La solution solide Cr1−xRhxO2

A new solid solution Cr_1?x,Rh_xO₂ (0?x?1) has been prepared using oxidizing acids or ammonium perchlorate under pressure. The magnetic study suggests that chromium (IV) and rhodium (IV) are present in the structure at x ? 0.2 and chromium (V) and rhodium (III) at 0.2 < x ? 0.5. Forx > 0.5 increasing rhodium (IV) content gives rise to properties similar to those of RhO₂.     

Phase diagram and oxygen annealing effect of FeTe1−xSex iron-based superconductor

Phase diagrams of as-grown and O₂-annealed FeTe_1?xSe_x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x≥0.15, and weak superconductivity appeared when x≥0.1. Beginning at x=0.5, weak superconductivity was found to evolve into bulk superconductivity. Interestingly, for O₂-annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x≥0.1. We found that O₂-annealing induces bulk superconductivity for FeTe_1?xSe_x. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk superconductivity.     

Systematic Mössbauer study of YBa2Cu3−x Fe x Oδ and PrBa2Cu3−x Fe x Oδ as a function of temperature

We study the similitudes and differences between YBa₂Cu_3?x Fe _x O_δ and PrBa₂Cu_3?x Fe _x O_δ systems, using Mössbauer spectroscopy. Both systems, withz=0.04, were studied at several temperatures. The spectra of PrBa₂Cu_3?x Fe _x O_δ showed four asymmetric quadrupole doublets with apparently different line widths, which were fitted with four symmetric superimposed quadrupole doublets with the same line width, but assuming a small (～4–6 kOe) residual magnetic field in the Fe sites, which are mainly the Cu(1) sites of the 1–2–3 structure. On the other hand, the PrBa₂Cu_3?x Fe _x O_δ spectra showed only three asymmetric quadrupole doublets which can be fitted with three superimposed symmetric doublets and a residual magnetic field. In this case, the Fe atoms also occupy the Cu(1) sites of the 1–2–3 structure. The temperature variations of the Mössbauer spectra and their parameters seem to indicate that, in the Pr-system, a structural change takes place between 12 K and 40 K.     

The origin of magnetism in UNi2 — a simple band approach

The magnetization and susceptibility investigation of pseudo-binary U(Ni_1?xFe_x)₂ and U(Ni_1?xCu_x)₂ for chosen concentrations of x ? 0.1, x ? 0.8, and x ? 0.06, respectively, are presented. The most significant result is that the substitution of Ni (in UNi₂) by Fe reduces both the magnetic moment and the ordering temperature rapidly although it appears to be established that the magnetic moment of UFe₂ is predominantly residing on the Fe sites. The small concentration of Cu substituted into UNi₂, on the other hand, increases the magnetic moment. The obtained results are discussed together with those of U(Ni_1?xCo_x)₂ and seem to support the recently proposed explanation on the origin of magnetism in UNi₂.     

Influence of magnetic ordering on the structural properties of dilute copper ferrites

The x-ray structural properties of samples in the CuGa_xAl_xFe_2?2x O₄ (x = 0?0.7) and CuGa_xAl_2x Fe_2?3x O₄ (x = 0?0.5) systems are studied. It is found that magnetic ordering in dilute copper ferrites affects their structural properties. It is concluded that the frustration of magnetic coupling leads to suppression of the cooperative Jahn-Teller effect in dilute copper ferrites with a frustrated magnetic structure.     

Investigations on magnetically-dilute CoxZn1−x Rh2O4 spinel solid solution

Magnetic measurements have been performed on polycrystalline solid solutions Co_xZn_1?xRh₂O₄ with a spinel structure. The samples with 0.50? x ? 1.00 are antiferromagnets. The samples with x?0.40 do not show a magnetic order, and their magnetic behavior can be explained taking into account the presence of finite clusters of Co²⁺ ions and paramagnetic isolated ions.     

