Mössbauer study on characterization of Co[Fe(CN)5NH3 \cdot x H2O

The electronic states of Fe atoms in Co[Fe(CN)₅NH₃ H₂O were studied by means of ⁵⁷Fe Mössbauer spectroscopy. The Mössbauer spectra of Co[Fe(CN)₅NH₃ 6H₂O show the coexistence of mixed valences for the Fe atoms and a magnetic relaxation at 4 K. When water molecules were removed, electron transfer from Co to Fe occurred.     

Microwave absorption and Mössbauer studies of Fe3O4 nanoparticles

Materials consisting of nanometer-sized magnetic particles are currently the subject of intensive research activities. Especially, much attention has been paid to their promising features for microwave magnetic properties. Well dispersed Fe₃O₄ nanoparticles of 30 nm have been synthesized by oxidization method with NaNO₂, and the microwave magnetic properties of the composites have been studied. The real and imaginary part of relative permittivity remained low and nearly constant in the region of 0.1–18 GHz, respectively. As a result, the resin composites having a thickness of 2.0–3.2 mm, and containing 20 vol% Fe₃O₄ in the form of nanoparticles with an average diameter of 30 nm, exhibited excellent electromagnetic wave absorption properties in the frequency range of 4.5–12.0 GHz.     

Mössbauer and PAC studies of nanocrystalline Fe

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using⁵⁷Co/Fe Mössbauer and¹¹¹In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.     

Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.     

Magnetic and 57Fe Mössbauer studies of collinear spin rotation in Ho2Fe14B

Magnetic properties of Ho₂Fe₁₄B compounds have been studied by the ⁵⁷Fe Mössbauer effect and magnetization measurements. The axes of easy and hard magnetizations lie along the [001] and the [100] directions in the tetragonal structure, respectively, above T_sc = 58 K. From the comparison of the Mössbauer results with the magnetization measurements, it became clear that the Fe and the Ho moments tilt collinearly from the c-axis to the [110] direction throughout the temperature range of 4.2–58 K, and the canting angle reaches to 22° at 4.2 K. The Mössbauer spectra are consistently resolved with six subspectra above T_sc and with twelve below T_sc, together with reasonable site-assignments. We have estimated the mean Ho moment at 10.0μ_B, using the mean Fe moment of 2.3μ_B derived from the average hyperfine field or using the magnetization of Y₂Fe₁₄B as the Fe-sublattice magnetization of Ho₂Fe₁₄B.     

Magnetic properties of nanoparticles of Prussian blue-based molecular magnets M 3[Cr(CN)6]2⋅zH2O (M=Fe, Co, and Ni)

The nanoparticles of Prussian blue-based molecular magnets, M ₃[Cr(CN)₆]₂?zH₂O (where M=Fe, Co, and Ni), prepared by a slow addition (drop by drop) of chemicals using the co-precipitation method, are investigated by means of X-ray diffraction, infra red spectroscopy and dc magnetization measurement techniques. The formation of nanoparticles has been confirmed by scanning electron microscopy, whereas the characteristic peak, observed in the range of 1900–2300 cm^?1 in the infrared spectra, corresponds to the CN stretching frequency of $\mbox{Cr}^{\mathrm{+III}}$ –CN– $M^{\mathrm{+II}}$ , and confirms the formation of Prussian blue compounds. The results, derived from the Rietveld refinement of X-ray diffraction patterns, reveal that all samples are nanocrystalline in nature with a face-centered cubic crystal structure of space group Fm3m. The particle size and the lattice constants decrease with an increasing atomic number of the transition metals (M=Fe, Co and Ni). The magnetization data show a magnetically ordered state of all nanoparticle samples with a low coercivity (except for the Fe₃[Cr(CN)₆]₂?zH₂O) as well as the remanent magnetization. In addition, by varying M with Fe, Co and Ni, the magnetic ordering temperature increases from ～12 to ～28 K, whereas the maximum magnetization and the coercive field decrease from ～14 to ～4.5 μ_B/f.u. and ～554 to ～22 Oe, respectively. The observed magnetization behavior has been discussed in terms of the structural changes due to the decreasing particle size as well as the varying nature of the metal ions.     

