Cation distributions estimated using the magnetic moments of the spinel ferrites Co_(1-x)Cr_xFe_2O_4 at 10K

（A）[B]2O4 ferrite samples with the composition COl_xCrxFe204 （0.0 ≤ x ≤1.0） are prepared using a hydrothermal method, and subjected to calcining in a tube furnace with an argon-flow at 1673 K for 2 h. X-ray diffraction patterns indicate that each of all the samples has a single phase cubic spinel structure with a space group of Fd3m. Magnetic measurements show that the saturation magnetization decreases with as the Cr content x increases. The cation distribution of the samples is estimated by fitting the dependence of the magnetic moments on x at l 0 K, using the quantum mechanical model previously proposed by our group. The calculated sum of the content values of the Cr3＋ and Cr2＋ cations occupying the （A） sites increases as the value of x increases. In the fitting process, the magnetic moment directions of the Cr3＋ and Cr2＋ cations are assumed to be antiparallel to those of the Fe and Co cations, respectively, which is in accordance with Hund＇s rules.     

稀土元素La掺杂BaFe12O19微结构和磁性能的研究术

用固相法制备了镧掺杂M型钡铁氧体（Ba1--xLaxFel2O19,x=0．0-0．6）,针对不同取代量与不同温度的烧结,研究取代量和温度对钡铁氧体微结构和磁性能的影响．在烧结温度为1100-1175℃,当X=0．0-0．6时,样品主要有单一的六角M型钡铁氧体相构成．SEM表明,La离子的加入不会影响钡铁氧体微观形貌．在磁性能方面,随着La离子的增加,钡铁氧体的饱和磁化强度先增加后减小,矫顽力逐渐增加．在同一取代量下,钡铁氧体的饱和磁化强度随烧结温度升高呈现上升趋势,矫顽力随着烧结温度的升高而降低．饱和磁化强度在x=0．2,烧结温度1175℃时达到最大值62．8emu／g,矫顽力在x=0．6,烧结温度1125℃时达到最大值3911．5Oe．     

尖晶石铁氧体TixNi1-xFe2O4中阳离子分布和Ti离子磁矩的实验研究

采用固相反应法制备了系列样品Ti_xNi_1-xFe₂O₄ (x=0.0, 0.1, 0.2, 0.3, 0.4). 室温下的X射线衍射谱表明样品全部为(A)[B]₂O₄型单相立方尖晶石结构, 属于空间群Fd3m. 样品的晶格常数随Ti掺杂量的增加而增大. 样品在10 K温度下的比饱和磁化强度σ_S随着Ti掺杂量x的增加逐渐减小. 研究发现, 当Ti掺杂量x≥ 0.2时, 磁化强度σ随温度T的变化曲线出现两个转变温度T_L和T_N. 当温度低于T_N时, 磁化强度明显减小; 当温度达到T_N时, dσ/dT具有最大值. σ-T曲线的这些特征表明, 由于Ti掺杂在样品中出现了附加的反铁磁结构. 这说明样品中的Ti离子不是无磁性的+4价离子, 而是以+2和+3价态存在, 其离子磁矩的方向与Fe和Ni离子的磁矩方向相反. 利用本课题组提出的量子力学方势垒模型拟合样品在10 K温度下的磁矩, 得到了Ti, Fe和Ni三种阳离子在(A)位和[B]位的分布情况, 并发现在所有掺杂样品中, 80%的Ti离子以+2价态占据尖晶石结构的[B]位.     