Setup for studying nonlinear magnetic properties of high-temperature superconductors with the aid of magnetization harmonics

A setup for measuring cophasal and quadrature components of higher harmonics of an electromotive-force signal of the response of a high-temperature superconductor makes it possible to study nonlinear magnetic properties of superconductors in variable magnetic fields of up to 1 kOe and constant magnetic fields of up to 10 T in the temperature range of 5?C300 K. This setup was used to measure the temperature dependences of the absolute values of the real and imaginary parts of the first and third harmonics of the magnetization of textured Yba₂Cu₃O_{7 ? x} polycrystalline samples in the temperature range of 77?C220 K at various values of variable and constant magnetic fields. An analysis of resulting data made it possible to reveal the presence of different dynamical modes of the magnetic flux in YBa₂Cu₃O_{7 ? x} that were dominant in different temperature ranges. The nonlinearity of the magnetization of YBa₂Cu₃O_{7 ? x} (the appearance of higher harmonics) was observed up to temperatures in the range of T = 103?C112 K, which were substantially higher than the temperature of the transition of this compound to a superconducting state. The observed feature in the magnetization of YBa₂Cu₃O_{7 ? x} was associated with the emergence of a pseudogap state in this compound.     

Crystal structure and photoluminescence of (Ba1−x−ySryEux)9Sc2Si6O24

Divalent europium-doped alkaline earth metal silicate phosphors, (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (x=0.005–0.1, y=0–0.95), have been successfully prepared by solid-state reaction at 1350 °C. The analysis of X-ray diffraction shows that the compounds are in a single phase at the proper concentration of Sr²⁺. At room temperature, the Eu²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor exhibits a single emission band peaking at about 506 nm. With the increasing content of Sr²⁺, the luminescent intensity of (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ weakens, and the emission peak shifts towards red. Luminescence concentration quenching occurs when Eu²⁺ content x is more than 1 mol% in (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (y=0/0.2). At low temperatures (Ba_0.9?ySr_yEu_0.1)₉Sc₂Si₆O₂₄ (y=0/0.2) phosphors have two emission bands corresponding to different Eu²⁺ crystallographic sites. The high energy peak (P₁) is quenched at room temperature, while the low energy peak (P₂) weakens much more slowly owing to the energy transfer from P₁ to P₂.     

Synthesis and magnetic properties of Mn–Zn ferrite nanoparticles

Mn–Zn ferrite nanoparticles (Mn_1−xZn_xFe₂O₄) are synthesized by a hydrothermal precipitation approach using metal sulfate solution and aqueous ammonia. The analysis methods of XRPD, TEM, TGA, and VSM are used to characterize the magnetic nanoparticles. Through the characterization of the precipitated nanoparticles, the effects of the reacting component proportions and preparation techniques on the Curie temperature, the magnetization, and the size distribution of Mn–Zn ferrite nanoparticles are discussed. Furthermore, the Mn–Zn ferrite nanoparticles are used to prepare ferrofluid. Variation of the magnetic properties of the ferrite nanoparticles with the composition content x of Zn and the magnetic moment of the nanoparticles are discussed.     

Study of structural and ferromagnetic properties of pure and Cd doped copper ferrite

This report presents the synthesis of copper cadmium ferrite (Cu_1−xCd_xFe₂O₄, x=0.3, 0.4, 0.5, 0.6 and 0.7) by the citrate precursor method and its subsequent characterization by X-ray diffraction (XRD), differential scanning calorimetry, infrared spectroscopy and ferromagnetic resonance. XRD results confirm the single cubic spinel phase formation with the particle size of 40 nm, which decreased up to 20 nm with increase in Cd content, while the lattice parameter increased with increase in Cd content. A significant change in the magnetic properties was observed in the CuFe₂O₄ system with Cd doping. The line width and resonance field variation against change in temperature is noted and the data is fitted to the linearlized model (LM) and Smit and Beljers (SB) model to find out the parameters. The results recorded from the SB approach are in good agreement with those observed in the magnetic measurements carried out by vibrating sample magnetometer (VSM) techniques.     

