Mössbauer measurements in CuFeTe2

The Mössbauer measurements at variable temperature (from liquid helium to room temperature) on the layered compound CuFeTe₂ have been able to determine the existence of a magnetically ordered state below T _N= 254 ± 15 K. The general shape of the spectra and the magnitudes of the hyperfine fields let us to propose a Spin Density Wave (SDW) behavior for this compound.     

Superconducting and magnetic properties of the oxide superconductors La1.85Sr0.15Cu1−xFexO4

Mössbauer and magnetic measurements have been made in the perovskite superconductors La_1.85Sr_0.15Cu_1−x ⁵⁷Fe_xO₄ for x=0.0025, 0.005, 0.01, 0.05 and 0.10. The superconducting transition temperature is rapidly depressed as x increases, reaching T_c=0 for x≈0.03. Mössbauer data for x=0.05 show behavior below ≈15 K which indicates magnetic ordering. Magnetic susceptibility data give an effective moment of 3–4 μ_B/Fe atom, and a hand-like susceptibility which increases with x.     

Mössbauer study of 1/8 anomaly in La2−x Ba x CuO4

The measurements of Mössbauer effect, magnetic susceptibility and muon spin relaxation have been carried out for the high-T _c superconductor La_2?x Ba _x CuO₄. The intensity of Mössbauer doublet spectrum of the sample of x～1/8 begins to decrease rapidly at a certain temperature T _m, which we define as a magnetic transition temperature T _Möss. This temperature almost agrees with T _μSR determined from muon spin relaxation. The quadrupole doublet disappears at low temperature below T _m but a clearly splitted spectrum is not observed even at 4.2 K, which indicates a peculiar magnetic state with a wide distribution of internal magnetic field. Around x～1/8, the superconducting critical temperature T _c and T _m are competed each other. In conclusion, superconductivity disappears around 1/8 hole concentration and a peculiar magnetic state such as spin density wave appears.     

The magnetic transition in Fe-substituted hexagonal β-Al9SiMn3 phase

Recently we have studies β-Al₉Si(Mn_1?x Fe _x )₃ using Mössbauer effect spectroscopy withx=0.28 and discovered a new transition at about 80 K. Neutron diffraction studies down to low temperatures reveal no structural changes, so that this transition at 80 K is indeed of magnetic origin. The magnetic susceptibility shows a small maximum near this temperature superimposed on a large Curie-like background. In addition to this transition, the Curie-like background shows a cusp near 4 K. We thus infer a magnetic double transition in this disordered alloy. These magnetic transitions have been followed to lower Fe concentrations (x=0.10 and 0.20) by both Mössbauer spectroscopy (T _c ) and by magnetic susceptibility (T _g). It is found thatT _C decreases rapidly with decreasing Fe concentration, whileT _g remains relatively constant. The saturation hyperfine fieldB _hf(0) decreases rapidly with decreasingx, indicating that the Fe atoms loose their magnetic moments in the limit of infinite dilution, and the important role played by Fe?Fe nearest neighbors in determining the magnetic properties.     

151Eu Mössbauer spectroscopic, electric, and magnetic measurements of EuAgGe and EuAuGe

The physical properties of EuAgGe and EuAuGe, the structures of which are derived from the CeCu₂ type, have been investigated in detail by means of magnetic susceptibility, electrical conductivity and ¹⁵¹Eu Mössbauer measurements. Above 50 K both germanides show Curie--Weiss behavior with experimental magnetic moments of \mu _exp=7.70(5) \mu _B (EuAgGe) and \mu _exp=7.40(5) \mu _B (EuAuGe) and Weiss constants of -2(1) K (EuAgGe) and 33(1) K (EuAuGe). For EuAgGe, a magnetic phase transition is observed below 18(1) K. Zero-field cooling and field cooling measurements indicate cluster glass behavior (weak ferromagnetism, mictomagnetism). Magnetization measurements at 5 K show a saturation magnetic moment of 3.3(2) \mu _B/Eu at 5.5 T. ¹⁵¹Eu Mössbauer measurements show a Eu(II) valence state (\delta =-10.4 mm/s). While magnetic hyperfine splitting appears in the spectra at temperatures as high as 15 K, complete magnetic ordering is not reached at temperatures down to 4.2 K. EuAuGe orders ferromagnetically at 32.9(2) K. Magnetization measurements at 2 K show a saturation magnetic moment of 6.2(1) \mu _B/Eu at 5.5 T, respectively, indicating that all spins are ordered ferromagnetically at low temperatures. ¹⁵¹Eu Mössbauer measurements show a Eu(II) valence state (\delta =-10.6 mm/s) and two spectral components in an approximate 1:1 ratio, subjected to magnetic hyperfine splitting effects at T₁=32(2) and T₂=18(4) K, respectively. Thus, the transition temperature of 32.9 K observed in the susceptibility measurements appears to be associated with ordering of only one of the two crystallographically distinct europium sites in this compound. Electrical conductivity measurements indicate metallic behavior for both germanides.     