Doping effects on structural and magnetic evolutions of orthoferrite SmFe（1-x） Alx O3

The structural and magnetic properties of SmFeO3 with B site substitution of non-magnetic atom A1 are investigated. The x-ray diffraction patterns show that SmFe（1-x）AlxO3 remains an orthorhombic structure within the whole doping range, and the unit-cell volume decreases monotonically with the increase of doped A1 concentration. Besides, the octa- hedral tilting distortions of FeO6 are found to be alleviated while the tolerance factor increases. However, the relationship between the lattice parameters and Al concentration is observed to deviate from Vegard＇s rule, and this may be caused by magnetostriction effects. For the doping content values in a range 0 〈 x 〈 0.6, the ferromagnetism, antiferromagnetism, and paramagnetism are observed to occur continuously. Moreover, the magnetization and the spin reorientation temperature （Tk） decrease monotonically as Al content value increases. With the doping content values being x = 0.8 and 1.0, these compounds only show paramagnetic behavior.     

Microstructure and magnetic properties of CoFe_2O_4 thin films deposited on Si substrates with an Fe_3O_4 under-layer

The microstructure and magnetic properties of cobalt ferrite thin films deposited by the sputtering method on an Fe3O4 under-layer were investigated at different post-annealing temperatures.Results show that the Fe3O4 under-layer can accelerate the grain growth of cobalt ferrite films due to the phase transformation of the Fe3O4 under-layer at about 400°C-500°C.By introducing the Fe3O4 under-layer,cobalt ferrite nanocrystalline thin films with high coercivity can be obtained at lower post-annealing temperat...     

Structural and magnetic properties of turmeric functionalized CoFe_2O_4 nanocomposite powder

The structural and magnetic properties of the synthesized pure and functionalized CoFe_2O_4 magnetic nanoparticles(NPs) are studied by analyzing the results from the x-ray diffraction(XRD), transmission electron microscopy(TEM), FT–IR spectroscopy, thermogravimetry(TG), and vibrating sample magnetometer(VSM). To extract the structure and lattice parameters from the XRD analysis results, we first apply the pseudo-Voigt model function to the experimental data obtained from XRD analysis and then the Rietveld algorithm is used in order to optimize the model function to estimate the true intensity values. Our simulated intensities are in good agreement with the experimental peaks, therefore, all structural parameters such as crystallite size and lattice constant are achieved through this simulation. Magnetic analysis reveals that the synthesized functionalized NPs have a saturation magnetization almost equal to that of pure nanoparticles(PNPs). It is also found that the presence of the turmeric causes a small reduction in coercivity of the functionalized NPs in comparison with PNP. Our TGA and FTIR results show that the turmeric is bonded very well to the surface of the NPs. So it can be inferred that a nancomposite(NC) powder of turmeric and nanoparticles is produced. As an application, the anti-arsenic characteristic of turmeric makes the synthesized functionalized NPs or NC powder a good candidate for arsenic removal from polluted industrial waste water.     

应变对钴铁氧体电子结构和磁性能影响的第一性原理研究

尖晶石型钴铁氧体(CoFe₂O₄)因具有良好的电磁性质, 广泛应用于计算机技术、航空航天及医学生物等领域. 特别是钴铁氧体薄膜在磁电复合材料中具有良好的应用前景. 本文基于密度泛函理论的第一性原理平面波赝势法, 结合广义梯度近似, 通过采用更接近于实验上外延生长的二维应变模型, 研究了钴铁氧体薄膜的结构稳定性、电子结构和磁性能. 结果表明: 在二维应变作用下, 反尖晶石结构的钴铁氧体比正尖晶石结构的稳定, 但是与平衡基态相比, 两者能量差减小, 这表明在应变作用下, 八面体晶格中的Co²⁺离子与四面体晶格中的Fe³⁺离子更容易进行位置交换, 形成混合型结构的钴铁氧体; 同时随着应变的增大, 钴铁氧体的能带带隙减小, 晶格中的原子磁矩发生变化, 但总磁矩变化不明显. 关键词： 尖晶石型钴铁氧体 第一性原理 电子结构 磁性能     

Co_(1-x)Zn_xFe_2O_4 nanofiber: Synthesized by electrospinning and its magnetic properties

