Hyperfine interactions in metal extracted from ordinary chondrite Tsarev L5: A study using Mössbauer spectroscopy with high-velocity resolution

For the first time, a study of hyperfine interactions in metal grains extracted from ordinary chondrite Tsarev L5 was done using Mössbauer spectroscopy with high-velocity resolution. Three magnetic (sextets) and one paramagnetic (singlet) components were revealed in the Mössbauer spectrum of extracted metal. The evaluated values of the magnetic hyperfine field were 332.5, 335.4 and 347.2 kOe. On the basis of Mössbauer parameters and metallographic data, the magnetic components were related to the α-Fe(Ni, Co), α′-Fe(Ni, Co) and α₂-Fe(Ni, Co) phases of Fe(Ni, Co) alloy, while the paramagnetic singlet was related to the γ-Fe(Ni, Co) phase.     

Hydrothermal-induced oriented growth of Fe–Co alloy and Sm-substituted magnetite nanowire composites

Fe–Co alloy and Sm³⁺-substituted magnetite nanowire composites (Co_xFe_1−x/Co_yFe_1−ySm_zFe_2−zO₄) have been synthesized via a hydrothermal method without using surfactants or templates. The effects of substitution on structure and morphology were investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy (TEM). The TEM image shows that the average diameter of the magnetite nanowires is about 40 nm and the length is several micrometers. The z=0.1 composite shows relatively high saturation magnetization (92.3 emu/g) detected by a vibrating sample magnetometer. The possible growth mechanism of the nanowires is discussed on the basis of the crystal structure of the materials. From the perspective of thermodynamics, we explain the postulated mechanism of the hydrothermal reaction.     

Exhibition of High- and Low-spin States of the High-temperature Fcc Phase in Nanoparticles of Fe,Fe-rich and Co-rich Alloys

The results of combined X-ray and Mössbauer studies of structure and local magnetic ordering in massive substances Fe, Fe–Ni, Fe–Mn, Fe–Ni–Mn, Fe–Pt, Fe–Co and aerosol nanoparticles produced by their evaporation in rare Ar atmosphere are discussed. This technique provides a stochiometric composition of alloys in nanoparticles. The smallest (5–8 nm) particles for all alloys containing Fe 60–65% are shown to have a bcc structure whereas with doubling a size the particles acquire a fcc structure. This is explained by the fact that by cooling the particles in the course of preparation they quickly reach a state close to the equilibrium and, according to the constitution diagram, must decompose into two phases. Such decomposition in massive alloys was never observed at temperatures below 300°C because of diffusive difficulties. It is found that as-fresh aerosol particles are covered with an X-ray amorphous oxide shell, which is displayed in the room temperature Mössbauer spectra as a superparamagnetic doublet and is transformed into sextet at lower temperatures. An availability of the oxide shell has no practical influence on the particles structure. The obtained Mössbauer spectra are considered with the model suggested by R.J. Weiss in 1963, on existence of two-spin states in the high-temperature fcc modification of Fe and its alloys. Both states coexist, moreover, in the Mössbauer spectra the ferromagnetic state dominates at high temperature and anti-ferromagnetic one at low temperature. The ferromagnetic state manifests itself as a remnant of the frozen magnetic ordering of the high-temperature fcc modification in the resulting bcc structure, whereas the anti-ferromagnetic state is related to some fcc fraction retained under the particles quenching.     

Mössbauer study of Na0.82Co0.99Fe0.01O2

We studied by Mössbauer spectroscopy the Na_0.82CoO₂ compound using 1% ⁵⁷Fe as a local probe which substitutes for the Co ions. Mössbauer spectra at T=300 K revealed two sites which correspond to Fe³⁺ and Fe⁴⁺. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co⁺³, Co⁺⁴ ions and ion ordering of Na(1) and Na(2). Below T=10 K part of the spectrum area, corresponding to Fe⁴⁺ and all of Fe³⁺, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation.     