Etude d'un nouveau type de fluorure antiferromagnetique a caractere bidimensionnel: NaFeF4

A new type of two-dimensional antiferromagnetic structure has been investigated by magnetic susceptibility measurements, neutron diffraction and Mössbauer resonance. The magnetic cell of NaFeF₄ is doubled along the a axis and the spins lie along the b axis. The κ^-1 vs T curve shows a sharp minimum at about 105 K close to the three-dimensional transition temperature determined by Mössbauer spectrometry (111.5 K). A calculation of z. snfc;J/kz. snfc; has been performed using a high temperature series expansions technique (J/k = -23 K). The variation of the hyperfine field in the range 0.6 ?T/T_N? 1 gave the value of the critical exponant β = 0.25.     

Intermediate electronic relaxation betweenS=3/2 andS=1/2 states in Fe(J-mph)NO with a jäger-type ligand J-mph

The incomplete spin transition between the low-spin (LS) (S=1/2) and the intermediate-spin (IS) (S=3/2) states in the iron (III) complex Fe(J-mph)NO (mph=4-methyl-o-phenylene), centered atT _c≈212 K, has been studied with⁵⁷Fe Mössbauer spectroscopy and magnetic susceptibility measurements between 80 K and 320 K. The lineshape of the Mössbauer spectra is well reproduced by a two state stochastic relaxation model resulting in values of about 2·10⁶ s^?1 to 7·10⁶ s^?1 for the IS→LS transition rate constantk _IL. The kinetics of this spin transition can be described by an Arrhenius equation yielding activation energiesE _IL=1.1 (2) kJ/mol andE _LI=6.1 (2) kJ/mol for the IS→LS and LS→IS conversion, respectively.     

Magnetic properties and spin order of Sr7Fe10O22

The magnetic properties of Sr₇Fe₁₀O₂₂ have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature T_N = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to T_N.The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.     

Mössbauer study of Fe‐doped CuGeO3 system Cu0.9Ge0.9Fe0.2O3

The Fe‐doped system Cu_0.9Ge_0.9Fe_0.2O₃ has been investigated by means of X‐ray diffractometry, Mössbauer spectroscopy and superconducting quantum interference device. The structure of this system is orthorhombic and the lattice constants are a=4.784 Å, b=8.472 Å and c=2.904 Å, respectively. Magnetic measurements confirm that the spin‐Peierls transition appears in our sample at about 12 K, which is near to the spin‐Peierls transition temperature (T _sp) 14 K of pure CuGeO₃ system. The Mössbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe³⁺ ions from room temperature to 4.2 K. The Mössbauer parameters show a discontinuity near T _sp. The jump of the magnetic hyperfine field at temperatures lower than T _sp means increasing of the superexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrement in symmetry of lattice sites and spontaneous thermal contraction.     

Magnetic and Mössbauer characterization of the magnetic properties of single-crystalline sub-micron sized Bi2Fe4O9 cubes

Magnetic and Mössbauer characterization of single crystalline, sub-micron sized Bi₂Fe₄O₉ cubes has been performed using SQUID magnetometry and transmission Mössbauer spectroscopy in the temperature range of 4.2 K ≤ T ≤ 300 K. A broad magnetic phase transition from the paramagnetic to the anti-ferromagnetic state is observed below 250 K, with the Mössbauer spectra exhibiting a superposition of magnetic, collapsed and quadrupolar spectra in the transition region of 200 K < T < 245 K. Room temperature Mössbauer spectra obtained in transmission geometry are identical to those recorded in back-scattering geometry via conversion electron Mössbauer spectroscopy, indicating the absence of strain at the surface. A small hysteresis loop is observed in SQUID measurements at 5 K, attributable to the presence of weak-ferromagnetism arising from the canting of Fe³⁺ ion sublattices in the antiferromagnetic matrix.     

Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.     

CEMS spectra of non-spherical nanoparticles in oxidized iron thin films

The polycrystalline stannide SmRhSn was prepared by arc melting of the elements in an argon atmosphere. The title compound crystallizes with the ZrNiAl type structure (space group $P\bar{6}2m)$ with the lattice parameters: a?= 739.6(1) and c?= 406.9(1) pm. The magnetic and electronic properties of SmRhSn were investigated in detail by magnetic susceptibility measurements and ¹¹⁹Sn Mössbauer spectroscopy. A transition from a paramagnetic to a ferromagnetic state was determined to be T _C?= 14.5(1) K. The ¹¹⁹Sn Mössbauer spectrum recorded in T?= 4.2 K was fitted using single component, but with a broad quasi-distribution of magnetic hyperfine fields.     

