Supertransferred Hyperfine Magnetic Fields at 111Cd Impurity Sites in Cd x Fe3−x O4 and Zn x Fe3−x O4

The hyperfine magnetic field at ¹¹¹Cd impurities substituting iron in the mixed spinels Cd _x Fe_3−x O₄ and Zn _x Fe_3−x O₄ has been determined by means of the Perturbed Angular Correlation technique. Compounds with different concentrations x were investigated as a function of temperature. The possibility of determining the lattice location of probes at octahedral or tetrahedral sites through the magnitude of the electric field gradient is analyzed. The measured hyperfine magnetic field at impurities in tetrahedral sites is discussed in terms of the populations of magnetic ions in the nearest neighbor sites. This revised version was published online in September 2006 with corrections to the Cover Date.     

Mössbauer and magnetic study of Mn2+- and Cr3+-substituted spinel magnesioferrites of the composition Mg1−xMnxFe2−2xCr2xO4

Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg_1?x Mn _x Fe_2?2x Cr_2x O₄ (x?=?0.0, 0.1, 0.2, 0.3, and 0.5) were investigated with X-ray diffraction (XRD), Mössbauer spectroscopy and magnetic measurements. The cation distribution inferred suggests that Mn²⁺ and Cr³⁺ ions dominantly occupy the A- and B-sites respectively. The gradual decrease of the hyperfine fields and Curie temperatures with increasing x reflects a gradual weakening in the AB exchange interaction. Mössbauer data of the sample with x = 0.5 is suggestive of cation clustering and/or superparamagnetism. The magnetization data is suggestive of Yafet-Kittel-type canted magnetism.     

Structural,textural, morphological,magnetic and electromagnetic study of Cu-doped NiZn ferrite synthesized by pilot-scale combustion for RAM application

The synthesis of the Ni_0.5-xZn_0.5-xCu_2xFe₂O₄ (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu²⁺ in a partial and proportional way to the Ni²⁺ and Zn²⁺ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 Å. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application.     

The magnetic properties of aligned M hexa-ferrite fibres

Aligned and random fibres of strontium hexaferrite (SrM, SrFe₁₂O₁₉) and barium hexaferrite (BaM, BaFe₁₂O₁₉) were manufactured by blow spinning from an aqueous inorganic sol–gel precursor, which was then fired to give the hexagonal ferrite fibre. Their magnetic properties were studied by VSM, investigating the evolution of these properties with firing and measurement temperature, and in particular the effects of fibre alignment. It has been predicted that aligned ferrite fibres will demonstrate an enhanced magnetisation along the axis of alignment with respect to perpendicular to the axis, and this has been demonstrated here for the first time. The optimum firing temperature was 1000 °C, at which point they still had submicron grains. In BaM random fibres M_s=63.8 emu g⁻¹ and H_c=428.1 kA m⁻¹, and in SrM random fibres M_s=63.3 emu g⁻¹ and H_c=452.8 kA m⁻¹, high values for polycrystalline materials. Fibres aligned parallel to the applied field had saturation magnetisation (M_s) values equal to those of the random fibres, whilst fibres aligned perpendicular to the field had M_s values 62% and 75% lower, for BaM and SrM, respectively. There was no change in coercivity (H_c) between random or aligned fibres of any orientation, and fibres aligned 45° and parallel to H appeared identical. Therefore, properties along the axis of alignment were superior when compared to measurements perpendicular to the axis of alignment, giving a directionality to the magnetisation in an otherwise randomly oriented ferrite material.     

Magnetic interactions in Cu-substituted manganese ferrites

A series of Mn_1−xCu_xFe₂O₄, with x=0, 0.25, 0.50, 0.75 and 1.0, spinel ferrites were prepared by standard ceramic method, to study the effect of compositional variation on magnetic susceptibility, saturation magnetization (M_s), Curie temperature (T_c) and magnetic moments (μ_B). The Curie temperatures have been evaluated by measuring the ac susceptibility using the mutual inductance technique. On increasing Cu contents from 0.0 to 0.50, the saturation magnetization increases while the Curie temperature decreases. On further increase in Cu contents, x>0.50 a decreasing trend in M_s is exhibited while T_c continues to decrease. This effect can be partially related to the low magnetic moments of Cu⁺² ions. The dominant interaction in all ferrite samples is A-B interaction which is due to the negative values of the characteristic temperature θ(K) showing that the magnetic ordering is antiferromagnetic. The Y-K angle increases gradually with increasing copper contents and extrapolates to 90° for CuFe₂O₄. From the computation of Y-K angles for Mn_1−xCu_xFe₂O₄, it can be concluded that the mixed copper ferrites exhibit a non-collinearity of the Y-K type while MnFe₂O₄ shows a Neel type of ordering.     

Ferroelectricity from iron valence ordering in rare earth ferrites?

The possibility of multiferroicity arising from charge ordering in LuFe₂O₄ and structurally related rare earth ferrites is reviewed. Recent experimental work on macroscopic indications of ferroelectricity and microscopic determination of coupled spin and charge order indicates that this scenario does not hold. Understanding the origin of the experimentally observed charge and spin order will require further theoretical work. Other aspects of recent research in these materials, such as geometrical frustration effects, possible electric‐field‐induced transitions, or orbital order are also briefly treated.

     

ICP-MS法测定MnZn铁氧体中Si和P

研究了电感耦合等离子体质谱(ICP-MS)法测定锰锌铁氧体中硅和磷元素的分析方法。样品用硝酸+盐酸经微波溶解,用超纯水稀释后直接进入ICP-MS法进行测定。通过向八极杆碰撞/反应池(ORS)中引入氦气,消除高盐基体带来的多原子离子质谱干扰,采用Y为内标元素校正基体效应所产生的影响,优化了仪器的最佳工作参数。采用NIST SRM 362和NIST SRM 364验证了方法的准确性,测定结果与标准物质所提供的参考值一致。硅和磷元素的检出限分别为0.91和0.27μg·L-1。     

Influence of the Mg-content on the cation distribution in cubic MgxFe3−xO4 nanoparticles

The influence of the Mg-content on the structural and magnetic properties of cubic Mg_xFe_3−xO₄ nanoparticles prepared by combustion reaction was investigated using X-ray diffraction, transmission electron microscopy (TEM), Mössbauer spectroscopy, and Raman spectroscopy. Lattice parameter, nanoparticle size, and cation (Mg²⁺, Fe³⁺) distribution were quantified as a function of the Mg-content in the range 0.5≤x≤1.5. We found a mixed-like spinel structure at the smaller x-value end whereas the inverse-like spinel structure dominates samples with larger x-values. Moreover, in the x-value range investigated (0.5≤x≤1.5) we found no change in the quadrupole splitting and isomer shift values, though the hyperfine field decreases as the x-value increases. The splitting of the A_1g Raman mode was used to both quantify the Mg²⁺/Fe³⁺ contents in the tetrahedral site and obtain the cation distribution in the Mg_xFe_3−xO₄ structure. The cation distribution obtained from the Raman data is in very good agreement with the cation distribution obtained from the Mössbauer data.     

纳米锰锌铁氧体的制备及在TPV中的应用

采用化学共沉淀法制备纳米锰锌铁氧体纳米颗粒,并用油酸进行表面改性,有效地阻止了纳米颗粒的团聚;改性后团聚体的粒径明显减小,提高了其在TPV中的分散性.将制备好的纳米颗粒作为填料改性TPV,通过一系列试验发现,油酸改性的锰锌铁氧体纳米颗粒比未改性的纳米颗粒更能提高TPV的拉伸强度和断裂伸长率.