On the appearance of ferromagnetism in Y(Co1−xAlx)2 alloys

The appearance of ferromagnetism in Y(Co_1−xAl_x)₂ is discussed in terms of a d band model. The approximate d bands for YCo₂ and Y(Co_1−x)₂ are calculated and the decrease in the electronic energy due to magnetization of the spin of estimated. The energy decrease is the largest in YCo₂, and it gradually decreases as the Al content increases, if the lattice constant is fixed, while this energy decrease increases if the lattice constant increases with increasing Al content. These results of calculations give a good account of the appearance of ferromagnetism in Y(Co_1−xAl_x)₂ around x = 0.15. The ferromagnetism in Sc(CO_1−xAl_x)₂ is also discussed, leading to the appearance of ferromagnetism between x = 0.15 and 0.30.     

The anomalous behaviour of Gd atoms (Fe1−xMnx)2 compounds

The educed Gd atoms in the X-structure (Th₆Mn₂₃-type) of Gd(Fe_1−xMn_x)₂ were magnetically investigated by comparing with Gd₆(Fe_1−yMn_y)₂₃ whose structure is Th₆Mn₂₃-type. The magnetic properties of Gd(Fe_1−xMn_x)₂ (0.4≤x≤0.7) were observed to be quite similar to those of Gd₆(Fe_1−yMn_y)₂₃ (0.4≤y≤0.7).     

Thermoelectric power of Y(Mn1−xAlx)2

Electrical resistivity and thermoelectric power of Y(Mn_1−xAl_x2 and (Y_1−xSc_x)Mn₂ were measured from 2 to room temperature. Anomalous behavior of the thermoelectric power of YMn₂ disappears rapidly with the increase of Al content in Y(Mn_1−xAl_x)₂. Based upon spin fluctuations of the itinerant antiferromagnetism of the samples, the anomaly of the thermoelectric power is discussed.     

The order of magnetic phase transition in La(Fe1−xCox)11.4Si1.6 compounds

Magnetic transitions in La(Fe_1−xCo_x)_11.4Si_1.6 compounds with x=0–0.08, have been studied by DC magnetic measurements and Mössbauer spectroscopy. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization, M(μ₀H), using the Landau expansion of the magnetic free energy. For x0.02 there is a strongly first-order magnetic phase transition between ferromagnetic and paramagnetic (F–P) states in zero external field and a metamagnetic transition from paramagnetic to ferromagnetic (P–F) above T_c. Increasing the cobalt content drives the F–P transition towards second order and eliminates the metamagnetic transition.     

Temporary phase segregation processes during the oxidation of (Fe0.7Mn0.3)0.99O in N2---H2O atmosphere

A two-step thermochemical cycle with the ternary metal oxide system (Fe_{1 − x}Mn_x)₃O₄/(Fe_{1 − x}Mn_x)_{1 − y}O is applied to convert solar energy to chemical energy. Experimental investigations on the water splitting reaction of (Fe_{1 − x}Mn_x)_{1 − y}O revealed temporary formation of a manganese rich rock salt phase and an iron rich spinel phase due to phase segregation processes.     

High field magnetization of the Laves phase compounds M(Co1−xAlx)2 (M = Y, Lu)

Magnetization measurements have been carried out on the Laves phase compounds M(Co_1−xAl_x)₂(M = Y, Lu) up to 42 T. Sharp metamagnetic transitions with small hysteresis are found in Y(Co_1−xAl_x)₂, while broad transitions with large hysteresis are found in Lu(Co_1−xAl_x)₂. The results suggest that the former compounds are magnetically homogeneous but the latter inhomogenous.     

Magnetization measurements of Fe1−xCoxSi

Magnetization measurements are made in pulsed magnetic fields up to 200 kOe at 4.2 K and up to 100 kOe at various temperatures on the alloys Fe_1−xCo_xSi. In the paramagnetic region of x<0.05 or x0.7, we expected a metamagnet transition at high field but no remarkable change of magnetization is observed.     

Temperature dependence of induced magnetic anisotropy in metallic glasses (Fe1 − xCox)78Si10B12

The variations of induced magnetic anisotropy with annealing and measuring temperatures in metallic glasses (Fe_{1 − x}Co_x)₇₈Si₁₀B₁₂ have been measured. It was found that K_u (T) was proportional to Mⁿ_s (T) for T below 200°C, and the index n varied with the cobalt content x and annealing conditions, not being smaller than 3. To the predictions of the existing pair-ordering and single-ion theories, the above results are anomalous. By considering the distributions of exchange integrals and activation energies in metallic glasses, this anomalous behaviour could be explained properly.     

Spin fluctuations of Y(Mn1−xAlx)2 and Y1−xScxMn2

The thermal expansion and low temperature and low temperature specific heat were measured for Y_1−xScxMn2. The results are discussed in terms of spin fluctuations and compared with those of Y(Mn_1−xAl_x)₂, which show al local moment character. It is revealed that Y_1−xSc_xMn₂ is a typical nearly antiferromagnet in which giant spin fluctuations are thermally excited.     

