Magnetism and hyperfine interactions in EuM2Ge2 and GdM2Ge2(M = Mn,Fe, Co,Ni, Cu)

X-ray, magnetic susceptibility and ¹⁵¹Eu, ¹⁵⁵Gd Mössbauer effect studies of EuM₂Ge₂ and GdM₂Ge₂ were performed. All compounds crystallize in the ThCr₂Si₂ body centered tetragonal structure. In all compounds, except those with M = Mn and in EuM₂Ge₂, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn₂Ge₂ the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behaviour is different from that in GdMn₂Ge₂, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Mössbauer studies of ¹⁵¹Eu and ¹⁵¹Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis (c-axis). It turns out that in the Eu compounds the easy axis of magnetization is close to the c-axis, while in the Gd compounds it is in the basal plane. In all systems, excluding those with Mn, the interatomic rare earth-rare earth distances have the dominant effect on the conduction electron charge density and polarization at the rare earth site and on the Curie point.     

151Eu and57Fe Mössbauer effect studies of magnetic interactions in europium transition element oxides solution

The solid state solutions of europium transition element oxides Eu (Fe0.8M0.2)O₃ (M=Sc,Cr,Mn,Co) are synthesized. The X-ray diffraction of the compound shows that all the compounds possess the perovskite structures. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The hyperfine magnetic field and non-axisymmetric electric field gradient are observed in the¹⁵¹Eu Mössbauer spectrum. The⁵⁷Fe Mössbauer spectrum shows that there are four components of hyperfine fields corresponding to four kinds of different neighbours of the Fe ion.     

Mössbauer effect study of Gd- and Eu-doped CaSO4

Mössbauer spectra have been taken of rare earth doped CaSO₄ using the¹⁵¹Eu and¹⁵⁵Gd transitions. Site assignments have been made to the five principal Gd³⁺ configurations principally on the basis of point charge calculations. We were unable to distingiush different Eu³⁺ sites and no conversion of Eu³⁺ to Eu²⁺ could be observed after prolonged x-irradiation.     

Mössbauer spectroscopic study on (Eu1−x Gd x )FeO3

Europium gadolinium ferrites (Eu_1?xGd_x)FeO₃ (X=0, 0.2, 0.4, 0.6, 0.8) are synthesized. The results of the X-ray diffraction show that all the compounds possess a perovskite structure. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The¹⁵¹Eu Mössbauer spectra are considered to be the pure quadrupole spectra. The results show that the isomer shift and the quadrupole splitting of the¹⁵¹Eu spectra vary with x. The hyperfine filed of the⁵⁷Fe Mössbauer spectrum depends on the unit-cell volume. The⁵⁷Fe spectra of the samples synthesised by the high-pressure and high-temperature mothod show a part of paramagnetic structure.     

Experimental search for laser-induced effects in <Superscript>151</Superscript>Eu and <Superscript>57</Superscript>Fe doped crystals

We studied the Mössbauer effect in ¹⁵¹Eu and ⁵⁷Fe doped crystals in the search for laser-induced effects caused by changes in the hyperfine interaction due to electronic excitation. The Mössbauer spectra observed in the presence of laser radiation demonstrated a notable change of the shape of the ¹⁵¹Eu spectrum and the appearance of an additional hyperfine pattern in the case of the ⁵⁷Fe Mössbauer resonance.     

M?ssbauer Spectroscopy: an elegant tool for the active sites identification and quantification in Pt-Sn-In based naphta reforming catalysts

The reaction of Ln(ClO₄)₃· nH₂O with triphenylphosphine oxide (TPPO) in methanol has led to the formation of [Ln(ClO₄)₂(tppo)₄]ClO₄·MeOH (Ln = Nd, Eu, Gd, Dy, Yb), in which the perchlorate anion acts as a symmetric bidentate. The emission spectra of Eu(III)-TPPO complexes, showing enhancement in the intensity due to the phenyl group, indicate an isotropic electron distribution for the nitrato complex [Eu(NO₃)₃(tppo)₂(EtOH)]. ¹⁵¹Eu and ¹⁵⁵Gd M?ssbauer spectra of the TPPO complexes also lead to the same conclusion.     