Well-aligned and uniform Coo.sZno.2Fe204 nanofibers （NFs） are prepared by electrospinning via sol-gel and sub- sequent heat treatment. Each of the as-spun NFs has a diameter of about 300 nm and a smooth surface morphology. The scanning electron microscope （SEM） image shows that the diameter decreases to 70 nm after the Coo.sZno.2Fe204 NF has been annealed at 650℃ for 3 h. The structure and chemical of Co0.8Zn0.2Fe204 NF are investigated by X- ray diffraction （XRD） and energy dispersive X-ray spectroscopy （EDS）, respectively. Single phase cubic spinel structure, Coo.sZno.2Fe204 NF, is successfully obtained after having been calcined at 550 ~C in air for 3 h, and a reduced lattice constant of the Coo.8Zno.2Fe204 NF provides the evidence of effective Zn2＋ substitution. The magnetic measurements show that the substitution of Zn2＋ for Co2＋ , i.e., the introduction of non-magnetic Zn2＋ ions into A sites, can increase the saturation magnetization （Ms） and reduce the coercivity （He）. The obtained Hc results of different samples reveal that the critical single-domain size of the Co0.8Zn0.2Fe204 NF is approximately 44 nm. By doping Zn2＋ with different concentra- tions, the morphologies of Co1-xZnxFe2O4 （0 〈 x 〈 0.5） NFs do not show obvious changes. For magnetic properties, the Ms increases and Hc decreases monotonically, respectively.     

Impact of zinc substitution on the structural and magnetic properties of chemically derived nanosized manganese zinc mixed ferrites

Mn_1−xZn_xFe₂O₄ nanoparticles (x=0-1) were synthesized by wet chemical co-precipitation techniques. X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The elemental analysis was conducted using energy-dispersive spectrum and inductively coupled plasma analysis. The magnetic properties such as magnetization and coercivity were measured using vibrating sample magnetometer. The observed magnetization values of the nanoparticles were found to be lower compared to the bulk counterpart. The magnetization showed a gradual decrease with zinc substitution except for a small increase from x=0.2 to 0.3. The Curie temperature was found to be enhanced in the case of ferrites in the nanoregime. The variation in lattice constant, reduced magnetization values, variation of magnetization with zinc substitution, the presence of a net magnetic moment for the zinc ferrite and the enhancement in Curie temperature in Mn_1−xZn_xFe₂O₄ all provide evidence to the existence of a metastable cation distribution together with possible surface effects at the nanoregime.     

Growth of monodisperse nanospheres of MnFe_2O_4 with enhanced magnetic and optical properties

Highly dispersive nanospheres of MnFe204 are prepared by template free hydrothermal method. The nanospheres have 47.3-nm average diameter, narrow size distribution, and good crystallinity with average crystallite size about 22 nm. The reaction temperature strongly affects the morphology, and high temperature is found to be responsible for growth of uniform nanospheres. Raman spectroscopy reveals high purity of prepared nanospheres. High saturation magnetization （78.3 emu/g）, low coercivity （45 Oe, 10e = 79.5775 A.cm-1）, low remanence （5.32 emu/g）, and high anisotropy constant 2.84 × 10^4 J/m3 （10 times larger than bulk） are observed at room temperatures. The nearly snperparamagnetic behavior is ~ spin due to comparable size of nanospheres with superparamagnetic critical thameter Dcr spm The high value of Keff may be due to coupling between the pinned moment in the amorphous shell and the magnetic moment in the core of the nanospheres. The nanospheres show prominent optical absorption in the visible region, and the indirect band gap is estimated to be 0.98 eV from the transmission spectrum. The prepared Mn ferrite has potential applications in biomedicine and photocatalysis.     