Spin fluctuations in weakly itinerant ferromagnets Y(Co1−xAlx)2

The nuclear spin-lattice relaxation rate, 1/T₁, has been measured in weak itinerant ferromagnets Y(Co_1−xAl_x)₂. The temperature and magnetic field dependence of 1/T₁T has been found to be well described by the self-consistent renormalization (SCR) theory of spin fluctuations. The parameters characterizing spin fluctuations in this system were estimated from NMR and magnetic measurements. The temperature dependence of susceptibility calculated from these parameters well reproduces the experimental results.     

Magnetic moments and Fe hyperfine field interactions in Y(Fe1−xRux)2 ternaries

Measurements of magnetization and ⁵⁷Fe Mössbauer spectra have been made for Y(Fe_1−xRu_x)₂. The C15 type cubic structure is stabilized for xx 0.7. The C15 compounds is ferromagnetic with T_c200 K and its saturation moment decreases monotonically with increasing x, while the ⁵⁷Fe hyperfine field decreases only slightly with x. From these results, it is deduced that the Ru atoms have an induced moment of ≈1μ_B in the range x 0.2. In the C14 type phase, no magnetic ordering develops even at 4.2 K.     

Hyperfine fields at Y nuclei in Y(Fe1−xTx)3 (T = Al, Co)

The spin echo spectra of ⁸⁹Y hyperfine fields in Y(Fe_1−xT_x)₃ with low concentration x consist of two main lines and of satellite lines caused by the replacement of the Fe atoms by the T atoms. Values of the magnetic moments of the T atoms are estimated by observing the satellite lines.     

Study on the superconducting composite material formation in the system Bi2Sr2CaCu2O8+x/Al-containing phases

Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr_1.5Ca_0.5Al₂O_z and (Sr_1−xCa_x)₃Al₂O₆ (x = 0.4 − 0.45) were determined to be chemically compatible with Bi_2.18Sr₂CaCu₂O_8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr_1.5Ca_0.5Al₂O_z was found to be in equilibrium only with the melt and the (Sr_1−xCa_x)₃Al₂O₆ phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr_1.5Ca_0.5Al₂O_z ↔ (Sr_1−xCa_x)₃Al₂O₆ + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr_1.5Ca_0.5Al₂O_z and Bi-2212 + m(Sr_1−xCa_x)₃Al₂O₆ were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr_1.5Ca_0.5Al₂O_z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr_1−xCa_x)₃Al₂O₆ imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr_1−xCa_x)₃Al₂O₆ materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.     

Co含量对Fe3Si合金磁学性能的影响

采用基于密度泛函理论（DFT）的赝势平面波法,对过渡金属Co掺杂Fe₃Si进行几何结构优化,计算Co含量对Fe₃Si合金磁学性质的影响.研究表明：Fe_3-xCo_xSi的磁性主要来源于过渡金属元素Fe和Co,并且相对于A、C位的Fe和Co原子,B位Fe的原子磁矩较大;在0≤x≤0.75范围内,随着Co含量的增大,Fe_3-xCo_xSi的总磁矩缓慢减小,在0.75≤x≤1.5时,其总磁矩迅速地增大;A、C位Fe原子的磁矩和合金总磁矩的变化趋势相同,Co原子的磁矩随着Co含量的增大缓慢地增大,原子的磁矩变化与自旋向上和向下方向的电荷转移有关.     

Cobalt substituted R---Fe(Co)---C alloys

The formation of tetragonal R₂(FeCo)₁₄C phase has been examined in as-cast and melt-spun R₁₄Fe_78−xCo_xC₈ alloys with cobalt substitutions (R = Y, Dy, Nd). The magnetic properties over a temperature range and the microstructure have been studied as a function of cobalt content. The Curie temperature is increased with Co content but the anisotropy K is decreased. High cobalt content leads to the formation of 1:5 phase. High corecivities have been developed in as-cast and melt-spun Dy₁₄Fe_78−xCo_xC₈ alloys with Co content at zero and 32 at %, respectively. As-cast Nd₁₆Fe_78−xCo_xC₈ alloys did not show any permanent magnetic properties although they had the 2:14:1 phase. However, melt-spun and powdered Nd---Fe---Co---C samples showed a coercivity with the highest value corresponding to a melt-spun Nd₁₄Fe₇₈C₈ sample. Microstructure studies showed that the high H_C in ribbons is due to the fine grain size which is in the range of 500–1000 Å.     

