Effects of nitrogen and vanadium on the57Fe hyperfine field of RFe12−x V x N y (R=Y,Nd)

Magnetization and⁵⁷Fe Mössbauer measurements were carried out on RFe_12–x V _x N _y compounds (R=Y and Nd,x=1.7 and 2.2) and the effects of nitrogen and vanadium atoms on the⁵⁷Fe hyperfine fields at the different iron crystallographic sites were investigated. The hyperfine field decreases with increasing number of vanadium neighbour atoms at all the iron sites. The hyperfine field is strongly enhanced in the nitrogen composition withy>1 where the compound tends to transform into an amorphous-like solid. The iron moment deduced from the hyperfine field increases more upon nitrogenation for the 8i-site than for the other sites, and exceeds the moment of bcc iron.     

Iron-57 Mössbauer spectroscopy study of phases in the CaZrTi2−2x Nb x Fe x O7 zirconolite system

Materials of composition CaZrTi_2?2x Nb _x Fe _x O₇ with the fluorite-related zirconolite structure have been prepared. The ⁵⁷Fe Mössbauer spectra show that iron is initially located in the five co-ordinate cation sites. As the iron content increases the iron enters the octahedral sites until, at a composition CaZrTi_0.4Nb_0.8Fe_0.8O₇, ca. 50% of the iron is five co-ordinate and the remainder is located in the octahedral sites.     

Phase transformations in perovskites TbBaCo2−x FexO5 + γ

The transport, magnetic, and elastic properties of TbBaCo_2?x Fe_xO_{5 + γ} are investigated. It is shown that these compounds exhibit first-order metal-insulator and antiferromagnet-weak ferromagnet transitions in the orthorhombic phase (x < 0.12), while these transitions are not observed in the tetragonal phase (x > 0.12). In the concentration range corresponding to the orthorhombic phase, doping with iron stabilizes the weakly ferromagnetic phase. However, the tetragonal phase is antiferromagnetic. Oxygen vacancies are assumed to be ordered in the orthorhombic case and disordered in the tetragonal phase. An analysis of Young’s modulus, magnetostriction, and effects of pressure and substitution of the O¹⁸ oxygen isotopes for O¹⁶ indicates a weak correlation between magnetic transformations and the crystal lattice.     

A Mössbauer study of octahedral site symmetries in systems Co x Mn3−x−y Fe y O4 and Ni x Mn3−x−y Fe y O4

A Mössbauer study of cation distribution in systems Co _x Mn_3?x?y Fe _y O₄ and Ni _x Mn_3?x?y Fe _y O₄ has been made. It has been found that in both systems all specimens withy<0.6 value exhibit quadrupole doublets corresponding to site symmetries Fe³⁺(I) and Fe³⁺(II) of octahedral site. As more and more cobalt or nickel is introduced into the matrix the intensity of the inner quadrupole doublet increases while on introducing iron that of the outer quadrupole doublet increases. After a certain concentration of iron the inner doublet starts becoming more intense. It is suggested that this arises possibly from the substitution of cations in the second co-ordination sphere of Fe³⁺(I) and Fe³⁺(II) sites. Fory>0.6 the Mössbauer spectra show relaxation effects.     

Magnetic studies of Bi x Y3-x Fe5O12 fabricated using conventional method

A series of Bi substituted yttrium iron garnet (Bi-YIG) nanoparticles with nominal formula of Bi _x Y_3???x Fe₅O₁₂ in which x varied in steps of 0.0, 0.25 and 0.5 are prepared by conventional method. Vibration sample magnetometer (VSM) at Room temperature (RT) shows saturation magnetization decreases from 27.4 to 25.2 (emu/g) as x value increases from 0.0 to 0.5. Room temperature ⁵⁷Fe Mössbauer spectra are recorded for these series. The hyperfine field value for octahedral and tetrahedral of samples increases from 484 and 390 kOe to 491 and 397 kOe respectability, as Bi replaces Y in (Bi _x Y_3???x Fe₅O₁₂) atom with increasing x value. The effect of Bi^3?+? substitution for Y^3?+? on lattice constants, morphology and magnetic properties of pure YIG has been investigated.     