纳米Zn_(0.6)Co_xFe_(2.4-x)O_4晶粒的结构相变与磁性研究

采用溶胶 凝胶自燃烧法制备了纳米尺度的锌钴铁氧体Zn0 6 CoxFe2 4 -xO4 (x =0— 0 30 )粉体 ,分别在不同温度下进行了热处理 ,利用x射线衍射仪 (XRD)和振动样品磁强计 (VSM)对其物相结构和磁性进行了测量和分析 .实验结果表明 ,锌钴铁氧体Zn0 6 Co0 1 5Fe2 2 5O4 在 5 5 0— 80 0℃温度区间出现α Fe2 O3过渡相 ,在高于 80 0℃温度时生成单一尖晶石相锌钴铁氧体 ;随钴含量的增加 ,Zn0 6 CoxFe2 4 -xO4 的比饱和磁化强度先增后减 ,x =0 0 75— 0 1 5比饱和磁化强度较高 ;Zn0 6 CoxFe2 4 -xO4 在 1 30 0℃时x =0 0 75的矫顽力为 4 75 2 0A m ,x≥ 0 1 5时矫顽力在 1 2 0 0℃附近随温度缓慢上升 ,在 1 2 0 0— 1 30 0℃之间为平台状态 ,并且随钴含量的增加 ,矫顽力略有升高 .在x =0 1 0附近 ,可同时获得较高的比饱和磁化强度和较高的矫顽力     

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.     

(Nd_(1-x)Er_x)_2Co_(15.5)V_(1.5)的结构转变与磁性

利用电弧熔炼制备了 (Nd1 xErx) 2 Co1 5 5V1 5(x=0— 1 0 )化合物样品 .通过x射线衍射分析和磁性测量研究了Er替代Nd2 Co1 5 5V1 5中的Nd时对化合物结构和磁性的影响 .研究结果表明 ,低Er含量 (x <0 4 ) ,化合物为Th2 Zn1 7型结构 ;高Er含量时 (x >0 5 ) ,化合物转变为Th2 Ni1 7结构 ;Er含量为x =0 4和 0 5时 ,两种结构共存 .两种结构的晶胞参数a ,c和晶胞体积V随着Er含量的增加都呈现递减的趋势 .随着Er含量的增加 ,(Nd1 xErx) 2 Co1 5 5V1 5化合物的居里温度和饱和磁化强度都单调下降 .(Nd1 xErx) 2 Co1 5 5V1 5化合物的室温各向异性由低Er含量时的易锥型转变为高Er含量时的易轴型 .x =0— 0 5的化合物在温度升高时发生自旋重取向转变 ,自旋重取向温度Tsr随Er含量的增加而减小     

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.     

Tailoring the optical and magnetic properties of La-BaM hexaferrites by Ni substitution

We investigate the impact of Ni insertion on the structural,optical,and magnetic properties of Ba_0.8La_0.2Fe_12-xNi_xO₁₉hexaferrites(Ni substituted La-BaM hexaferrites).Samples were prepared using the conventional co-precipitation method and sintered at 1000℃for 4 hours to assist the crystallization process.An analysis of the structure of the samples was carried out using an x-ray diffraction(XRD)spectrometer.The M-type hexagonal structure of all the samples was confirmed using XRD spectra.The lattice parameters a and c were found to be in the ranges of 5.8925±0.001 nm–5.8952±0.001 nm and 23.2123±0.001 nm–23.2219±0.001 nm,respectively.The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra,respectively.EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio.A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm–1100 nm.The optical energy bandgap of the samples was found to be in the range of 1.21 eV–3.39 eV.The M–H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe–60 kOe.A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz.This high value of saturation magnetization is due to the substitution of La3+ions at the spin-up(12k,2a,and 2b)sites.The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites.Therefore,we suggest that the prepared samples are suitable for use in magneto-optic applications.     

Structural and magnetic properties of BiFe_(1-x)Cr_xO_3 synthesized samples

Chromium doping effects on the structure and the magnetic properties of bismuth ferrite BiFe1-xCrxO3 （x = 0-0.3） （BFCxO） polycrystalline samples are examined. The Perovskite-type oxide samples are synthesized by the conventional solid state reaction at a high pressure of 7 GPa and a temperature of 1273 K. The X-ray powder diffraction patterns at room temperature show that all the samples with x = 0.0-0.3 are described by the rhombohedral structure. In the meantime, it is revealed that the doping of Cr can induce noticeable lattice distortions in the doping samples, and the largest distortion is observed in the case x = 0.1. The magnetic hysteresis loops measured at room temperature exhibit week ferromagnetic behaviors of the samples and the magnetization is found to increase with the increase in Cr concentration. The temperature- dependent magnetization curves indicate antiferromagnetic features in samples. Moreover, Cr-doping tends to reduce the ordering temperature.     