Magnetization and Mössbauer studies of 57Fe doped SrCoO3

⁵⁷Fe (1%) doped SrCoO₃ obtained by high-pressure method, has been investigated by magnetization and Mössbauer spectroscopy studies (MS) in the temperature range 4.2 K to 300 K. The ferromagnetic ordering temperature T _C obtained is 272(2) K. Isothermal magnetization curves have been measured at various temperatures, from which the saturation moments (M _sat) have been deduced. The ⁵⁷Fe MS spectra display standard six-line patterns with an isomer shift typical of Fe^3?+? and a very small quadrupole splitting (QS = 0.14(1) mm/s above T _C). The magnetic hyperfine field at 4.2 K is 276(1) kOe. The temperature dependencies of the iron hyperfine field and M _sat (1.83 µ _B at 5 K) are almost identical. This shows that the Fe^3?+? is replacing Co^4?+?, both of the same electronic configuration. They also interact similarly, namely the Fe–Co exchange is almost identical to the Co–Co exchange.     

Mössbauer spectroscopy and magnetic studies of orientated textured Fe3O4 ferrofluid

Nano scale magnetite based ferrofluid is synthesized by chemical co pre cipitation technique and stabilized with oleic acid. Magnetization and viscosity measurements were used to optimize for texturing purpose. The freeze-textured ferrofluid in two configurations, namely, (1) field texture system (FTS) and (2) zero field texture system (ZTS) are investigated by magnetization measurements at 298 K and Mössbauer spectroscopy measurements at 77 and 298 K. These results are analysed on the basis of the contributions from collective superparamagnetic reversal and the strength of the inter particle interactions.     

Mössbauer studies and magnetic properties of Ln2SrCu2O6 compounds

Mössbauer and magnetic susceptibility measurements were used to study the magnetic properties of Ln_1.9Sr_1.1Cu₂O₆ (Ln=Pr,Nd) and La₂SrCu₂O₆ materials. These compounds were prepared by solid-state reaction and crystallize in a tetragonal structure, space group I4/mmm with two formula units per unit cell. There is only one crystallographic site for Cu atoms, which form a double layer of CuO₅ pyramids. These compounds are not superconducting, but we show, using Mössbauer spectroscopy (MS) on iron doped samples and susceptibility measurements, that the Cu planes order antiferromagnetically. The hyperfine fields on iron nuclei at 4.2 K extend from 472 kOe for La₂SrCu₂O₆ to 501 kOe for Nd_1.9Sr_1.1Cu₂O₆. The ordering temperaturesT _N are: R20, 190, and 250 K for Ln=La, Pr and Nd, respectively.     

Mössbauer spectroscopic study on spin crossover coordination polymer Fe(3-Clpy)2[Pd(CN)4]

⁵⁷Fe Mössbauer spectroscopic results on the alternatively prepared spin crossover coordination polymer Fe(3-Clpy)₂Pd(CN)₄ sample I agree with those of SQUID data. Mössbauer specrum at RT shows two diffrent doublets which correspond to the HS1(inner doublet) and HS2(outer doublet). The intensity of the HS1 doublet decreases on cooling to 78 K at the expense of a new one featuring the LS singlet. Almost 100 % of HS1 change to LS singlet due to iron(II) ions coordinated by four N atoms of cyano groups and two N atoms of 3-Clpy ligand in the sample I. The SQUID data of the sample I prepared by a new direct contact method are different from those of the already reported Fe(3-Clpy)₂Pd(CN)₄ sample. The differences of the SQUID data are associated with particle size effects in molecule spin crossover samples.     