119Sn Mössbauer spectroscopy of U x Th1−x CoSn and UCoAl1−x Sn x

Magnetization and¹¹⁹Sn Mössbauer spectroscopy studies were performed on two pseudoternary systems, namely U _x Th_1?x CoSn and UCoAl_1?x Sn _x . Magnetic hyperfine fields on¹¹⁹Sn nuclei were found to be due to local surrounding of U atoms which carry magnetic moments. In pure UCoSn the valuesB _hf=8.66 T and μ_∪ satisfy the relationB _hf=6.75 μ_B found for a number of UTX compounds studied. Local surrounding effects are indicated by multicomponent spectra obtained for the two pseudoternary series.     

Magneto-crystalline properties of BaFe12−2x M x Sn x O19 (M = Sn, Ni, Zn) ferrite powders

BaFe_12?2x M _x Sn _x O₁₉ compounds, where M?=?Sn²⁺, Ni²⁺ or Zn²⁺ ions, were synthesized by mechanical milling and partially by citrate precursor methods. Analysis of magneto-crystalline structure has been carried out by Mössbauer spectroscopy. The Sn⁴⁺ ions replace Fe³⁺ ions on 2b and slightly on 2a?+?4f₁ sites, Zn²⁺ ions strongly prefer 4f₁ sites, Sn²⁺ ions prefer 4f₁ sites too and Ni²⁺ ions occupy 4f₂ and 12k or 2a sites. The magnetic properties were evaluated by the vibrating sample magnetometry and the thermomagnetic analysis. A large variation of the intrinsic coercivity H _c (330 to 78 kA/m) and of temperature coefficient of coercivity of ΔH _c /Δ? (0.39 to 0.22 kA/m°C) were achieved as a function of the (Zn–Sn) and (Sn–Sn) substitutions, respectively. The Curie temperature T _c decreased with the (Ni–Sn) substitution from 447 to 399°C.     

Increase in the magnetostrictive susceptibility of Tb0.3Dy0.67Ho0.03Fe2−x Co x alloys upon substitution of cobalt for iron

This paper reports on the results of investigations into the concentration dependences of the magnetostrictive susceptibility, the magnetostriction, the magnetization, and the Curie temperature for Tb_0.3Dy_0.67Ho_0.03Fe_2?x Co _x alloys upon substitution of cobalt for iron. It is revealed that the temperature of the spin-reorientation transition shifts toward room temperature with an increase in the cobalt content in the range 0 ≤ x ≤ 1.3. Substitution of cobalt for iron in the alloys leads to a decrease in the contribution of the 3d transition metal sublattice to the magnetic anisotropy owing to the opposite signs of the single-ion anisotropy constants for iron and cobalt. The decrease observed in the magnetocrystalline anisotropy compensated in both rare-earth and 3d transition metal sublattices is responsible for the high magnetostrictive susceptibility of the studied compounds at a high cobalt content (x = 1.3) in the room-temperature range.     

Magnetic and Mössbauer effect study of laves phases of U x Fe100−x (x=32, 33.3 and 35)

⁵⁷Fe Mössbauer effect measurements have been made on U _x Fe_100?x (x=32, 33.3, and 35) samples at 300 and 78 K. Laves phase structure was maintained for all three samples. Mössbauer spectra of the three samples were found to be a symmetric quadrupole doublet at 300 K. Such spectra were converted into a set of two overlapping six lines pattern at 78 K. The values of the hyperfine fields have been found to vary systematically with the iron content in the samples. The Curie temperatures, as determined by the ac susceptibility measurements, have been found to increase by increasing the amount of iron in the samples.     

