The crystallites sizes range between 50 and 70 nm. Mössbauer spectroscopy results indicate that the iron vacancies are not evenly distributed over the lattice and that Co/Fe substitution mainly takes place in site 4f2. Magnetic measurements reveal that values of saturation magnetization M_S increased from 72 to 76 Am²/kg (x=0-0.2), while coercivity H_c increased from 26.40 to 58.70 A/m (x=0-0.3). Nd-Co substitutions enhance magnetic properties in deficient iron Sr hexaferrites.     

Effect of the Zn2+ distribution on the magnetic properties of Ba2Zn2Fe12O22(Zn2-Y) hexaferrite investigated by thermal-scan Mössbauer spectroscopy

Summary The role of the cation distribution on the magnetic characteristics of Ba₂Zn₂Fe₁₂O₂₂(Zn₂-Y) hexaferrite has been analysed by using M?ssbauer techniques. For this purpose we developed a low-cost microcomputer-controlled thermal-scan M?ssbauer apparatus that allows accurate measurements of the Curie temperature. The measuring times are much shorter than those attained with previously described similar apparata. The variation of the Curie temperature with the sintering temperature of Zn₂-Y has been correlated with different cation distributions of Zn²⁺ among the two tetrahedral sublattices present in the Y-structure.

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Riassunto Utilizzando tecniche M?ssbauer si è analizzato il ruolo della distribuzione cationica sulle proprietà magnetiche dell’esaferrito Ba₂Zn₂Fe₁₂O₂₂ (Zn₂-Y). A questo scopo è stato messo a punto un apparato a basso costo controllato da microcomputer per analisi termiche che utilizza l’effetto M?ssbauer. L’apparecchiatura consente misure di temperatura di Curie con tempi di misura inferiori a quelli di apparecchiature simili descritte in precedenza. La variazione della temperatura di Curie al variare della temperatura di sinterizzazione osservata nell’esaferrito Zn₂-Y è stata correlata con la distribuzione del catione Zn²⁺ tra i due siti tetraedrici presenti nella struttura Y.

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Резюме Используя технику эффекта Мессбауэра, анализируется роль распределения катионов на магнитные свойства гексаферрита Ba₂Zn₂Fe₂O₂₂(Zn₂-Y). Для этой цели предлагается недорогостоящая установка, контролируемая компьютером для тырмического анализа, которая исрользует зффект Мессбауэра. Предложенная установка позволяет точно измерять температуру Кюри, причем времена измерений оказываются существенно меныше, чем у родобных установок, орисанных в литературе. Изменение температуры Кюри в завицимости от температурм спекания Zn₂-Y коррелирует с различными распределениями катионов Zn²⁺ между двумя тетраздрическими подрешетками, присутстствующими в Y-структуре.

     

Model for the low magnetic moment of Ba2Zn2Fe12O22 (Zn2Y)

The experimental value of the spontaneous magnetic moment μ(0) at OK of Zn₂Y is 8% lower than the theoretical one. This reduction of the moment is ascribed to a local spin reversal on octahedral 3b-sites due to a high Zn-concentration in the S-block.     

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.     

Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe_(12)O_(22)

We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe_(12)O_(22),which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K.Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field,resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe_(12)O_(22)exhibits an anomalous magnetoelectric memory effect:the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K.We ascribe this memory effect to the pinning of multiferroic domain walls,where spin chirality and structure are preserved even in the nonpolar collinear spin state.     

Hard magnetic properties of nanosized Sr(Fe,Al)12O19 hexaferrites obtained by Pechini method

In this work, we report the magnetic properties of isotropic M-type SrFe_12−xAl_xO₁₉ (x=0.0,1.5) hexaferrites synthesized by means of Pechini method. A polycrystalline distribution of fine grains was verified by Transmission Electron Microscopy for both compositions, with average sizes below 60 nm. Remarkable coercivity values within the range 500–850 kA/m were attained as a consequence of a combined effect of grain size refinement together with an enhancement of the anisotropy field afforded by the incorporation of the Al³⁺ cations into the hexagonal crystal structure.     

Magnetic properties of ultra-fine particles of Mn0.5Fe0.5Fe2O4 spinel system

A systematic study of the magnetic properties of ultra-fine particles of Mn_0.5Fe_0.5Fe₂O₄ spinel system has been undertaken. The effect of temperature on the magnetic properties of particles and the ferrofluid has been studied. Analysis of the data yields information on the anisotropy constant, particle size distribution and superparamagnetic behaviour. The results are explained on the basis of existing theories.     

Effect of pH value on the structural and magnetic properties of nanocrystalline strontium hexaferrite thin films

Strontium hexaferrite SrFe₁₂O₁₉ thin films have been synthesized at different pH, adjusted by NH₄OH, on the Si (1 0 0) substrate using a spin coating sol-gel process. Fourier transform infrared spectroscopy analysis and theoretical calculations were conducted for determination and controlling metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer were applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe₁₂O₁₉ thin films. Using the solution with pH 7, the approximately single phase strontium hexaferrite thin films with optimum physical properties can be obtained at calcination temperature of 800 °C. The SrFe₁₂O₁₉ thin films derived from the solution with pH 7 after calcination at 800 °C exhibited crystallite size of 42 nm and magnetic properties of M_s=267 emu/cm³ (at 10 kOe), M_r=134 emu/cm³ and H_c=4290 Oe.     