Studies of hyperfine interactions inRBa2(Cu1-x 57Fex)3O7-δ high-T c superconductors

Both⁵⁷Fe and¹⁵¹Eu Mössbauer resonances were used to study polycrystallineRBa₂Cu₃O_7-δ samples. The dependence of hyperfine interaction parameters on the oxygen deficiency δ is studied in detail with¹⁵¹Eu. For⁵⁷Fe spectra, a site assignment is proposed.     

151Eu Mössbauer studies on Eu1+x Ba2−x Cu3O7+δ oxide systems

Mössbauer parameters of¹⁵¹Eu in Eu_1+x Ba_2?x Cu₃O_7+δ have been studied as a function of temperature, forx=0.15 andx=0.25. The areas of the absorption spectra for the two samples are almost equal. This could mean that thef-Mössbauer factor for¹⁵¹Eu at the barium sites is much smaller than that for¹⁵¹Eu at the rare earth sites, i.e. we only observe the spectra of the latter sites. According to this, the fits of the spectra with a single quadrupolar pattern and with two quadrupolar patterns have given equivalent χ² values.     

Spin-reorientation in GdGa

We have determined the magnetic structure of the intermetallic compound GdGa by ¹⁵⁵Gd Mössbauer spectroscopy and neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure. It orders ferromagnetically at T _c ?=?190(2) K and then undergoes a spin reorientation at T _SR ?=?68(2) K. Between T _c and T _SR , the magnetic structure is characterized by ferromagnetic order of the Gd moments along the b-axis. On cooling below T _SR , the Gd 4c magnetic moments split into two groups (2:2). At 3.6 K, the Gd moment is 6.7(4) μ _B , and the Gd magnetic moments are in the bc-plane, canted by 84(3)° and 46(4)° with respect to the crystallographic b-axis. This splitting into two magnetically inequivalent sites is confirmed by our 5 K ¹⁵⁵Gd Mössbauer results.     

Nuclear excitation and isomer shifts in muonic atoms: (II). Model-independent parametrization and discussion

Excitation probabilities and isomer shifts for about 50 excited nuclear levels from muonic atoms of Sm, Gd, Eu, Tm, Yb, Ta, W, Re, Os, Ir, Pt, Hg, Tl, and Bi are discussed. The data for ¹⁵³Eu are used in comparison with isomer shifts from the Mössbauer technique to evaluate electron density differences in rare earth compounds. Mössbauer and muonic isomer shifts are sensitive to different moments of the change of the charge distribution. Therefore, from a comparison new information can be deduced. The results of the muonic isomer shifts are compared with calculations based on various nuclear models.     

Mössbauer studies of YBa2Cu3O7−δ-type high-T c superconductors

The local magnetic, electronic, and structural properties of (RE)Ba₂Cu₃O_7?δ supercondcutors (RE=Gd, Dy, and Eu) were studied by Mössbauer spectroscopy using the resonances of¹⁵⁵Gd,¹⁶¹Dy,¹⁵¹Eu, and⁵⁷Eu. In GdBa₂Cu₃O_7?δ, different magnetic ordering behaviors of the Gd sublattice are found for the orthorhombic (superconducting) and tetragonal (non-superconducting) phases. In DyBa₂Cu₃O_7?δ, the magnetic moments of the respective CEF ground states in the orthorhombic and tetragonal phases are derived from paramagnetic hyperfine splittings at 1.4 K. In both DyBa₂Cu₃O_7?δ and EuBa₂Cu₃O_7?δ, anomalies connected with the superconducting transitions in isomer shift, recoil-free fraction, and relaxation behavior were looked for, but not found. The electric-quadrupole splittings observed for both systems are discussed in connection with the lattice EFGs derived for the Gd system. In GdBa₂ (Cu_0.995Fe_0.005)₃O_7?δ, the local properties of the various Fe sites are investigated over a wide temperature range in both the orthorhombic and tetragonal phase. The magnetic ordering of the Gd sublattice in the orthorhombic phase and of the Cu(2) sublattice in the tetragonal phase, respectively, is monitored via the magnetic splittings at the various Fe sites. Possible assignments of Cu(1) and Cu(2) sites as well as different oxygen configurations around the substituted Fe ions are discussed.     