The valence states of manganese ion in potassium-borate oxide glasses

EPR and magnetic susceptibility measurements have been performed on xMnO·(1-x) [2B₂O₃·K₂O] with 0?x?50 mol %. The X-ray diffraction analysis showed that in this glass system homogeneous glasses are formed up to x = 70 mol %.EPR and magnetic susceptibility data have shown that in the glasses with x ? 5 mol % only Mn²⁺ ions are present as magnetically isolated species. EPR spectra are modified with the increasing of manganese ions content. In the concentration range 0.5 ? x ? 5 mol %, the spectra are characterized by appearance of three resonance absorptions at g ? 4.3 and g ? 3.3 without hyperfine structure, and at g ? 2.0 with hyperfine structure. For the glasses with x >62; 5 mol %, the resonance spectra are characterized by the appearance of the broad line at g ? 2, characteristic for clustered ions. The magnetic susceptibility data suggest the appearance of superexchange interactions for x >62; 5 mol %. From Curie constant values and qualitative chemical analysis we have established that in the glasses with x ? 10 mol % both, Mn²⁺ and Mn³⁺ ions are present.     

Phase stratification in the Nd1 − x BaxCoO3 − δ (0.3 ≤ x ≤ 0.54) system

Slowly cooled Nd_{1 ? x} Ba_xCoO_{3 ? δ} samples were two-phase in the concentration interval 0.3 ≤ x ≤ 0.46. One of the phases had O-orthorhombic lattice distortions (Pbnm) characteristic of ferromagnetic samples with x ≤ 0.3, and the other phase had tetragonal distortions (P4/mmm) characteristic of samples with x ≥ 0.46. Tetragonal distortions were caused by ordering of Nd³⁺ and Ba²⁺ ions. Samples with ordered neodymium and barium ions (Nd_{1 ? y} Ba_{1 + y} Co₂O_{6 ? γ} at ?0.08 ≤ y ≤ 0.08) experienced metal-dielectric and orientation magnetic phase transitions.     

On the iron valence states in B2O3-PbO-GeO2 glasses

The Mössbauer effect measurements performed on 20Fe₂O₃ 80 3B₂O₃ (1?x)PbO xGeO₂ glasses show that the ratio between the number of ferrous ions to the total number of iron ions decreases by increasing the GeO₂ content. The Curie constants calculated from the distribution of iron cations obtained by Mössbauer effect data are in agreement with the values determined from magnetic measurements. Finally, we discuss the influence of the glass composition and melting temperature on the iron valence states.     

Magnetic properties of x • MnO • (1−x)[19TeO2 • PbO] glasses

The results of magnetic studies on x ? MnO ? (1 ? x)[19TeO₂ ? PbO] glasses are reported. The magnetic properties of these glasses are function of MnO content. For glasses with x > 5 mol% MnO, an antiferromagnetic behaviour is evidenced.     

Crystalline and magnetic structures of La1−x BixMnO3+δ manganites

The crystalline and magnetic structures and magnetic properties of La_1?x Bi_xMnO_3+δ (0.4 ≤ x ≤ 0.6, 0 ≤ δ ≤ 0.06) manganites have been studied. The solid solutions having the stoichiometric oxygen content are shown to be orbitally ordered A-type antiferromagnets. An increase in the oxygen content above the stoichiometric value is found to cause Mn⁴⁺ ions in the perovskite lattice, to remove the cooperative Jahn-Teller distortions, and to form a long-range ferromagnetic order. This order becomes broken as the concentration of the tetravalent manganese ions increases further. The tendency toward breaking the ferromagnetic order increases with the bismuth content. The magnetic properties are interpreted in terms of superexchange interactions on the assumption of local lattice distortions induced by anisotropy of the 6s ²(Bi³⁺)-2p ⁶(O^2?) chemical bonds.     