Synthesis and characterization of the xZnO-(1−x)α-Fe2O3 nanoparticles system

The xZnO-(1−x)α-Fe₂O₃ nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 h. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. The Rietveld structure of the XRD spectra yielded the dependence of the particle size and lattice constant on the amount x of Zn substitutions and as function of the ball milling time. The x=0.1 XRD spectra are consistent with line broadening as Zn substitutes Fe in the hematite structure and the appearance of the zinc ferrite phase at milling times longer than 4 h. Similar results were obtained for x=0.3, while for x=0.5 the zinc ferrite phase occurred at 2 h and entirely dominated the spectrum at 24 h milling time. The Mössbauer spectra corresponding to x=0.1 exhibit line broadening as the ball milling time increases, in agreement with the model of local atomic environment. Because of this reason, the Mössbauer spectrum for 12 h of milling had to be fitted with two sextets. For x=0.3 and 12 milling hours, the Mössbauer spectrum reveals the occurrence of a quadrupole-split doublet, with the hyperfine parameters characteristic to zinc ferrite, ZnFe₂O₄. This doublet clearly dominates the Mössbauer spectrum for x=0.5 and 24 h of milling, demonstrating that the entire system of nanoparticles consists finally of zinc ferrite. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications.     

Properties of Fe–Ga based powders prepared by mechanical alloying

Alloys of Fe–Ga with starting compositions of 17, 19, 21, 23, and 25 at% Ga and Fe₈₁Ga₁₇Z₂ (Z=Si, Sn) have been prepared by mechanical alloying. Samples were milled in a SPEX Model 8000 mill with a ball to sample weight ratio of about 4:1. Phase formation as a function of milling time has been investigated for the 19 at% Ga sample and suggests that milling times of 12 h produce fully alloyed samples. Alloys have been studied by electron microprobe, X-ray diffraction, vibrating sample magnetometery and ⁵⁷Fe Mössbauer effect spectroscopy. Fully milled powders have measured compositions of Fe_100−xGa_x with x=15.7, 17.0, 19.0, 22.4, and 24.0 and Fe_83.1Ga_15.2Z_1.7 (for both Z=Si and Sn). X-ray diffraction showed the presence of a disordered bcc phase with no indication of an ordered D0₃ phase. However, the latter is difficult to observe with X-ray diffraction because of the low intensity of the fcc superlattice peaks. A bimodal Fe hyperfine field distribution as obtained from Mössbauer effect spectra indicated the presence of two discrete Fe environments. The results suggested a lower degree of Ga clustering than has been previously observed in Fe–Ga alloys, of similar composition, prepared by melt spinning. The microstructure is similar to that of Fe–Ga thin films prepared by combinatorial sputtering. Some samples have also been studied after annealing at 800 °C for 8 h. No changes were observed in X-ray diffraction patterns after annealing. However, Mössbauer effect studies show the formation of D0₃ and L1₂ order in annealed samples analogous to the phases observed in melt spun ribbons of similar composition.     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95(过渡金属元素T=Mn，Fe，Co，B，Al，Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现，不同金属T替代Fe，Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95，合金具有相同的MgCu₂型立方Laves相结构；Al，Ga替代使Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴，即自旋重取向，B，Mn，Co替代未使易磁化轴发生明显转动；Al，Ga元素替代使超精细场H_hf略有下降，B，Mn替代对超精细场H_hf的影响不大，而Co元素替代使超精细场H_hf有较大增加；所有元素替代使同质异能移IS有所增加；B，Al，Ga和Mn替代使四极劈裂Q_s增加，而Co替代使四极劈裂Q_s下降. 关键词： 立方Laves相 自旋重取向 穆斯堡尔谱     