Comparative Mössbauer study of EuBa2 (Cu1-x 57Fe x )3O7-d and EuBa2Cu1-x 57Fe x )4O8 superconductors

Structural differences between the 1-2-3 type and 1-2-4 type high temperature superconductors were studied by comparing their¹⁵¹Eu and⁵⁷Fe Mössbauer spectra. The similarities between the corresponding Mössbauer parameters of Eu Mössbauer spectra of 1-2-3 and 1-2-4 compounds demonstrate that the Eu state can be considered to be identical in both perovskites. The changes in the Fe Mössbauer parameters of 1-2-4 type superconductor compared to those of 1-2-3 type compound can be associated with structural differences.     

Mössbauer studies of valence fluctuations

In the last ten years the Mössbauer technique has made a considerable contribution to the research of the phenomena of mixed valencies, valence instabilities, valence fluctuations and intermediate valencies of transition elements. The sensitivity of the hyperfine interaction parameters and in particular the isomer shift, to the valency of the Mössbauer ion, enabled the research of dynamics of valence fluctuations and the temperature, pressure and composition dependence of the ionic intermediate valence state. Studies of¹⁴⁹Sm,¹⁵²Sm and¹⁵³Eu in Sm_1?xR_xS contributed to the understanding of the outstanding insulator-metal phase transition that occurs in these systems. Studies of⁵⁷Fe and¹⁵¹Eu in mixed valent systems yield the charge fluctuation rates of the “hopping” mechanism, contributing to the conductivity in these systems. Studies of¹⁵¹Eu in EuRh₂, EuCu₂Si₂, EuPd₂Si₂, EuFe₄Al₈, and EuPd₆B₄ as a function of temperature and pressure reveal many aspects of the thermodynamics of intermediate valencies. Studies of systems like Eu_1?xLa_xRh₂, EuA_2?xB_x, EuA_5?xB_x reveal strong local environment dependence of the intermediate valency. Mössbauer spectra of¹⁶⁹Tm in TmSe,¹⁷⁰Yb in YbAl₃ and²³⁷Np in NpOs₂ also display phenomena associated with fluctuating valencies.     

57Fe,119Sn and151Eu Mössbauer study of EuBa2(Cu1−x−y 119Sn x 57Fe y )3O7−δ superconductor

¹⁵¹Eu,¹¹⁹Sn and⁵⁷Fe Mössbauer spectroscopy was used to study a EuBa₂(Cu_1?x?y Sn _x Fe _v )₃O_7?δ superconductor in which sites were replaced by all three Mössbauer isotopes in the same sample in order to get information about the site preferences and structural changes. We have found changes in the Mössbauer parameters of the⁵⁷Fe,¹¹⁹Sn and¹⁵¹Eu spectra compared to those recorded in the separately substituted EuBa₂Cu₃O_7?δ, EuBa₂(Cu_1?x Sn _x )₃O_7?δ, YBaCu_3?x Fe _x O_7?δ YBaCu_3?x Sn _x O_7?δ materials. These results can be interpreted as a consequence of the site preferences and the changes in the structure due to the presence of other additional substitutional elements.     

Magnetic order and hyperfine interactions in RFe6Al6 (R = rare earth)

