Effect of formation conditions on the structure, morphology and magnetic properties of nanosized MIIFe 2III O4 ferrites (M = Mn, Co, Ni) and Fe2O3

A study was carried out on the conditions of formation of highly crystalline, superparamagnetic, nanosized oxides, M^II Fe ₂ ^III O₄ and γ-Fe₂O₃ (4.9–11.7 nm) by the thermal decomposition of complexes [MFe₂O(CH₃CO₂)₆(H₂O)₃] (M = Mn, Fe, Co, Ni) in tetraethylene glycol. The presence of surfactants leads to a decrease in the size and size distribution of the nanoparticles formed, while the use of microwave radiation significantly reduces the time for formation of the nanocrystalline oxides. The magnetic measurements showed ferrimagnetic ordering in the nanoparticles studied and their superparamagnetic behavior. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 323–329, September–October, 2007.     

Catalytic decomposition of hydrogen peroxide on fine particle ferrites and cobaltites

The kinetics of heterogeneous decomposition of hydrogen peroxide on fine particle ferrites, MFe₂O₄ and cobaltites, MCo₂O₄, where M=Mn, Fe, Co, Ni, Zn and Mg, have been investigated. The decomposition of H₂O₂ was found to be first order at low concentration (0·3%) and zero order at high concentration (30%) of H₂O₂. The catalytic activity of cobaltites on the decomposition of H₂O₂ is found to be better than ferrites. The observed catalytic behaviour of ferrites and cobaltites has been attributed to their fine particle nature, large surface area and electronic structure.     

Comparative investigation of CuFe2O4 nano and microstructures for structural,morphological, optical and magnetic properties

CuFe₂O₄ nanocrystals were synthesized by the sol–gel method (SGM) and microwave method (MM) by using sucrose as a fuel. The structural, morphological, optical and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM). The XRD results confirmed the formation of cubic phase CuFe₂O₄. The formation of CuFe₂O₄ nano and microstructures were confirmed by HR-SEM. Photoluminescence emissions were determined by PL spectra, respectively. The relatively high saturation magnetization (78.22 emu/g) of CuFe₂O₄-MM shows that it is ferromagnetic and low saturation magnetization (35.98 emu/g) of CuFe₂O₄O-SGM confirms the super paramagnetic behavior.     

Hydrostatic pressure driven spin,volume and band gap collapses in SmFeO3: a GGA + U study

The crystal structure, magnetic and electronic properties of SmFeO₃ under hydrostatic pressure have been studied by first-principles calculations within the generalized gradient approximation plus Hubbard U (GGA + U). The iso-structural phase transition with spin, volume and band gap collapses can be induced by a large enough hydrostatic pressure. The high-spin (HS) state of Fe³⁺, with the magnetic moment of ~4 μ_B, is retained at low pressure. The spin crossover occurs at a transition pressure (~68 GPa) with the magnetic moment of Fe³⁺ decreasing to ~1 μ_B in low-spin (LS) state. Meanwhile, the reductions of cell volume (by ~?5.43%) and band gap (from >2 eV to ~1.6 eV) of SmFeO₃ are obtained when the HS–LS transition happens. Finally, the critical pressure of HS–LS transition, magnetic and electronic properties are found to be Hubbard U dependent.     

Thermoanalytical Study of Cu-Mg-Zn Ferrites

Homogeneous solid solution oxalates of Fe²⁺, Cu²⁺, Mg²⁺ and Zn²⁺ metals were prepared by co-precipitation from respective metal acetate solutions with oxalic acid solution. The thermogravimetric (TG) analysis of co-precipitated oxalate complexes with general formula Mg_xCu_(0.50-x)Zn_0.50Fe₂(C₂O₄)₃·nH₂O (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50) were carried out by manual method in static air atmosphere. The total mass loss % and stepwise mass loss % values are in good agreement with theoretically calculated mass loss % values. The thermal decomposition of oxalate complexes occur at relatively lower temperatures (561 to 698 K). The lowering of decomposition temperatures may be attributed to earlier initiation of Fe²⁺ oxalate in oxalate complexes. At temperatures between 598–698 K the thermal decomposition of Cu-Mg-Zn-Fe solid solution oxalate complexes leads to formation of ferrites of spinel structure. After tampering at 873 and 1273 K, homogeneous ferrites arise, which is revealed from XRD studies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Anisotropy of the Hyperfine Field on 57Fe in Pure and Substituted Yttrium Iron Garnet

Using NMR, anisotropy of the hyperfine field on ⁵⁷Fe nuclei was measured in Y₃Fe₅O₁₂ with nonmagnetic, trivalent substitutions on d (Ga³⁺) and a (Y³⁺ - yttrium antisite defect) sites which are occupied by ferric ions in a pure, stoichiometric system. The measurements were performed by the spin-echo method at liquid helium temperature. Thorough analysis of the hyperfine field anisotropy on the ⁵⁷Fe nuclei in an ideal environment and in an environment where one of Fe³⁺ nearest cation neighbours is replaced by the nonmagnetic impurity is given. When the Fe³⁺ on which the NMR is measured is on the a site and the impurity is Ga³⁺(d), the results may be interpreted in terms of the superposition model. On the other hand, the results for Fe³⁺ on the d site and Y³⁺(a) are in clear disagreement with the predictions of this model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural,magnetic and dielectric properties of (Li1+, Al3+) co-doped Ni0.5Zn0.5Fe2O4 ferrite ceramics prepared by the sol-gel auto-combustion method