Structure and magnetic properties of Ni0.5Zn0.5Mn0.5-xMoxFe1.5O4 ferrites prepared by sol-gel auto-combustion method

A series of Mo doped Ni-Mn-Zn ferrites compounds with the formula Ni_0.5Zn_0.5Mn_0.5-xMo_xFe_1.5O₄ (x = 0, 0.025, 0.05, 0.075 and 0.1) were first synthesized by sol-gel auto-combustion method. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM) analysis were carried out to characterize the microstructural and magnetic properties of ferrites. Rietveld refinement of X-ray diffraction data confirmed the formation of cubic spinel structure and the emergence of FeMoO₄ phase with the substitution of Mo⁶⁺ contents. The grain size increased remarkably due to the formation of the liquid phase. The saturation magnetization (M_s) increased while the coercivity (H_c) decreased from 67.3 to 12.1 Oe due to the decrease of magneto-crystalline anisotropy constant. The initial permeability (μ_i) increased significantly from 34 (x = 0) to 114 (x = 0.075) and later decreased for x = 0.1. In our experiment, Ni_0.5Zn_0.5Mn_0.425Mo_0.075Fe_1.5O₄ ferrite presented the best microstructure and soft magnetic properties.     

Detection of coherent magnons via ultrafast pump-probe reflectance spectroscopy in multiferroic Ba0.6Sr1.4Zn2Fe12O22

We report the detection of a magnetic resonance mode in multiferroic Ba0.6Sr1.4Zn2Fe12O22 using time-domain pump-probe reflectance spectroscopy. Magnetic sublattice precession is coherently excited via picosecond thermal modification of the exchange energy. Importantly, this precession is recorded as a change in reflectance caused by the dynamic magnetoelectric effect. Thus, transient reflectance provides a sensitive probe of magnetization dynamics in materials with strong magnetoelectric coupling, such as multiferroics, revealing new possibilities for application in spintronics and ultrafast manipulation of magnetic moments.     

Effect of Fe/Pb molar ratio on the structure,magnetic and dielectric properties of PbFe12O19 nanoparticles

In this paper, lead hexaferrite (PbFe₁₂O₁₉) nanoparticles were synthesized by sol-gel method. In order to prepare PbFe₁₂O₁₉ nanoparticles, the metal nitrates with Fe/Pb?=?8, 10, 11, 12, 14 ratios and citric acid were used. The structure, morphology, magnetic, and dielectric properties of PbFe₁₂O₁₉ nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM) and LCR meter. XRD results revealed that the samples with Fe/Pb?≤?10 and Fe/Pb?>?10 have single-phase hexaferrite and hematite (α- Fe₂O₃) structures, respectively. As a result, the sample with Fe/Pb?=?10 is single-phase and shows the highest values of the saturation magnetization and remanence magnetization. We found that the values of dielectric constant (ε′) and dielectric loss (ε″) increase with an increase in the Fe/Pb molar ratio from 8 to 12 and then decreases with an increase of Fe/Pb molar ratio to 14. The variation of ac conductivity (σ_ac) with frequency ranging from 1?kHz to 200?kHz showed that electrical conductivity in these ferrites is mainly due to the electron hopping mechanism.     

Ni0.8Zn0.2Fe2O4和CO2Y添加Ni0.8Zn0.2Fe2O4磁性质对比研究

采用固相反应法制备了Ni0.8Zn0.2Fe2O4和2wt％ Co2Y添加Ni0.8Zn0.2Fe2O4铁氧体多晶样品,并对样品的磁性质进行了研究.实验发现,添加Co2Y后,铁氧体的磁损耗明显下降,相同条件下Q值增大到原来的3倍左右.对添加Co2Y引起铁氧体磁损耗下降的原因进行了讨论,认为主要是钴离子掺杂引起的铁氧体磁滞损耗明显降低所导致的.     