双金属化合物[Ni(en)2]3[Fe(CN)6]2·2H2O的变温穆斯堡尔谱研究

合成了一维绳梯链状双金属化合物[Ni(en)2]3[Fe(CN)6]2·2H2O,并对其变温穆斯堡尔谱进行了研究,结果表明该分子磁体中铁的电子态为低自旋Fe3 ,而大的四极分裂值(QS)表明此化合物的[Fe(CN)6]3-单元对称结构发生了形变,低温时出现的磁弛豫谱,给出了在该温度点附近出现铁磁耦合相互作用的信息。     

Magnetic and Mössbauer study of Mg0.9Mn0.1Cr x Fe2−x O4 ferrites

The ferrites Mg_0.9Mn_0.1Cr _x Fe_2?x O₄ ( The ferrites Mg_0.9Mn_0.1Cr _x Fe_2−x O₄ () were prepared using the conventional double sintering method. The XRD showed that the samples maintain a single spinel cubic phase. The M?ssbauer measurements were carried out at room and liquid nitrogen temperatures. From the area ratios of the A and B sites, it was found that the Fe cation population of the A and B sites decreases in proportion to Cr concentration. The contact hyperfine fields at the A and B sites were found to decrease with increasing Cr contents. This was found to be in approximate agreement with the results of magnetization measurement. The distributions of Mg and Mn cations versus Cr concentration were also determined using the M?ssbauer and magnetization results. The Curie temperatures were determined and found to agree with the reported values. As the Cr contents increases the relative magnetization, was found to increase at low temperatures and decreases at higher temperatures.     

Magnetic and Mössbauer studies of the superconductor Eu(Dy,Gd)Ba2Cu3O7−δ

The changes of the microstructures of bulk single-phase Eu_1–x Dy _x Ba₂Cu₃O_7– and Eu_1–y Gd _y Ba₂Cu₃O_7– superconductors due to (Dy, Gd)-doping were investigated by the Mössbauer effect. The pinning potentials of the samples were calculated by magnetization relaxation analysis. The interaction between the magnetic moment of magnetic rare-earth cations and flux lines in these samples was considered as a predominant pinning mechanism in highT _c superconductors in this paper.     

Magnetic and Mössbauer studies of the DyFe11Mo compound

A detailed magnetic and Mössbauer study focusing on intrinsic magnetic and anisotropy properties of the DyFe₁₁Mo compound is reported. The compound shows a spin reorientation phase transition at T_sr=220 K. Anomalies in physical properties such as saturation magnetization, AC-susceptibility and hyperfine field at T_sr were identified, analysed and are discussed in terms of the individual site anisotropy model.     

Diffusion of water in molecular magnet Cu(0.75)Mn(0.75)[Fe(CN)6]·7H2O

Here we report the dynamical behaviour of water in Prussian blue analogue (PBA) Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O molecular magnet in the temperature range 260-360 K as studied using the quasielastic neutron scattering technique. While significant quasielastic broadening is observed in the hydrated sample, no broadening was observed in the dehydrated one. Data analysis showed that the observed quasielastic broadening in Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O corresponds to the dynamics of the non-coordinated water molecules at the 32f site and the coordinated water molecules at the 24e site, existing in the cavities created by the absence of Fe(CN)(6) units. The non-coordinated water molecules at 8c interstitial sites do not contribute to the broadening, suggesting that they are immobile at least within the time window of the spectrometer used. Behaviour of the elastic incoherent structure factor is consistent with the model where the water molecules undergo translational diffusion localized within the cavity of 5.1 ?. While all the non-coordinated water molecules at the 32f site are dynamic over the entire range of temperatures, the coordinated ones at the 24e site become progressively dynamic with temperature. The water molecules were found to undergo hindered (~1.16 × 10(-5) cm(2) s(-1) at 300 K) diffusion compared to bulk water and the diffusivity followed Arrhenius behaviour within the measured temperature range with an activation energy of 1.26 kcal mol(-1).     

Magnetic properties and Mössbauer studies in Y1−x Gd x Fe2

Alloys of Y_1???x Gd _x Fe₂B _y (x = 0, 0.25, 0.5, 0.75 and 1; y = 0, 0.1, 0.15 and 0.2) have been prepared and investigated for structural and magnetic properties. The compounds with x = 0 and 1 are found to form in single phase with C15-type cubic Laves phase structure, while those with x = 0.25, 0.5 and 0.75 are observed to form with small quantities of secondary (Y,Gd)Fe₃ phase. The lattice parameters, Curie temperature and the average Fe hyperfine field are found to increase with increasing x. The Gd–Gd and Gd–Fe interactions are attributed to be the main reason for the enhancement of magnetic properties. Boron was found to stabilize the (Y,Gd)Fe₂ phase without affecting the magnetic properties.