(Li¹⁺, Al³⁺) co-doped Ni_0.5Zn_0.5Fe₂O₄ ferrites, Ni_0.5-xZn_0.5-xLi_xAl_xFe₂O₄ (x = 0.000, 0.025, 0.050 and 0.100), were synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD), field emission scanning electronic microscope (FESEM), vibrating sample magnetometer (VSM) and LCR meter were used to investigate the structural, magnetic and dielectric properties. Results of XRD and SEM indicate that both doping amount and calcination temperature play significant roles in crystal structure and grain growth. Also, it can be observed that the saturation magnetization and the coercivity change in a noticeable manner. The Ni_0.475Zn_0.475Li_0.025Al_0.025Fe₂O₄ ferrite sintered at 1200 °C has a relatively low coercivity value (62.93 Oe) and the largest saturation magnetization (110.95 emu/g). Besides, dielectric behavior is also improved by Li¹⁺ and Al³⁺ co-doping.     

尖晶石结构MFe2O4(M=Ca,Mg,Cu,Zn)纳米晶粉末的制备和磁性能

采用新型氨基凝胶自燃法成功制备出尖晶石结构MFe₂O₄（M=Ca,Mg,Cu,Zn）纳米晶粉末。对合成粉体样品的物相、形貌和磁性能进行了详细的研究。经能量色散X射线谱分析确定了合成MFe₂O₄粉末的高纯度。系统地研究了所合成的MFe₂O₄纳米晶粉末的磁性能。所有样品的磁滞回线均较窄,表明了它们具有软磁的特征。经测试得出4种铁氧体的饱和磁化强度（M_s）分别为2.1,29.3,24.1和4.2 emu·g^-1;剩余磁化强度（M_r）分别为0.2,2.3,11.4和0.2 emu·g^-1。这4种铁氧体样品的M_r/M_s值均小于0.5。对CaFe₂O₄和MgFe₂O₄两种典型铁氧体的零场冷却和场冷磁性能作了详细的研究。其中CaFe₂O₄样品的磁化强度在75 K以下有不一致的变化趋势,这是由于其发生了磁相变。     

Hexaferrites and phase relations in the iron-rich part of the system Sr-La-Co-Fe-O

The iron rich part of the system was examined in the temperature range of 1200-1380 °C in air, with focus on the solid solutions of M-type hexaferrites. Samples of suitable compositions were studied by electronprobe microanalysis (EPMA). Substituted Sr-hexaferrites in the system Sr-La-Co-Fe-O do not follow the 1:1 substitution mechanism of La/Co in M-type ferrites. Due to the presence and limited Co²⁺-incorporation Fe³⁺-ions are reduced to Fe²⁺ within the crystal lattice to obtain charge balance. In all examined M-type ferrites divalent iron is formed, even at 1200 °C. The substitution principle Sr²⁺+Fe³⁺↔La³⁺+(Fe²⁺, Co²⁺) yields to the general substitution formula for the M-type hexaferrite Sr²⁺_1-xLa³⁺_xFe²⁺_x-yCo²⁺_yFe³⁺_12-xO¹⁹ (0≤x≤1 and 0≤y≤x). In addition Sr/La-perovskite_SS (_SS=solid solution), Co/Fe-spinel_SS, hematite and magnetite are formed. Sr-hexaferrite exhibits at 1200 °C a limited solid solution with small amounts of Fe²⁺ (SrFe₁₂O₁₉↔Sr_0.3La_0.7Co_0.5Fe²⁺_0.2Fe_11.3O₁₉). At 1300 and 1380 °C a continuous solid solution series of the M-type hexaferrite is stable. SrFe₁₂O₁₉ and LaCo_0.4Fe²⁺_0.6Fe₁₁O₁₉ are the end members at 1300 °C. The maximum Fe²⁺O content is about 13 mol% in the M-type ferrite at 1380 °C (LaCo_0.1Fe²⁺_0.9Fe₁₁O₁₉).     

Effect of Nd substitution on structural and electrical properties of nanocrystalline zinc ferrite

Polycrystalline soft ferrite samples with general formula ZnNd_xFe_2−xO₄ (where x=0, 0.01, 0.02 and 0.03) were synthesized by oxalate co-precipitation method. The samples were characterized by XRD and SEM techniques. The single phase cubic spinel structure of all the samples was confirmed by XRD. The lattice constant and grain size of the samples are found to decrease with increase in Nd³⁺ content. Room temperature DC resistivity of the Nd³⁺ substituted zinc ferrites is 10² times higher than that of zinc ferrite. The dielectric constant (ε′) and dielectric loss (tan δ) of all the samples were measured in the frequency range 20 Hz-1 MHz. The dielectric behaviour is attributed to the Maxwell-Wagner type interfacial polarization. The dielectric loss of the samples is found to decrease with increase in Nd³⁺ content. High resistivity and low dielectric loss makes these ferrites particularly suitable for high frequency applications.