Spectral studies of Co substituted Ni-Zn ferrites

The spinel ferrites Zn_0.35Ni_0.65−xCo_xFe₂O₄, 0≤x≤1, have been prepared using the standard ceramic technique. Room temperature Mössbauer, X-ray and infrared IR spectra were used for carrying out this study. X-ray patterns reveal that all the samples have single-phase cubic spinel structure. The Mössbauer spectra of the samples show a paramagnetic phase for x=0 and a six-line magnetic pattern and a central paramagnetic phase for x≥0.1. They are analyzed and attributed to two magnetic subpatterns and two quadrupole doublets due to Fe³⁺ ions at the tetrahedral A-sites and octahedral B-sites. Four absorption bands are observed in IR spectra. They confirm the spinel structure of the samples and existence of Fe³⁺ ions in the sample sublattices. The deduced hyperfine interactions, lattice parameters, absorption band positions and intensities and force constant are found to be dependent on the substitution factor x, where the cation distribution is estimated. The hyperfine magnetic fields, magnetization and lattice resonant frequency are found to be dependent on the interionic distance.     

Preparation,characterization, magnetic property,and Mössbauer spectra of the β-FeOOH nanoparticles modified by nonionic surfactant

β-FeOOH nanoparticles have been prepared in a microemulsion system with nonionic surfactant polyoxyethylene(4)nonylphenylether CH₃(CH₂)₈C₆H₄O(CH₂OCH₂)₄H. The powder X-ray diffraction, infrared spectra, and transmission electron microscopic images indicate that the products are 20–30 nm length nanorods with a crystal structure belonging to monoclinic β-FeOOH and lattice parameters of a=0.9981, b=0.2948, c=1.0485 nm and β=92.26°. The size and shapes of β-FeOOH nanoparticles can be manipulated by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperatures. The ⁵⁷Fe Mössbauer spectra show that the magnetic structure transforms below 150 K and two kinds of Fe–O octahedra exist in the lattice of the modified β-FeOOH nanoparticles. The numbers of each kind of Fe–O octahedra are not the same at room temperature or at low temperatures.     

Time integral and time differential Mössbauer measurements on [57Co/Mn(bipy)3](PF6)2

The Mössbauer emission spectra of nucleogenic iron(II) complexes with a low spin (LS) ground state show two metastable iron(II) high spin (HS) states at low temperatures. In order to identify these metastable HS states, the compound [⁵⁷Co/Mn(bipyridine)₃](PF₆)₂ has been studied by time differential Mössbauer emission spectroscopy (TDMES) and optical lifetime measurements of excited electronic states in the corresponding Fe-doped Mn compound. The lifetime of one of the HS states of the nucleogenic iron(II) determined by TDMES has been measured to be the same as the lifetime of the laser-excited iron(II) electronic state.     

Mössbauer study of cobalt ferrite nanocrystals substituted with rare-earth Y ions

Mössbauer spectroscopy is used to characterize the crystallite size and structure of CoFe_2−xY_xO₄ (x=0, 0.1, 0.3, 0.5) ferrite nanocrystallites synthesized by the sol-gel auto-combustion method. The effect of the substitution of Fe³⁺ ions by Y³⁺ ions on the structure of cobalt ferrite nanocrystallites is investigated. The Mössbauer spectra showed two sets of six-line hyperfine patterns for all the samples, indicating the presence of Fe in both A and B-sites. On increasing the concentration of doped Y, the hyperfine field strength and the isomer shift first increase and then decrease, whereas the quadrupole splitting continuously increases. The superparamagnetism was observed for all the samples and the change of ratio of the superparamagnetism component reflects the size of crystal grain.     

Effect of Mn on the magnetic properties of Fe3B/Nd2Fe14B nanocomposites

The magnetic properties of Nd_4.5Fe_77−xMn_xB_18.5 (x=0, 1 and 2) nanocomposites prepared by the crystallization of amorphous precursors were investigated. Addition of Mn is found to decrease the crystallization temperature of the amorphous ribbons. The intrinsic coercivity _iH_c and maximum energy product (BH)_max increase from 2.6 kOe and 9.1 MGOe for x=0 to 3.1 kOe and 10.3 MGOe for x=1, respectively, and the remanence ratio M_r/M_s increases from 0.70 to 0.72. The effect of Mn on Curie temperature T_C and the thermal stability of M_r and _iH_c were also studied. ⁵⁷Fe Mössbauer spectra have been recorded for x=0, 1 and 2 ribbons at room temperature and site preference of the Mn atoms in Fe₃B and Nd₂Fe₁₄B phases is discussed using the Mössbauer spectroscopy.     