Mixed electronic and ionic conductivity of LaCo(M)O3 (M=Ga, Cr, Fe or Ni).: V. Oxygen permeability of Mg-doped La(Ga, Co)O3−δ perovskites

The LaGa_1−x−yCo_xMg_yO_3−δ solid solutions with rhombohedrally-distorted perovskite structure were ascertained to form in the concentration range of 0≤y≤0.10 at x=0.60 and 0≤y≤0.20 at x=0.35–0.40. Increasing cobalt content results in increasing electrical conductivity and thermal expansion of the perovskites. Thermal expansion coefficients of the LaGa_1−x−yCo_xMg_yO_3−δ ceramics were calculated from the dilatometric data to vary in the range of 12.4–19.8×10⁻⁶ K⁻¹ at 300–1100 K. Doping La(Ga,Co)O_3−δ solid solutions with magnesium leads to increasing oxygen nonstoichiometry, electronic and oxygen ionic conductivity. Oxygen permeation fluxes through LaGa_1−x−yCo_xMg_yO_3−δ membranes were found to be limited by the bulk ionic conduction and to increase with magnesium concentration, being essentially independent of cobalt content.     

Oxygen permeability of La2Cu(Co)O4+δ solid solutions

Formation of the La₂Cu_1−xCo_xO_4+δ solid solutions with orthorhombic K₂NiF₄-type structure was found to be in the range of 0≤x≤0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La₂Cu_1−xCo_xO_4+δ (x=0.02–0.30) ceramics at 470–1100 K were calculated from the dilatometric data to vary in the range (12.2–13.2)×10⁻⁶ K⁻¹. Studying the dependence of oxygen permeation fluxes through La₂Cu(Co)O_4+δ on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La₂Cu_1−xCo_xO_4+δ solid solutions was ascertained to increase with cobalt concentration at x=0.02–0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport.     

Origin of enhanced coercivity in (Fe65Co35)x(Al2O3)1-x granular thin films

The magnetic behaviors of granular (Fe₆₅Co₃₅)_x(Al₂O₃)_1−x films have been examined. The results show that the coercivity at 5 K first increases sharply from 80 Oe for x = 0.1 to 700 Oe for x = 0.3 and then drops with increasing x. This behavior differs from the system of Fe-SiO₂. Considering the interfacial area, we can theoretically explain the difference between these systems. It is concluded that the peak value of coercivity becomes smaller and occurs at a lower value of x for a more rapidly increasing granular size with volume fraction.     

Magnetic characteristics of R2(Fe, Co)14B systems (R = Y, Nd and Gd)

R₂(Fe, Co)₁₄B compounds (R = Y, Nd and Gd) were prepared in high purity. The magnetic behavior of R₂(Fe, Co)₁₄B compounds is reported over the temperature range 4 to 300 K. The effects of Fe substitution by Co on the saturation magnetization, Curie temperature and anisotropy are presented. The spin-reorientation temperature is lowered as Co replaces Fe. This also results in a reduced cone angle.

The R₂Fe_14−xCo_xB alloys crystallize in the tetragonal structure over the entire concentration range of 0 x 14. When Fe is substituted by Co, the Curie temperature increases significantly, the saturation magnetization increases to a maximum value around x = 2, and the anisotropy becomes planar for R = Y and Gd. The Nd₂(Fe, Co)₁₄B systems all exhibit uniaxial anisotropy at room temperature and Nd₂Co₁₄B is strongly uniaxial at 77 K. The Nd₂(Fe, Co)₁₄B systems are conical at 77 K.     

Effects of cation- or oxide ion-defect on conductivities of apatite-type La–Ge–O system ceramics

A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In La_xGe₆O_12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, La_x(GeO₄)₆O_1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La₉(GeO₄)₆O_1.5 (x=9), where the number of cation (La³⁺) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La_9−0.66xSr_x(GeO₄)₆O_1.5 (x=0–1), La_9−1.33xZr_x(GeO₄)₆O_1.5 (x=0–1), La_9−xSr_x(GeO₄)₆O_1.5−0.5x (x=0–3), La_9−xZr_x(GeO₄)₆O_1.5+0.5x (x=0–1), La_x(GeO₄)_3x−21(AsO₄)_27−3xO_1.5 (x=0–3), La_x(GeO₄)_33−3x(AlO₄)_3x−27O_1.5 (x=0–3), La₉(GeO₄)_6−x (AlO₄)_xO_1.5−0.5x (x=0–3), La₉(GeO₄)_6−x(AsO₄)_xO_1.5+0.5x (x=0–1), La_9.33−xSr_x(GeO₄)₆O_2−0.5x (x=0–1.2) and La_x(GeO₄)_4.5(AlO₄)_1.5O_1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La³⁺and GeO₄⁴⁻of the basic apatite La₉(GeO₄)₆O_1.5 with Sr²⁺ or Zr⁴⁺ and AlO₄⁵⁻ or AsO₄³⁻. Such substitutions lowered the conductivity of La₉(GeO₄)₆O_1.5. These results were discussed by the electrostatic interaction between Sr²⁺, Zr⁴⁺, AlO₄⁵⁻ or AsO₄³⁻ and oxide ion as a conductive species.