Two-dimensional spin freezing in Y1−z Ca z Ba2Cu3−x Fe x O7

Hyperfine electric and magnetic interactions in Y_1?z Ca _z Ba₂Cu_3?x Fe _x O_6+y compounds have been studied for different rates of Fe and Ca substitution (x=0.09 and 0.24;z=0.24;y=0?1) by⁵⁷Fe Mössbauer spectroscopy of powder samples obtained by different thermal treatments. Calculations of the Fe³⁺ EFG tensor have been performed for different coordination polyhedra in Cu1 and Cu2 sites. Variations of the direction, amplitude and of the sign of the principal component of the EFG are reported versus the iron displacement from the ideal Cu sites inside the pyramidal and tetrahedral coordination polyhedra. Calculated ΔE _Q and η values are compared with the experimental ones. For the Cu2 site, faithfully probed in both oxygen-depleted and oxygen-saturated samples by fairly large fraction of residing iron atoms, the mutual orientations of the axes of the principal EFG component and that of easiest magnetization are deduced from interrelations between quadrupole parameters for paramagnetic quadrupolar and magnetic Zeeman Mössbauer spectra. In the desoxygenated samples, the coexistence of a long range 2D antiferromagnetic order and of a spin-glass order has been evidenced. For the oxygen-saturated samples, the two-dimensional spin-glass order is observed belowT _f =10 K. The Mössbauer spectra under applied fields at 4.2 K show an easy polarization of the spins in the Cu2 sites.     

Features of local crystallographic, magnetic, and valence states of iron ions in Bi1 − x Sr x FeO3 perovskites at x = 0–0.67

Perovskites of the Bi_{1 ? x} Sr _x FeO₃ system (x = 0–0.67) at T = 295 K and T > T _N are studied using the Mössbauer effect. When the strontium content x = 0.1–0.15, the structural transition from the rhombohedral to the cubic phase takes place. It is found that in samples of the Bi_{1 ? x} Sr _x FeO₃ system (x = 0.07–0.67), there are only two structurally nonequivalent states of iron ions that correspond to Fe³⁺ ions in octahedral and tetrahedral oxygen environments.     

Mössbauer and X-ray investigations of YBa2−x Sn x Cu3O7−δ superconductors

Mössbauer spectra of YBa_2?x Sn _x Cu₃O_7?δ compounds withx=0.2 and 0.3 have revealed two components, both with isomer shifts corresponding to 4⁺ valency for Sn. The temperature dependence of the area of only one component shows an anomaly near the superconducting temperature for both samples, thus suggesting anisotropic behaviour for the lattice rigidity. In the case ofx=0.2 sample X-ray diffraction studies further indicate similar anomaly in the orthorhombic strain. It is concluded that such anomalies are precursors for the superconductivity to occur in these compounds.     

Hyperfine interactions of181Ta in Ni1−x Hf x

Time-differential angular correlation technique was employed for studies of the system Ni_1?x Hf _x . The hyperfine interactions of¹⁸¹Ta especially in the intermetallic compounds Ni₅Hf, Ni₇Hf₂, NiHf, NiHf₂ and in solid solutions of Hf in Ni have been investigated.     

Mössbauer study of spinel system ZnMn1−x Cr x FeO4

Mössbauer effect of the system of spinels ZnMn_1?x Cr _x FeO₄ is studied forx having values 0, 0·2, 0·4, 0·5, 0·6, 0·8 and 1·0. These compounds show quadrupole splitting which increases with increasing Mn³⁺ ion concentration. It abruptly increases at Mn³⁺ ion concentration at which crystal structure also changes.     

Accurate determination of the Mössbauer spectrum hyperfine parameters and correlation withT c in YBa2Cu3−x 57Fe x O7−δ (0.01≦x≦0.15)

High statistics room temperature Mössbauer spectra have been performed on ten YBa₂Cu_3?x Fe _x O_7?δ (0.01≦x≦0.15) samples. The different fit solutions (including broadening of the lines) are tested with “χ²” factor analysis. Only two solutions are valid with almost similar parameters. The results on present samples and our previous results on various materials made under different heat treatments show thatT _c is governed byx and the relative population of one of the iron species. These species can be related to highly coordinated irons in the chains.     