Studies on Structural, Magnetic and Thermal Properties of xFe2TiO4-(1−x)Fe3O4 (0≤x≤1) Pseudo-binary System

The xFe₂TiO₄-(1−x)Fe₃O₄ pseudo-binary systems (0≤x≤1) of ulvöspinel component were synthesized by solid-state reaction between ulvöspinel Fe₂TiO₄ precursors and commercial Fe₃O₄ powders in stochiometric proportions. Crystalline structures were determined by X-ray powder diffraction (XRD) and it was found that the as-obtained titanomagnetites maintain an inverse spinel structure. The lattice parameter a of synthesized titanomagnetite increases linearly with the increase in the ulvöspinel component. ⁵⁷Fe room temperature Mössbauer spectra were employed to evaluate the magnetic properties and cation distribution. The hyperfine magnetic field is observed to decrease with increasing Fe₂TiO₄ component. The fraction of Fe²⁺ in both tetrahedral and octahedral sites increases with the increase in Ti⁴⁺ content, due to the substitution and reduction of Fe³⁺ by Ti⁴⁺ that maintains the charge balance in the spinel structure. For x in the range of 0 ≤x≤0.4, the solid solution is ferrimagnetic at room temperature. However, it shows weak ferrimagnetic and paramagnetic behavior for x in the range of 0.4<x≤0.7. When x>0.70, it only shows paramagnetic behavior, with the appearance of quadrupole doublets in the Mössbauer spectra. Simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) studies showed that magnetite is not stable, and thermal decomposition of magnetite occurs with weight losses accompanying with exothermic processes under heat treatment in inert atmosphere.     

Magnetic response of microbially synthesized transition metal- and lanthanide-substituted nano-sized magnetites

The magnetic susceptibility (κ_RT) and saturation magnetization (M_S) of microbially synthesized magnetites were systematically examined. Transition metal (Cr, Mn, Co, Ni and Zn)- and lanthanide (Nd, Gd, Tb, Ho and Er)-substituted magnetites were microbially synthesized by the incubation of transition metal (TM)- and lanthanide (L)-mixed magnetite precursors with either thermophilic (TOR-39) or psychrotolerant (PV-4) metal-reducing bacteria (MRB). Zinc incorporated congruently into both the precursor and substituted magnetite, while Ni and Er predominantly did not. Microbially synthesized Mn- and Zn-substituted magnetites had higher κ_RT than pure biomagnetite depending on bacterial species and they exhibited a maximum κ_RT at 0.2 cationic mole fraction (CMF). Other TMs’ substitution linearly decreased the κ_RT with increasing substitution amount. Based on the M_S values of TM- and L-substituted magnetite at 0.1 and 0.02 CMF, respectively, Zn (90.7 emu/g for TOR-39 and 93.2 emu/g for PV-4)- and Mn (88.3 emu/g by PV-4)-substituted magnetite exhibited higher M_S than standard chemical magnetite (84.7 emu/g) or pure biomagnetite without metal substitution (76.6 emu/g for TOR-39 and 80.3 emu/g for PV-4). Lanthanides tended to decrease M_S, with Gd- and Ho-substituted magnetites having the highest magnetization. The higher magnetization of microbially synthesized TM-substituted magnetites by the psychrotroph, PV-4 may be explained by the magnetite formation taking place at low temperatures slowing mechanics, which may alter the magnetic properties compared to the thermophile, through suppression of the random distribution of substituted cations.     