The systems RFe₆Al₆(R = Y, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) crystallize in the tetragonal body centered I4/mmm structure. In striking contrast to the magnetic behaviour of RFe₄Al₈ (weakly coupled R and Fe sublattices, complicated magnetic structure, low T_c ~ 130 K), in the RFe₆Al₆ systems all magnetic sublattices order simultaneously at a relatively high temperature. The magnetization curves start with low values at low temperatures and rise to very high values at T_max ~ 230 K and then drop to 0 at T_c ~ 330 K. All samples show strong hysteresis effects at temperatures just below T_max. Mossbauer studies of ⁵⁷Fe in the (f) and (j) sites and ¹⁵¹Eu, ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er and ¹⁷⁰Yb in the (a) site yield all hyperfine interaction parameters and temperature dependence of the local magnetic moments. All Mossbauer and magnetization experimental results can be explained in a self consistent way with a simple molecular field model. The Fe in the (j) site plays the dominant role in its strong intrasublattice ferromagnetic exchange and its strong antiferromagnetic exchange with the rare earth site. The Fe in the (f) site have an antiferromagnetic intrasublattice exchange, they have a canted strcuture with the ferromagnetic component parallel to the (j) sublattice magnetization.     

Dilute 57Fe and 151Eu as Probes for Magnetism in Ruthenium Magneto-Superconductors

Hyperfine Interactions - Mössbauer studies of 151Eu and/or dilute 57Fe in ruthenium oxides; R2?x Ce x Sr2RuCu2O10 (R=Eu, Gd), SrRuO3, CaRuO3, EuSr2RuCu2O8, EuSr2RuO6, Eu2RuO5 and...     

The study of Mössbauer effect in EuBa2Cu3O7-y

EuBa₂(Cu_1-xFe_x)₃O_7-x has been investigated by the⁵⁷Fe and¹⁵¹Eu Mössbauer effect. The⁵⁷Fe Mössbauer spectra of the EuBa₂(Cu_1xFe_x)₃O_7-y without or with DC electric current (the current strength I=0.5A) around the superconducting transition temperature have been measured. The results indicate that the isomer shift (IS) and the quadrupole splitting (QS) of the Fe replacing the Cu(2) vary neither with increasing the Fe content nor with the small DC eletric, current passing the superconductor and that the IS and the QS of the Fe replacing the Cu(1) vary with the Fe content. Especially, the IS and the QS of the Fe (D3) replacing the Cu(1) are changed when the small electric current passes the superconductor at 80K.     

155Gd Mössbauer investigation of the magnetic order and spin-reorientation in Gd3Ag4Sn4

In a recent study of the magnetic order in Gd₃Ag₄Sn₄ by neutron powder diffraction and ¹¹⁹Sn Mössbauer Spectroscopy we showed that both the Gd(2d) and Gd(4e) sublattices order antiferromagnetically at 28.8(2) K. We also demonstrated that the ‘magnetic event’ around 8 K is in fact a ‘plane to axis’ spin-reorientation of the Gd magnetic structure. Here, we extend our study with ¹⁵⁵Gd Mössbauer Spectroscopy. The initial magnetic ordering at 30(2) K is clear for both sites and substantial changes in the hyperfine fields are observed at 8 K when the magnetic structure reorients.     

Magnetic ordering in rare earth iron silicides and germanides of the RFe2X2 type

Rare earth iron silicides and germanides of the RFe₂Si₂ or RFe₂Ge₂ type with R = La, Ce, Pr, Nd, Sm, Gd and Dy were measured for their magnetic susceptibility. The silicides and germanides of Nd and Gd are antiferromagnetically ordered below a Neel point of, respectively, 11 and 7°K for the silicides and 13 and 11 for the germanides. The Nd sublattice under-goes a spin-flop transition which at 4.2°K is at 11 KOe. Although the Fe sublattice is diamagnetic, all the samples showed a weak ferromagnetic ordering below a temperature of about 700°K. The ratio between the dia- and ferromagnetic phases is 94:6 per cent in the silicides and 80:20 in the germanides, as determined by Mössbauer spectroscopy and supported by magnetization measurements.     

Hyperfine interactions on151Eu and57Fe in amorphous EuFe2Si2

The magnetic and quadrupole hyperfine interactions in amorphous EuFe₂Si₂ have been measured using⁵⁷Fe and¹⁵¹Eu Mössbauer spectroscopy. The distributions in the various parameters have been found using the Fourier coefficient method. Novel features of the results are that the Eu charge state (4f occupation number) changes between the crystalline and amorphous phases and that whereas in the crystalline phase neither Eu nor Fe is magnetic, both become so in the amorphous phase.