151Eu Mössbauer Spectroscopy in La0.38Eu0.29Ca0.33MnO3

Electrical conductivity with and without magnetic field, d.c. magnetization and ¹⁵¹Eu Mössbauer studies were carried out in La_0.38Eu_0.29Ca_0.33MnO₃ perovskite manganite system. An insulating ground state is found throughout the temperature range with charge ordered (CO) state emerging at T _CO ～ 140 K, where as an external magnetic field of 6 T induces metal-insulator transition at ～120 K. D.C. magnetization measurements show the antiferromagnetic (AFM) transition occurring at T _N ≈ 48 K. The temperature dependent ¹⁵¹Eu Mössbauer measurements showed that the substituted Eu replaces La³⁺ in the 3+ charge state and a small magnetic moment gets induced at the Eu nucleus at low temperatures. The anomalous variation of the f- factor with temperature occurring around T _N and T _CO corroborates the occurrence of antiferromagnetic (AFM) and charge ordering (CO) transition, respectively.     

Hyperfine fields on59Co in ReCo2

We report⁵⁷Fe Mössbauer measurements in the diluted antiferromagnetic (AF) Fe_xZn_1?xF₂ withx=0.25 at temperatures between 4.2 and 28 K. DC susceptibility measurements show a spin-glass (SG) phase at low temperatures forx?0.3. Our Mössbauer spectra show a competitive coexistence of an SG phase and AF order. We propose an interpretation in terms of clusters in the AF order and some spins exhibiting SG behavior.     

Mössbauer effect on YFe3 compound

The thermal variation of the Mössbauer parameters of the YFe₃ compound between 78 K and T_c is studied. The results agrees well with the magnetic measurements. For the iron site 18 (h) the presence of an anisotropic interaction splits the Mössbauer spectrum into two six-lines patterns with the intensities in 2:1 ratio but above 400 K the intensities of the Mössbauer spectra of the sublattices are in 1 : 2: 6 ratio in agreement with crystallographic data.     

Magnetic ordering in57Fe-doped high-T c superconductors

The high-temperature superconductor, Tl₂CaBa₂(Cu_1?x Fe _x )₂O_8+δ (the 2122 compound), has been investigated by a number of techniques, including X-ray diffraction, resistance and ac susceptibility measurements, and Mössbauer spectroscopy. The procedures followed to make close to single-phase samples are described. The decrease in the critical temperature for superconductivity,T _c , is less than for the iron-doped 123 compounds. The Mössbauer spectra at 77 K and above consist of an asymmetric doublet. Below about 10 K magnetic hyperfine splitting occurs; relaxation effects are still present at 2.3 K. The spectra can be fitted with two overlapping patterns. Their origin is discussed: comparisons are made with other high-T _c superconductors.     

Spin conversion detected by Mössbauer spectroscopy and μSR on a 1D FeII paramagnetic chain

While magnetic properties of the 1D chain [Fe(hyetrz)₃](4-bromophenylsulfonate)₂ investigated over the temperature range from 300 K to 2 K show paramagnetic behavior, detailed ⁵⁷Fe Mössbauer and muon spin relaxation measurements reveal an unexpected spin conversion. Approximately ~14 % of the high-spin ions are found to convert to the low-spin state with a transition temperature T _1/2?~?120 K.     

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 properties of the pseudo-binary Fe2(Nb1-xMnx)

The magnetic behavior of the pseudo-binary system Fe₂(Nb_1-xMn_x) is investigated by means of the experimental techniques of X-ray diffraction (XRD), Mössbauer Spectroscopy (MS) and magnetization studies. The XRD results indicate that, up to x=0.3, all samples are single phase with hcp structure. This corresponds to the solubility limit of manganese in this phase. Above x=0.3, all prepared samples present the coexistence of three phases, two with hcp structure and one fcc. The magnetization measurements at low temperatures indicate that the transition temperature increases with the addition of Mn atoms in the Fe₂Nb host (T_N=10 K) up to 58 K for x=0.1. The Mössbauer spectra were fitted with a quadrupole splitting distribution, which indicates that the average quadrupolar splitting increases slightly with the increase of the manganese concentration.     

Mössbauer and magnetic characterization of TbRhSn

The intermetallic compound TbRhSn was investigated in detail by X-ray, magnetic susceptibility measurements and ¹¹⁹Sn Mössbauer spectroscopy. This compound undergoes a transition from a paramagnetic to an antiferromagnetic state at T _N = 20.8(2) K. The ¹¹⁹Sn Mössbauer spectrum recorded at 4.2 K can be well fitted as a composition of three subspectra with the same intensities, magnitudes of H _hf, ΔE _Q, and δ _is, in agreement with the model of triangular-like antiferromagnetic arrangements of equal magnetic Tb moments lying in the basal ab-plane deduced from neutron diffraction studies (Szytu?a et al., J Alloys Compd 244:94–98, 1996).