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.     

Magnetic properties of Yb Mo O and Gd Mo O from rare earth Mössbauer measurements

Using ¹⁷⁰Yb and ¹⁵⁵Gd M?ssbauer measurements down to ∼ 0.03 K, we have examined the semiconducting pyrochlore Yb₂Mo₂O₇ where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd₂Mo₂O₇ where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and ¹⁷²Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb₂Mo₂O₇ and modest in Gd₂Mo₂O₇. Magnetic irreversibilities occur at 17 K in Yb₂Mo₂O₇ and at 75 K in Gd₂Mo₂O₇ and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd₂Mo₂O₇, we observe the steady state Gd hyperfine populations at 0.027 K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic. Received 13 January 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: hodges@drecam.saclay.cea.fr     

Magnetic susceptibility and 119Sn Mössbauer spectroscopy studies of RAuSn compounds (R=La, Ce, Pr)

In this paper the results of bulk magnetic susceptibility measurements and ¹¹⁹Sn Mössbauer spectroscopy measurements of LaAuSn, CeAuSn and PrAuSn intermetallic compounds are presented. New phase transitions in CeAuSn and PrAuSn compounds have been found by both methods employed. Structural and electronic properties are discussed.     

Magnetic properties of the R1+eFe4B4 compounds (R = rare earth) from magnetization and Mössbauer measurements

The magnetic properties of rare earth-iron-boron alloys with composition R_1+eFe₄B₄ have been determined using Mössbauer and magnetization measurements. Magnetic ordering occurs at temperatures between 4.2 and 25 K for the compounds with R = Pr, Nd, Sm, Gd, Tb, Dy, Ho. The Curie temperature scales very well with the de Gennes factor for the heavy rare earth members of the series, while significant deviations are observed for the light rare earths indicating the presence of strong CEF effects. The absence of magnetic hyperfine splitting even at 4.2 K indicates that the Fe ion has a zero magnetic moment. This is confirmed by Mössbauer spectra in an applied magnetic field.     

Magnetic and151Eu mössbauer studies on EuTGa (T=Pd AND Pt) compounds

The compounds EuPdGa and EuPtGa show lattice volume anomaly indicating the abnormal valence state of Eu. in these compounds. Magnetization studies reveal that these compounds are magnetically ordered with a moment of 7 _B/f.u. at 5K. The Curie temperatures obtained from the low field ac susceptibility measurements are 38K for EuPdGa and 36K for EuPtGa.¹⁵¹Eu Mössbauer studies at 300K gave large negative isomer shifts (relative to SmF₃) and show a hyperfine split pattern at 4.2K in both the compounds. These results suggest that Eu is in a divalent state in EuPdGa and EuPtGa.     

Mössbauer studies and magnetic properties of spinel lead ferrite

In the present communication, we have reported the synthesis of nanocrystalline lead ferrite (PbFe₂O₄) by citrate mediated autocombustion method. X-ray diffraction pattern reveals the single phase formation in cubic (spinel) structure. The particle size and the surface morphology of the samples are characterized by TEM and SEM analysis. Magnetic studies are carried out using vibrating sample magnetometer (VSM) shows a very high coercive field for the material. Mössbauer studies were performed to investigate the local symmetry i.e. Fe is in octahedral/tetrahedral site and the charge states of Fe ions.     

Mössbauer studies of heterobimetallic and heterotrimetallic compounds containing iron and tin

A series of ferrocene derivatives was prepared and studied by⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy, as well as by other techniques such as NMR and IR spectroscopies. These complexes can be divided into three types: mercurated, organotin derivatives of ferrocene, and bi- and trimetallic derivatives of 1,1-bis(diphenylphosphino)ferrocene. Iron did not show great variation in its Mössbauer parameters in the compounds, in spite of their diversity; tin, however, gave important Mössbauer data for the elucidation of bonding and structural features of the complexes.     

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.     

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 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.     

Mössbauer studies of baotite and bafertisite

The Mössbauer effect was used to study silicate minerals of baotite and bafertisite at 298 K and 95 K. Each spectrum of baotite at 298 K and 95 K consists of two doublets, and they are contributed from Fe²⁺ and Fe³⁺ in the octahedral Tisites, respectively. Each spectrum of bafertisite at 298 K and 95 K is composed of two doublets, and they are mainly caused by Fe²⁺ in the octahedral Fe(I) and Fe(II)sites, respectively. The average effective ionic radii of the Ti sites in baotite and the Fe(I) and Fe(II)sites in bafertisite were estimated based on the correlation of the isomer shifts with the average effective ionic radii in silicates, and they are 0.56 , 0.73 and 0.73 , respectively.     