Local states of iron ions in multiferroics Bi1−x La x FeO3

Mössbauer studies of perovskites Bi_1?x La _x FeO₃ (x = 0, 0.10, 0.20, 0.61, 0.90, 1.00) were conducted at 295 and 87 K. The spatial spin-modulated structure (SSMS) observed in perovskites BiFeO₃ and Bi_0.9La_0.1FeO₃ leads to a specific distribution of hyperfine fields P(B) with two peaks. Substitution of La for Bi (x = 0.2) destructs the SSMS. The concentration dependences of the hyperfine field (B), isomer shift (?) and quadrupole shift (δ) were measured. The iron ions are in the trivalent state. The local magnetic moments μ(Fe) of the Fe³⁺ ions are determined.     

Measurement of the cation partitionings in FexV3−xS4 (x = 1.0 and 2.0) by powder neutron diffraction

Full profile analyses of powder neutron diffraction data have provided direct measures of the cation partitionings in the ternary sulfides Fe_xV_3−xS₄, x = 1.0 and 2.0. In Fe₂VS₄, the cation sites of type I in the metal-deficient layers are completely populated by iron atoms, giving a structural formula Fe^IFe^IIV^IIS₄. In FeV₂S₄, in contrast to earlier results, the partitioning of the iron atoms is found to be incomplete, the corresponding structural formula being Fe_0.72^IV_0.28^IFe_0.25^IIV_1.75^IIS₄. In both materials, the diffraction data suggest that the distributions of iron and vanadium atoms in the metal-rich layers are non-random. The present structural results are considered in relation to those from earlier experiments on this system.     

Mössbauer studies of ɛ-Fe3−x Ni x N and γ′-Fe4−y Ni y N nanoparticles

Nanocrystalline ?-Fe_3?x Ni _x N (0.0?≤?×?≤?0.8) particles are synthesized by precursor technique and nitridation of decomposed products in NH₃ (g) in the temperature range 673 K-823 K. For x?=?0.1–0.4 compositions, single phase ?-Fe_3?x Ni _x N hexagonal structure with space group P6₃/mmc is formed, while for x?=?0.5–0.8, fcc γ′-Fe_4?y Ni _y N phase is also precipitated. The room temperature Mössbauer spectrum for all the compositions shows the presence of superparamagnetic doublet, which is attributed to ?-Fe_3?x Ni _x N phase. For x?=?0.5–0.8 compositions, two additional sextets are observed corresponding to two different iron sites, the corner position (Fe^c) and the fcc position (Fe^f), in γ′-Fe_4?y Ni _y N. The added Ni atoms preferentially substitute the corner Fe^c positions. The isomer shift, quadrupole splitting and hyperfine field values are found to change with the Ni content.     

A survey on the effect of vanadium content on the magnetoelastic properties of YFe12−xVx alloys

Experimental results on the thermal expansion and magnetostriction of YFe_12−xV_x (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5 T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5 T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe_12−xV_x compounds.     

Hyperfine interactions in Zr(Fe1−x Al x )2 measured forx≤0.20 by TDPAC and Mössbauer spectroscopy

Mössbauer (⁵⁷Fe) and TDPAC spectroscopy (¹⁸¹Hf) have been used to study quasibinary compounds Zr(Fe_1?x Al _x )₂ forx≤0.20. It has been found that the dependence of the mean values of the hyperfine magnetic field, quadrupole splitting and isomer shift on the Al concentrationx is strong. The dependence of the hyperfine magnetic field on the number of Al atoms as nearest and next-nearest neighbours of⁵⁷Fe has been established. The TDPAC results also indicate a dependence of the hyperfine field on¹⁸¹Ta on Al concentration.