稀土掺杂对钴铁氧体电子结构和磁性能影响的理论研究

尖晶石型铁氧体是十分重要的磁性材料之一, 具有独特的物理性质、化学特性、磁学特性和电子特性. 其中尖晶石型钴铁氧体具有较好的电磁性质而被广泛应用. 本文基于密度泛函理论(DFT) 的第一性原理平面波赝势法, 结合广义梯度近似(GGA+U), 研究了CoRE_0.125Fe_1.875O₄ (RE = Nd, Eu, Gd)体系的电子结构和磁性能. 结果表明随着稀土元素从Nd到Gd掺杂体系晶胞的晶格常数呈递减趋势. 磁性能依赖于稀土离子(RE³⁺)4f轨道未配对的电子数, 掺杂Eu和Gd能够提高钴铁氧体体系的磁矩, 主要因为它们3+价态离子具有较多未配对的4f电子, 因而对磁性能的影响较大. 然而Nd 的掺杂对体系磁性能的影响很小, 这是由于它的离子半径较大, 导致晶格发生畸变.     

Effect of aluminum substitution on the structural and magnetic properties of cobalt ferrite synthesized by sol-gel auto combustion process

Aluminum substituted cobalt ferrite powders (CoFe_2−xAl_xO₄) with varying composition from 0.0 to 1.0 in the step of 0.2 have been obtained by sol-gel auto combustion technique using citric acid as a fuel. The metal nitrate to fuel ratio was maintained 1:4 throughout the synthesis of CoFe_2−xAl_xO₄. The thermal analysis of as prepared samples is done by TGA technique. The compositional stoichiometry of the prepared samples is confirmed by Energy dispersive X-ray analysis technique. Single phase cubic spinel structure and nano phase structure of the synthesized powders were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallite size of 16-26 nm was obtained using Scherrer formula. SEM analysis shows the formation of uniform grain growth. The grain size obtained from SEM results is of the order of 30 nm. Maximum specific surface area was observed to be of the order of 52 m²/gm. The highest value of saturation magnetization and coercivity was observed for pure cobalt ferrite sample and it decreases as the aluminum content x increases. A strong co-relation between the saturation magnetization and aluminum content was observed. The decrease in magnetic properties is due to the substitution of aluminum ions in place of Fe³⁺.     

Effects of Zr substitution on structural,morphological, and magnetic properties of bismuth iron oxide phases

The present study involves co-precipitation method to grow un-doped and Zr-doped bismuth iron oxide with x_(Zr)=0.10–0.30. The molar solutions of ferric chloride(FeCl_3), zirconyle chloride(ZrOCl_2), and bismuth chloride(BiCl_3) are prepared in distilled water, and are allowed to react with sodium hydroxide(Na OH). The synthesized powders are then converted into pellets, which are sintered at 500℃ for two hours in a muffle furnace. X-ray diffraction(XRD) shows multi-phase formation in un-doped and Zr doped samples. Scanning electron microscope(SEM) depicts layered structure at low Zr concentration x_(Zr)= 0.10, while uniform surface with smaller grains and voids is observed at x_(Zr)= 0.20, but at x_(Zr)= 0.30, cracks and voids become prominent. The ferromagnetic nature of the un-doped sample is observed by vibrating sample magnetometer(VSM), while paramagnetic behavior appears due to Zr doping. The ferromagnetism in un-doped sample is lost by Zr doping, which is due to the formation of additional Fe–O–Zr bonds that induce paramagnetic behavior.     

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