Co-substituted Samples Research Articles

Exchange coupled R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd,Pr) and Sm2(Fe,Co,Cr)17C2/(Fe,Co) nanocomposite magnets

Abstract Fe-rich exchange coupled nanocomposite R 8 (Fe,Co,Nb) 86 B 6 (R=Nd, Pr) (consisting of hard 2:14:1 and soft α-Fe(Co) phases) and Sm 2 (Fe,Co) 15 Cr 2 C 2 magnets (consisting of hard 2:17 and soft α-Fe(Co) grains) have been studied. In both systems the nanocomposite hard/soft microstructure is obtained by crystallizing the as-made amorphous melt-spun ribbons. The coercivity is found to depend mainly on the grain size of the soft phase which is very sensitive to the sample composition and annealing conditions. In the R–(Fe,Co,Nb)–B system, it is found that substitution of Nb for Fe significantly decreases the grain size of the α-Fe(Co) and increases the coercivity of the magnets. Substitution of Co for Fe increases the grain size and results in a dramatic decrease of coercivity. Increasing the B content of Co-substituted samples leads to a partial recovery of the coercivity. Magnetic properties M r / M s =0.7 and H c =6.5 kOe have been obtained for Pr 8 ((Fe 0.5 Co 0.5 ) 0.94 Nb 0.06 ) 82 B 10 . In the Sm 2 (Fe,Co) 15 Cr 2 C 2 system, it is found that a higher annealing temperature combined with a shorter annealing time leads to a higher coercivity. The optimum annealing condition is at 900°C for 1 min where the highest coercivity of 12.1 kOe is obtained. The grain size of α-Fe in annealed ribbons becomes much smaller with Co substitution, leading to a stronger exchange coupling between the 2:17 and α-Fe phase. A significant enhancement in the Curie temperature of the 2:17 phase is observed in these magnets as compared to their parent alloys due to the exchange coupling effect between the 2:17 phase and the Fe(Co) phase.

Suppression of superconductivity in Sm and Co substituted Bi 2Sr 2Ca 1Cu 2O 8+ δ system

The present work investigates the effect of Sm and Co substitution in Bi 2Sr 2Ca 1Cu 2O 8+ δ system. The substitution of Sm leads to an initial increase of transition temperature followed by a decrease. No such increase of transition temperature is observed in Sm and Co co-substituted samples, thus reflecting localization of excess holes in these samples. The suppression of superconductivity in both kind of samples occurs due to hole filling and disorder effects. The insulating state of the samples is described by 3D variable range hopping of conduction mechanism with energy dependent density of states.

A structural study of chemical stability of (Y1?x Ca x)(Ba2?x La x )Cu3O7??(x= 0.0, 0.2, and 0.4)

Neutron structural studies are made on (Y1−xCax)(Ba2−xLa x )Cu3O7−δ for compositions corresponding to x=0.0, 0.2, and 0.4 in order to evaluate any correlation between the remarkably high chemical stability of the cosubstituted samples (x=0.2 and 0.4) and the structural parameters. It is suggested that the increased chemical stability is caused by a decrease in the puckering of the Cu-O planes with increase inx, causing them to flatten, which leads to a reduction in the internal stresses existing in the perovskite lattice of this technologically important material.

Neutron scattering study of antiferromagnetic correlations in CeNi 1− xCo xSn

Magnetic excitation spectra in CeNi 1− x Co x Sn ( x = 0,0.1) have been studied by single-crystal neutron scattering. The inelastic peak at h ̵ ω = 4 meV and Q = (Q a, 1 2 + n, Q c) , which was observed in CeNiSn so far, was found to be suppressed, but could be detected in CeNi 0.9Co 0.1Sn. This suggests that the corresponding dynamic antiferromagnetic correlation still remains in the gap-suppressed Co-substituted sample.

Ｃｏ‐置換ＹＢａ２Ｃｕ３Ｏ７−ｄ超伝導体のラマン分光法による評価 ラマン分光法の高温超伝導体への応用 （１）

We have investigated the phonon Raman spectra of YBa2Cu3-xCoxO7-d ceramic samples prepared by a polymerized complex method using Raman microprobe collection optics. Defect induced Raman scattering from Cu(1)-O(1) chains has been observed in Co-substituted samples, suggesting that Co predominantly enters the chain site. With increasing Co content the frequencies of the Ba, Cu(2), 0(2)-0(3) and the apex oxygen 0(4) vibrational modes along caxis change considerably. The changes are compared with those of interatomic bond distances as obtained by neutron diffraction and they indicate charge transfer effects between the CuO chain and the CuO2 planes with increasing Co substitution. It is suggested that the O(4) mode is sensitive to small changes of the charge balance between the chain and the plane.

Variation of YBa 2(Cu 1−yCo y) 3O 6+x symmetry at constant stoichiometry: Relation with superconducting properties.

We performed heat treatments (800–830 °C) in inert atmosphere followed by oxidation at low temperature (400 °C) on Co-substituted YBa 2(Cu 1−yCo y) 3O 6+x, leading to the stabilization of the orthorhombic phase beyond y = .025. For example, orthorhombic symmetry is obtained with y = .06 with twin boundaries spacings as large 1000Å. Our STEM data on and between twin walls, and the presence of diffuse crosses around spots of each orthorhombic individual indicate that Co clusters exist also inside the orthorhombic domains. The orthorhombic samples recover the tetragonal symmetry by heating in flowing O 2 at 600 °C for 30mn. They present the tweed-like structure and the same type of diffusion as for the native compounds. In order to have a better understanding of the correlations between the structural details and the superconducting properties, ac-suceptibility and dc-magnetization mesurements are being carried out. Our first results show that the middle of the transition of the 6% Co-substituted orthorhombic sample is at lower temperature than that of same sample before heat treatment.

Magnetic and structural properties of melt-spun rare-earth transition-metal intermetallics with ThMn12 structure

The magnetic and structural properties of melt-spun R8Fe84Ti8 with R=Nd, Sm, Dy, Gd and R8(Fe,Co)76[V(Mo)]16 with R=Nd, Sm have been studied with x-ray diffraction, transmission electron microscopy, and magnetic measurements. The tetragonal ThMn12-type structure was found in all alloys after annealing at about 700 °C. The Curie temperature (Tc) of the as-spun amorphous samples was in the range of 40–100 °C. Crystallized Nd8(Fe1−xCox)84Ti8 samples with the 1:12 structure have a Tc around 250 °C for x=0, reaching the value of 660 °C for x=0.5 and then decreasing again to 490 °C for x=1. ac susceptibility studies on Co-substituted samples showed magnetic transitions in the temperature range 100–200 K. The coercivity was found to be strongly dependent on the microstructure. The highest value of Hc (2 kOe) was obtained in Sm-Fe-Ti samples with a grain size about 500 Å. The upper value of Hc is low because of the presence of some α-Fe in crystallized ribbons.