Superparamagnetic properties of La1 − x Sr x Mn0.925Zn0.075O3 (x = 0.075, 0.095, and 0.115) lanthanum manganites

Lanthanum-strontium manganites doped with zinc are studied by the method of electron magnetic resonance. Nano-objects with ferromagnetically correlated spins, which behave themselves like superparamagnetic particles in the magnetic resonance spectrum, have been found in the paramagnetic phase. The temperature dependences of the resonance magnetic field and magnetic resonance linewidth for La_{1 ? x} Sr _x Mn_0.925Zn_0.075O₃ ceramic samples at temperatures ranging from 100 to 340 K have been analyzed on the basis of the Raikher-Stepanov theory of superparamagnetic particles. The magnetic moment, anisotropy field, and characteristic size of the regions of the ferromagnetically correlated spins have been determined.     

Microstructure and Mössbauer studies on magnetostrictive Tb0.3Dy0.7Fe1.95 − x Nb x (x = 0, 0.025, 0.05 and 0.075)

³⁵Cl NQR measurements were carried out between 77 and 209 K for 3-chlorothiophene, which has a glass transition in a stable crystalline state. An NQR signal with full widths of about 100 kHz at half maximum was observed in this temperature range. The spin-lattice relaxation time T ₁ was measured at the peak frequencies. The activation energy Δε _a obtained from the results of the T ₁ measurements showed a good agreement with those estimated from calorimetric measurements.     

Electrical,magnetic, and thermal properties of UCu5− x Pt x

We report measurements of the structural and electronic properties of UCu_{5??? x} Pt _x , a Pt-based analogue of the nFL system UCu_{5??? x} Pd _x , in the concentration range 0≤?x?≤?5. Forx?≤?2.5 and x?≥?4.5, the UCu_{5??? x} Pt _x system crystallizes in the AuBe₅ structure, but is mixed phase in the range 2.5?<?x?<?4.5. We observe a rapid suppression of long range antiferromagnetic order for small concentrations of Pt. The electrical resistivity, DC magnetic susceptibility, and specific heat of UCu_{5??? x} Pt _x in the concentration range 0.75?≤?x?≤?1 have temperature dependencies at low temperature (T?≤?10?K) consistent with the non-Fermi liquid behaviour found in UCu_{5??? x} Pd _x . Above x?=?1, there is a transition from non-Fermi liquid behaviour to Fermi liquid behaviour with no observation of any spin glass behaviour.     

The crystallization of Fe1−x P x , 0.09≦x≦0.26

The crystallization behaviour of about 60 samples of electrodeposited Fe_1–x P _x , 0.09<x<0.26, was investigated with DSC and X-ray diffraction. Several subsequenting transformations during heating at 10 K/min were identified. The corresponding transformation temperatures, reaction heats and reaction rates were measured. If the as-deposited samples contain metal-rich crystallites (microcrystalline and partly amorphous material) crystallization starts with primary precipitation of -iron followed by polymorphous crystallization of Fe₃P. In amorphous samples these two processes become less important compared with the eutectoid reaction the higher the phosphorus content. In a small concentration range around 19 at% P this transformation is the only one. Above this range the primary crystallization of Fe₃P becomes more and more dominant.     

Phase formation and dielectric properties of (Pb0.925Ba0.075)(Zr1− x Ti x )O3 ceramics prepared by the solid-state reaction method

Lead barium zirconate titanate [(Pb_0.925Ba_0.075)(Zr_{1? x} Ti _x )O₃] ceramics with 0?≤?x?≤?1 were prepared by the solid-state reaction method. The calcination temperatures were between 800°C and 1000°C for 1?h and the sintering temperature was 1200°C for 3?h. It was found that the structure of the calcined powders and sintered pellets was in an orthorhombic phase for x?=?0; a rhombohedral phase for x?=?0.25 and a tetragonal phase for 0.5?≤?x?≤?1. The c/a ratio increased with an increase in the x content. The average particle size and density slightly decreased with an increase in the x content, while the average grain size, linear shrinkage, and Curie temperature increased when the x content increased.     