Magnetic microstructure of strontium-substituted thulium ferromanganites Tm0.65Sr0.35Mn1 ? x Fe x O3 (x = 0.3?0.4)

The structural and magnetic properties of the Tm_0.65Sr_0.35Mn_{1 ? x} Fe _x O₃ (x = 0.3?0.4) have been studied by methods of magnetic resonance and differential thermomagnetic analysis. A magnetic phase separation has been revealed in structurally single-phase samples.     

Magnetoresistive properties of Zn1−xCoxFe2O4 ferrites

The magnetic and magnetoresistive properties of spinel-type Zn_1−xCo_xFe₂O₄ (x=0, 0.2 and 0.4) ferrites are extensively investigated in this study. A large negative magnetoresistance (MR) effect is observed in Zn_1−xCo_xFe₂O₄ ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature, and show a spin-(cluster) glass transition at low temperatures, depending on the chemical compositions. The MR curves as a function of magnetic fields, MR(H), are parabolic at all temperatures for paramagnetic polycrystalline ZnFe₂O₄. The MR for ZnFe₂O₄ at 110 K in the presence of 9 T applied magnetic field is 30%. On the other hand, MR(H) are linear for x=0.2 and 0.4 ferrimagnetic Zn_1−xCo_xFe₂O₄ samples up to 9 T. The MR effect is independent of the sintering temperatures, and can be explained with the help of the spin-dependent scattering and the Yafet–Kittel angle of Zn_1−xCo_xFe₂O₄ mixed ferrites.     

Spin gap systems: What can be measured by muon spin relaxation?

Muon spin relaxation (μSR) and nuclear magnetic resonance (NMR) are powerful probes of magnetism, which have been extensively applied to studies of spin gap systems. Comparison of results obtained with the two techniques gives complementary results, as each is sensitive to different aspects of spin gap magnetism. We discuss recent μSR measurements of the spin ladder compounds Sr _n?1Cu _n+1O_2n , pure and doped Haldane materials (Y_2?x Ca _x )Ba(Ni_1?y Mg _y )O₅, and doped spin Peierls compounds (Cu_1?x Zn _x )(Ge_1?y Si _y )O₃.     

Spin state and magnetic interaction of cobalt ions in niobium-doped cobaltites

The magnetic properties and electrical conductivity of La_1?x Sr_xCo_1?x/2Nb _x/2O₃ solid solutions with trivalent cobalt ions are studied. These solid solutions are found to be spin glasses with T _f ～ 25 K. The ferromagnetic component is most pronounced in the composition with x = 0.15. The electrical conductivity decreases with increasing strontium content. The results obtained are interpreted within a model according to which cobalt ions located in the vicinity of strontium ions reside in an intermediate-spin state and the Co³⁺-O-Co³⁺ super-exchange interaction is ferromagnetic because of the local dynamic orbital correlations.     

Phase boundary between uniaxial and planar ferromagnets in layered perovskite manganite La2−2xSr1+2xMn2O7 (0.313⩽x⩽0.350)

We have examined magnetizations as a function of temperature and magnetic field in layered perovskite manganites La_2−2xSr_1+2xMn₂O₇ single crystals (x=0.313, 0.315, 0.318, 0.320 and 0.350) in order to determine the phase boundary between two ferromagnets (one is an uniaxial ferromagnet whose easy axis is parallel to the c-axis and the other is a planar ferromagnet whose easy axis is within the ab-plane) and following results are obtained: (i) all the present manganites exhibit magnetic transitions from a ferromagnet to a paramagnet at 76, 107, 116, 120 and 125 K for x=0.313, 0.315, 0.318, 0.320 and 0.350, respectively; (ii) for x=0.318, 0.320 and 0.350, the magnetic structure is a planar ferromagnet below Curie temperature; (iii) for x=0.313 and 0.315, the magnetic structure changes from an uniaxial to a planar ferromagnet at 66 and 85 K, respectively. From the results described above we have constructed the magnetic phase diagram of layered perovskite manganite La_2−2xSr_1+2xMn₂O₇ (0.313?x?0.350).