Mössbauer and magnetic studies of orthorhombic FeSiO3

Magnetic properties of orthoferrosilite FeSiO₃ have been examined using susceptibility, magnetization measurements and Mössbauer spectroscopy. From magnetic and Mössbauer measurements, one obtains close values of the magnetic ordering temperature, T_N=39±1 K and T_N=41±1 K, respectively. The magnetic order is characterized by strong ferromagnetic coupling of Fe²⁺ moments within the ribbons and a weak antiferromagnetic coupling of the moments between adjacent ribbons. The 4.2 K Mössbauer spectra can be fitted with two different hyperfine magnetic fields H_hf=68 kOe and H_hf=314 kOe which can be assigned to Fe²⁺ in the octahedrally coordinated M1 and M2 sites, respectively, of the FeSiO₃ structure.     

Influence of aluminum doping in Li–Co–Ti ferrite

The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe³⁺ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄.     

Anti-Invar properties and magnetic order in fcc Fe-Ni-C alloy

Anti-Invar effect was revealed in the fcc Fe-25.3%Ni-0.73%C (wt%) alloy, which demonstrates high values of thermal expansion coefficient (TEC) (15-21)×10⁻⁶ K⁻¹ accompanied by almost temperature-insensitive behavior in temperature range of 122-525 K. Alloying with carbon considerably expanded the low temperature range of anti-Invar behavior in fcc Fe-Ni-based alloy. The Curie temperature of the alloy T_C=195 K was determined on measurements of temperature dependences of magnetic susceptibility and saturation magnetization. The Mössbauer and small-angle neutron scattering (SANS) experiments on the fcc Fe-25.3%Ni-(0.73-0.78)%C alloys with the varying temperatures below and above the Curie point and in external magnetic field of 1.5-5 T were conducted. Low value of the Debye temperature Θ_D=180 K was estimated using the temperature dependence of the integral intensity of Mössbauer spectra for specified temperature range. The inequality B_eff=(0.7-0.9)B_ext was obtained in external field Mössbauer measurement that points to antiferromagnetically coupled Fe atoms, which have a tendency to align their spins perpendicular to B_ext. Nano length scale magnetic inhomogeneities nearby and far above T_C were revealed, which assumed that it is caused by mixed antiferromagnetically and ferromagnetically coupled Fe atom spins. The anti-Invar behavior of Fe-Ni-C alloy is explained in terms of evolution of magnetic order with changing temperature resulting from thermally varied interspin interaction and decreasing stiffness of interatomic bond.     

Structural, electronic and magnetic properties of Mn, Co, Ni in Gen for (n=1-13)

The structural, electronic and magnetic properties of TMGe_n (TM=Mn, Co, Ni; n=1-13) have been investigated using spin polarized density functional theory. The transition metal (TM) atom prefers to occupy surface positions for n<9 and endohedral positions for n≥9. The critical size of the cluster to form endohedral complexes is at n=9, 10 and 11 for Mn, Co and Ni respectively. The binding energy of TMGe_n clusters increases with increase in cluster size. The Ni doped Ge_n clusters have shown higher stability as compared to Mn and Co doped Ge_n clusters. The HOMO-LUMO gap for spin up and down electronic states of Ge_n clusters is found to change significantly on TM doping. The magnetic moment in TMGe_n is introduced due to the presence of TM. The magnetic moment is mainly localized at the TM site and neighbouring Ge atoms. The magnetic moment is quenched in NiGe_n clusters for all n except for n=2, 4 and 8.     

A Mössbauer effect and X-ray diffraction study of Fe–Ga–Al thin films prepared by combinatorial sputtering

A combinatorial thin film library of the composition Fe_100−yGa_y−xAl_x was prepared by magnetron sputtering. The composition was determined by electron microprobe and showed that the Fe content was reasonably constant across the library and the Al to Ga ratio varied linearly with position. The crystallographic structure was determined with X-ray diffraction and found to be bcc. ⁵⁷Fe Mössbauer spectroscopy was used to investigate short-range order within the film. It was shown that non-magnetic atoms tend to cluster in these alloys, but that the substitution of Al for Ga reduced this tendency. This behavior may be, at least partially, responsible for the decrease in saturation magnetostriction between Fe–Ga and Fe–Al alloys.