Lattice,electrical, and magnetic effects in lanthanum manganites La1−x Sr x MnO3 (x = 0.125, 0.150, 0.175)

The temperature dependences of the velocities of transverse and longitudinal hypersound in lanthanum strontium manganites of the composition La_1−x Sr _x MnO₃ (x = 0.125, 0.150, 0.175) have been measured at frequencies of 0.5–0.7 GHz. The structural phase transitions have been revealed, and their positions have been confirmed by data on the electrical resistance and magnetic measurements performed using the same samples. The results obtained have been analyzed in the framework of the model of competing Jahn-Teller distortions and magnetic ordering. The anomalies observed in the behavior of the velocities of longitudinal hypersound have been attributed to the local Jahn-Teller distortions, and their suppression due to the magnetic ordering has been considered a possible factor responsible for the colossal magnetoresistance.     

Optical spectroscopy and electronic structure of compounds HoNi5 − x Al x (x = 0, 1, 2)

The optical properties of the compounds HoNi_{5 ? x} Al _x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined.     

Electron work function in YNi3 − x T x (T = Cu,Fe, Mn; x = 0, 0.5) intermetallics

The electron work function in cast samples and cylindrical compacts of YNi_{3 ? x} T _x (T = Cu, Fe, Mn; x = 0, 0.5) intermetallics is determined using the contact potential difference method. A correlation is found between the electron work function and the electronegativity of elements substituting Ni in the YNi₃ structure.     

Magnetism influenced by structural disorder in melt-spun DyMn6 − x Ge6 − x Fe x Al x (x = 2.5, 3)

Different chemical and/or geometrical orders were found in melt-spun DyMn_6???x Ge_6???x Fe _x Al _x with x = 2.5 and 3 having fully amorphous and mixed (crystalline and amorphous) structure, respectively. Thermal variations in magnetization M from liquid helium up to room temperature for both samples are similar. Magnetization value at zero field cooled curve reaches about 0.1 μ_B per formula unit at 2 K and then increases. Two maxima are visible, the first at 50 K (a sharp effect) and the second very broad ranging from 150 to 200 K. ⁵⁷Fe Mössbauer spectrometry investigation revealed a remaining magnetic component in addition to a prevailing quadrupolar feature. Application of a weak external magnetic field causes an increase in the mean hyperfine magnetic field B _hyp and the volume fraction of magnetic component. This observation was confirmed by results of M(T), M(H) and AC magnetic susceptibility measurements. In short-range ordered crystallographic zones characteristic of melt-spun DyMn_6???x Ge_6???x Fe _x Al _x (x = 2.5, 3) alloys, the related magnetic ordering, called the mictomagnetism or the cluster spin glass appears.     

Glass transition,thermal stability and glass-forming ability of Se90In10− x Sb x (x = 0, 2, 4, 6, 8, 10) chalcogenide glasses

Differential scanning calorimetry (DSC) has been employed to investigate the glass transition activation energy E _g, thermal stability and glass-forming ability (GFA) of Se₉₀In_{10? x} Sb _x (x = 0, 2, 4, 6, 8, 10) chalcogenide glasses. DSC runs were performed at six different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperature. The dependence of glass transition temperature T _g on heating rate (α), as well as composition of Sb, has been studied. From the dependence of glass transition temperature on heating rate, the E _g has been calculated on the basis of the Kissinger [Anal. Chem. 29 (1957) p.1702] and Moynihan [J. Phys. Chem. 78 (1974) p.267] models. Thermal stability has been monitored through the calculation of temperature differences T _c–T _g, the stability parameter S, and the enthalpy released during crystallization H _c. The GFA has been investigated on the basis of the Hruby parameter H _r, which is strong indicator of GFA. Results for GFA are in good agreement with fragility index F _i calculations, indicating that Se₉₀In₆Sb₄ is an excellent glass-former.     

Magnetic properties, magnetoresistance, and Raman spectra of CuV x Cr1 − x S2

The results of investigations of the magnetic and Raman spectra, magnetic properties, and magnetoresistance of vanadium-substituted chromium copper disulfides CuV _x Cr_{1 ? x} S₂ (x = 0.1) are presented.     

Structural phase transitions in Cu2–x Te crystals (x = 0.00, 0.10, 0.15, 0.20, 0.25)

Structural phase transitions in Cu_2–x Te crystals have been investigated by high-temperature X-ray diffraction.

At room temperature Cu₂Te and Cu_1.90Te specimens are two-phased, i.e. they consist of an orthohombic phase with a = 7.319, b = 22.236, c = 36.458 Å and a hexagonal phase with a = 4.150, c = 7.188 Å. The changes in both compounds take place generally in the hexagonal phase with increasing temperature. At 821, 873 K they transform to a FCC phase. Monocrystals of the other compounds at room temperature crystallize in the hexagonal system and at 673, 773, 723 K, respectively, they transform to a FCC phase. It is determined that as the cation deficiency increases the crystal quality becomes better.     