Fe掺杂对自旋梯状化合物Sr14(Cu1－yFey)24O41的结构和电输运性质的影响

采用常规的固相合成法分别制备了Fe³⁺掺杂和2/3Fe³⁺+1/3Fe²⁺混合Fe离子掺杂的两组Sr₁₄(Cu_1-yFe_y)₂₄O₄₁系列样品.X射线衍射分析显示，当Fe³⁺离子的掺杂量y≤0.03以及2/3Fe³⁺+1/3Fe²⁺混合Fe离子掺杂量y≤0.02时，样 关键词： 强关联电子系统 自旋梯状结构化合物 晶体结构 电输运性质     

Structural and magnetic properties of Ti12M clusters (M=Sc to Zn)

The geometries, electronic, and magnetic properties of the 3d atom doped icosahedron (ICO) Ti₁₂M (M=Sc to Zn), where a dopant atom replaces either the centra l(Ti₁₂M^c) or surface (Ti₁₂M^s) Ti atom in ICO Ti₁₃ cluster, have been systematically investigated by using the density functional theory. The structures of all the optimized Ti₁₂M^c and Ti₁₂M^s clusters are distorted ICO. Sc, Ni, Cu, and Zn atoms prefer to displace surface Ti atom, V, Cr, Mn, and Fe atoms prefer to displace central Ti atom. The position of impurity atom depends on the strength of the interaction between the central atom and the surface atoms. As compared to the pure Ti₁₃ cluster, Ti₁₂M^c and Ti₁₂M^s (M=V, Fe, Co, and Ni) clusters are more stable, Ti₁₂M^c and Ti₁₂M^s (M=Sc, Cr, Mn, Cu, and Zn) are less stable. Both Ti₁₂Ni^s and Ti₁₂Ni^c are magic clusters, which originate from their electronic as well as geometric closed shells. Because the exchange interaction prevails over the crystal field in Ti₁₂M clusters, the valence electrons fill molecular orbitals in terms of Hund’s rule of maximum spin.     

Substitution effect of Ba at the Sr sites in Sr(Fe,Re)O3

We study ?-meson production in nuclei to investigate the in-medium modification of the ?-meson spectral function at finite density. We consider ( ${\bar p},\phi$ ), (γ,p) and (π ^???, n) reactions to produce a ?-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, ?-mesic nuclei, are also studied. For strong absorptive interaction cases, we need to know the spectrum shape in a wide energy region to deduce the properties of ?.     

57Fe hyperfine interaction parameters and selected magnetic properties of high purity MFe12O19 (M=Sr,Ba)

Much of the confusion regarding the ⁵⁷Fe Mössbauer spectroscopic hyperfine parameters of SrFe₁₂O₁₉ and BaFe₁₂O₁₉ at 300 K has been removed by means of an interlaboratory investigation of well-characterized samples prepared from high purity starting materials. In contrast to previous investigations, the contributions of each of the five Fe sublattices to the Mössbauer spectrum are discernible at 300 K and five components are necessary for an adequate fit of the data. The relative magnitudes of the hyperfine fields, H_n, and isomer shifts, δ, are as follows: for SrFe₁₂O₁₉ and BaFe₁₂O₁₉: H_n(2b)< H_n(12k)<H_n(4f₁) <H_n(2a)<H_n(4f₂), for SrFe₁₂O₁₉ δ(4f₁≤δ(2b)<δ(12k)δ(2a)<δ(4f₂), and for BaFe₁₂O₁₉ δ4f₂), and for BaFe₁₂O₁₉ δ(4f₁<δ(4f₁)<(12k) < δ(4f₂)<δ(2a). The above assignment is based on considerations of both magnetic and crystal/chemical structures.The high purity starting materials seem to have appreciable influences on both hyperfine interaction parameters and bulk magnetic properties as observed by others for spinel and garnet ferrites.     

一维Ni0.5Zn0.5Fe2O4/SiO2复合纳米结构的制备及其磁性能

采用溶胶-凝胶法结合静电纺丝技术制备了Ni_0.5Zn_0.5Fe₂O₄/SiO₂复合纳米纤维.利用热重-差热分析、X射线衍射、场发射扫描电镜、高分辨透射电镜和振动样品磁强计研究了前驱体纤维的热分解及相转化过程以及焙烧温度和SiO₂含量对目标纳米纤维的相组成、微观结构、形貌及磁性能的影响.结果表明,在450 ℃焙烧时,立方尖晶石结构已基本形成.随着焙烧温度由450 ℃升高到100     

Effect of Co substitution on the structural and magnetic properties of Zn–W hexaferrite

The polycrystalline samples of the composition Zn_2−XCo_XBaFe₁₆O₂₇ were prepared by the usual ceramic technique with X=0.4, 0.6, 0.8, 1, 1.2, 1.4 and 1.6. The samples were sintered at 1300 °C for 8 h. The X-ray diffraction patterns confirm the presence of single W-hexagonal phase. The lattice parameters c and a was found to increase by increasing Co content whereas the X-ray density decreases and porosity increases by increasing Co content. The value of saturation magnetization (σ) decreases by increasing Co content due to the decrease of super-exchange interaction. The magnetic moment of the sample were calculated and it showed that in Zn_2−XCo_XBaFe₁₆O₂₇ nearly all Co²⁺ ions are distributed among the octahedral sites of spinel S block. The M–H hysteresis loop for all the samples are clearly showing low coercivity, indicating that all the samples belongs to the family of soft ferrite. The values of coercivity increases by increasing Co content. The far infrared absorption spectrum showed the presence of three absorption bands corresponding to tetrahedral, octahedral and hexahedral sites.