Magnetic and Mössbauer studies of cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)6]·3H2O

Cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)₆]·3H₂O (cyclam=1,4,8,11-tetraazacyclotetradecane) was synthesized from the reaction of trans-[MnCl₂(cyclam)]Cl with K₃Fe(CN)₆. A linear chain structure consisting of alternating [Mn(cyclam)]³⁺ and [Fe(CN)₆]³⁻ units was indicated by the IR and Mössbauer spectra. The variable-temperature magnetization and Mössbauer measurements revealed that this complex exhibited a long-range ordering below 6.8 K. The magnetic behavior of the complex was based on intrachain ferromagnetic and interchain antiferromagnetic interactions.     

Magnetic and superconducting properties of Tl(Sr1.5R0.5)CaCu2O7−δ compounds

DC magnetic susceptibility and resistivity measurements have been performed on 14 Tl(Sr_1.5R_0.5)CaCu₂O_7−δ compounds with R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. All samples except the Ce-doped compound show superconducting phase transition temperature around 80–90 K. The rare-earth atoms behave as local moments above the superconducting transition temperature of these compounds. Mechanism of filling of holes in the CuO₂ plane can be employed to interpret the suppression or enhancement of superconductivity by rare-earth ions in Tl(Sr_1.5R_0.5)CaCu₂O_7−δ.     

Magnetic and crystallographic properties of substituted Pr2Fe14−xMxB compounds (M = Si,Ga, CrandCu)

Structural and magnetic properties of Pr₂Fe_14−xM_xB systems (M = Si, Ga, CrandCu) are investigated. These compounds crystallize in a tetragonal system of P4₂/mnm-type for a Si content up to x = 2, Cr content up to x = 3 and for Ga and Cu concentration up to x = 1. The Curie temperature increases when Fe is substituted by Si, Ga and Cu, decreases when Fe is replaced by Cr. The saturation magnetization decreases with increasing content of an M element. The rate of the decrease is larger than that expected by a simple dilution model. The influence of M atoms on the anisotropy field is discussed.     

Magnetic and Mössbauer spectral studies of nano crystalline cobalt substituted magnesium ferrites (MgxCo1 − xFe2O4)

The electronic structure of the heme unit of deoxyhemoglobin including the proximal imidazole has been studied using the first-principles Hartree-Fock procedure. Our results for the ^57mFe isomer shift and asymmetry parameter are in very good agreement with the values obtained from Mössbauer spectroscopy measurements. The ^57mFe nuclear quadrupole coupling constant is smaller than the experimental result and possible ways to improve the agreement in the future are discussed. Improved analysis of the Mössbauer data, removing some approximations made for deriving the magnetic hyperfine tensor for the ^57mFe nucleus, is suggested to allow quantitative comparison with our results in the future.     

Superconductivity of LaMCuO system (MBa,Sr and Ca

Superconductivity of the compounds of LaMCuO system with K₂NiF₄ type structure has been studied. For the sintered compounds with MBa, Sr and Ca, the highest onset transition temperatures, T_ci, estimated from resistivity measurement are about 36.9K, 43.0K and 23.5K, respectively and the highest temperatures where the resistivity vanishes, T_cf, are about 27.8K, 34.0K and 15.5K, respectively. Almost complete Meissner effect has been confirmed by low frequency ac susceptibility measurement. Crystals of the compounds with MBa and Sr have been prepared. As the result of the preliminary experiment for a crystal with Ba, it is found that T_cf of the crystal is higher than any one of the sintered specimens with MBa, while the T_ci of the crystal is nearly the same as the highest one of the sintered specimens.     

Mössbauer spectral studies of di- and triorganotin(IV) histidinylleucinates

Some new di- and triorganotin(IV) derivatives of the formulae, R₂SnL, where R =Me, Ph, and n-Oct, and L is the dianion of histidinylleucine (H₂L abbreviated as H₂(His-Leu)) and R′₃ SnHL, where R^′?= Me and Ph, HL = monoanion of histidinylleucine, have been synthesized. The bonding and coordination behaviour in these derivatives are discussed on the basis of FT-IR and ¹¹⁹Sn Mössbauer spectroscopic studies. The ¹¹⁹Sn Mössbauer studies, together with the IR data suggest that the ligand in R₂Sn(His-Leu) acts as dianionic tridentate coordinating through C(O)O^???, –NH₂ at axial positions and N_peptide at equatorial position while in case of R′₃Sn(HHis ? Leu) the ligand acts as a monoanionic bidentate coordinating through C(O)O^??? and –NH₂ giving a distorted trigonal–bipyramidal environment around tin.