Study of electrochemical performances of multi-doped spinel Li1.1Mn1.85Co0.075Ni0.075O4 at 4.3 and 5 V

Li_1.1Mn_2???2x Co _x Ni _x O₄ (x?=?0, 0.075) spinel powders were successfully synthesized using a liquid stirred tank reactor method. The electrochemical performances of the undoped and doped spinels at 4.3 and 5 V were investigated by X-ray diffraction, field-emission scanning electron microscopy, and electrochemical impedance spectroscopy. The capacity of Li_1.1Mn_2???2x Co _x Ni _x O₄ could be divided into two parts, with 4.3 V as the dividing line in the 3–5 V charge–discharge range. Low capacity and good cyclic performance were obtained when cycled in the 3–4.3 V range for the multi-doped Li_1.1Mn_2???2x Co _x Ni _x O₄ spinel. In comparison with multi-doped spinel at 4.3 V, the results of the cyclic performance worsened at 5 V because the structure underwent further shrinkage, the charge transfer resistance rose and the electrolyte decomposed.     

Electron spin resonance study of the dynamic magnetic susceptibility of CuO, Cu1−x Zn x O, and Cu1−x Li x O single crystals

Results are presented of studies of the dynamic magnetic susceptibility of CuO, Cu_1?x Zn _x O (x ≈ 1.5%), and Cu_1?x Li _x O (x ≈ 1%) single crystals. The orientational dependence of the ESR spectra was investigated at room temperature. The results for CuO are analyzed using a model of a quasi-one-dimensional antiferromagnet (S = 1/2) with anisotropic exchange interaction between Cu²⁺ spins in the chains and exchange coupling between the chains allowing for one-dimensional spin diffusion and spinon excitations. The estimated line width is of the same order of magnitude as the experimental data. Substituting Cu with Zn scarcely alters the spin dynamics of the Cu²⁺ ions, as in weakly diluted magnets. Lithium doping substantially increases the ESR line width and this is attributed to excess holes forming rapidly relaxing spin complexes with copper ions.     

Cluster glass-like behavior of the diluted antiferromagnet Fe x Mg1−x TiO3 (x=0.2,x=0.3)

A diluted antiferromagnet Fe _x Mg_1–x TiO₃ has been shown to behave as a spin glass (x=0.2) and a reentrant spin glass (x=0.3) near the Fe percolation concentrationx 0.25. In order to obtain microscopic information on these samples, we performed Mössbauer measurements. At considerably higher temperatures than the transition temperatures, magnetically broadened spectra appear superimposed upon the paramagnetic doublets. A remarkable feature is that the intensity of the magnetic spectra increases accompanying the decrease of their linewidth. This behavior can be ascribed to the gradual slow-down of fluctuations of the antiferromagnetic clusters formed at high temperatures. To investigate the temperature variations of the relaxation time of the clusters, we analyzed the Mössbauer spectra using the method formulated by Blume. It has been shown that becomes long with decreasing temperature and the rate of the slow-down of is hastened aroundT _SG andT _N.     

Temperature hysteresis of magnetic phase transitions in Tb1 − x Ce x Mn2O5 (x = 0, 0.20, 0.25)

The temperature evolution of the magnetic structure of multiferroics Tb_{1 ? x} Ce _x Mn₂O₅ (x = 0, 0.20, 0.25) has been investigated using the neutron scattering methods. It has been found that, despite the qualitative similarity of the magnetic states and the series of phase transitions for pure TbMn₂O₅ (TMO) and doped crystals Tb_{1 ? x} Ce _x Mn₂O₅ (TCMO, x = 0.20 and 0.25), there are significant differences in their properties. In contrast to TMO, where there are three magnetic phases, TCMO can include two magnetic phases that coexist in a wide temperature range and exhibit a rather wide temperature hysteresis. One of these phases with wave vector k ₁ = (0.5, 0, k _z1), k _z1 = 0.25, is commensurate and arises at temperatures below T _N ～ 39 K (for x = 0.2) and T _N ～ 38 K (x = 0.25). The second phase is incommensurate with wave vector k ₂ = (1/2, 0, k _z2), k _z2 = 0.256(2), and appears upon cooling at T = 21 K (x = 0.2) and T = 19 K (x = 0.25). Upon further cooling to 16 K, the component k _z2 increases to 0.292(2) and then remains constant. The component k _z1 increases to the value of 0.280(2) upon cooling in the range from 15 to 10 K and then remains constant down to 1.5 K. With an increase in the temperature, the components k _z1 and k _z2 undergo reverse changes to their initial values, but these changes occur at temperatures 7 K higher than those observed with a decrease in the temperature. For TMO, two phases also coexist, but the temperature hysteresis in this case is considerably smaller than for TCMO. This is explained by different densities of domain walls and different sizes of domains in pure and doped crystals.     

Oxygen non-stoichiometry, redox thermodynamics, and structure of LaFe1 − x Co x O3 − δ

The oxygen non-stoichiometry and redox thermodynamic properties of the LaFe_{1 ? x} Co _x O_{3 ? δ} system (x?=?0.25 and 0.75) are studied. At low temperatures, the LaCoO₃ and LaFeO₃ systems show partial solid solubility. At 1,273 K (in air), both compounds are single phases and are orthorhombic and rhombohedral for x?=?0.25 and 0.75, respectively. Thermogravimetry has been used to measure the oxygen non-stoichiometry versus oxygen partial pressure at three temperatures, 1,223, 1,273, and 1,323 K. Redox thermodynamic quantities are extracted directly from the oxygen non-stoichiometry curves. The extracted enthalpies of oxidation do not vary significantly with stoichiometry, and for x?=?0.25 and 0.75, they are ?640?±?60 and ?440?±?60 kJ (mol O₂)^?1, respectively. Ideal solid solution thermodynamic models are used to analyze the redox mechanisms.     

Superconductivity,crystallization, and structural relaxation of the new metallic glass system La1−x Si x (0.15≤x≤0.27)

New metallic glass alloys have been prepared by melt spinning of La–Si samples in a pumped system. The superconducting transition temperature,T _c , increases linearly with the La concentration, from 3.00 K at 73 at. % La to 3.80 K at 85 at. %. Three new metastable phases: -, -, and -La₃Si, were formed by annealing and crystallizing amorphous La₃Si. Their crystal structures are orthorhombic (a=6.32 Å,b=8.06 Å,c=9.96 Å), hcp (a=10.55 Å,c=5.05 Å), and tetragonal (a=6.92 Å,c=5.05 Å) resp.T _c increased to 3.75 K, 6.00 K and 6.80 K, resp. During low temperature anneals of an amorphous La₃Si alloy,T _c changed logarithmically with time.On leave from Institute of Physics, Academica Sinica, Beijing, China     

High-temperature background of internal friction in (Co45Fe45Zr10) x (Al2O3)100 − x , Co x (CaF2)100 − x , and Co x (PZT)100 − x nanocomposites

The elastic (G) and inelastic (Q ^?1) properties of (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 ? x} , Co _x (CaF₂)_{100 ? x} , and Co _x (PZT)_{100 ? x} (x = 23–76 at %) nanocomposites obtained by ion-beam sputtering are studied in the temperature range 300–900 K. A significant rise in the Q Q ^?1 (T) curve is observed at temperatures above 650 K, which is attributed to thermally activated migration of point defects under the conditions of confined geometry.     

Mössbauer study of intergranular phase in Nd 8 Fe86 − x Nb x B6(x = 0, 1, 2, 3) nanocomposite magnet

Nd₈Fe_86???x Nb _x B₆ (x = 0, 1, 2, 3) nanocomposite magnet has been studied by Mössbauer spectroscopy and nanostructure observation. It was found that intergranular phase formed between α-Fe and Nd₂Fe₁₄B phase in NdFeNbB alloys plays a significant role on the magnetic properties. By the addition of Nb into Nd₈Fe₈₆B₆ composition, coercivity was found to increase by 25% due to the grain refinement of both the soft and hard magnetic phases which was decreased from 50 nm of virgin Nd₈Fe₈₆B₆ to 25 nm in Nd₈Fe₈₅Nb₁B₆ alloys. The role of Nb addition was confirmed to stabilize the Nd₂Fe₁₄B lattice preventing from thermal vibration of the corresponding sites at where Fe atoms are substituted by Nb in the Nd₂Fe₁₄B lattice. The enhanced coercivity was originated from the exchange hardening of soft and amorphous phases surrounding the hard magnetic Nd₂Fe₁₄B crystal.