Small Amount Of Co Substitution Research Articles

Anisotropic magnetic excitations and incipient Néel order in Ba(Fe1−xMnx)2As2

It is currently understood that high temperature superconductivity (SC) in the transition metal $(M)$ substituted iron arsenides Ba(Fe$_{1-x}$$M$$_{x}$)$_{2}$As$_{2}$ is promoted by magnetic excitations with wave vectors $(\pi,0)$ or $(0,\pi)$. It is known that while a small amount of Co substitution leads to SC, the same does not occur for Mn for any value of $x$. In this work, magnetic excitations in the iron arsenides Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x=0.0$, $0.007$, $0.009$, $0.08$) are investigated by means of Resonant Inelastic X rays Scattering (RIXS) at the Fe $L_{3}$-edge, for momentum transfer $\boldsymbol{q}$ along the high symmetry Brillouin zone $(\pi,0)$ and $(\pi,\pi)$ directions. It is shown that with increasing Mn content ($x$), the excitations become anisotropic both in dispersion and lineshape. Both effects are detected even for small values of $x$, evidencing a cooperative phenomenon between the Mn impurities, that we ascribe to emerging N\'eel order of the Mn spins. Moreover, for $x=0.08$, the excitations along $\boldsymbol{q}\parallel(\pi,0)$ are strongly damped and nearly non dispersive. This result suggests that phases of arsenides containing local moments at the FeAs layers, as in Mn or Cr substituted phases, do not support high temperature SC due to absence of the appropriate magnetic excitations.

Magnetic properties of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) and their nitrides

In this work, alloys of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) were prepared via arc melting and heat treatment. The nitrides of these alloys were synthesized using a gas-solid state reaction method. The influence of Co substitution for Fe in NdFe10.5Mo1.5 and NdFe10.5V1.5 alloys and their nitrides were investigated. It was found that the lattice parameters a, c, and unit cell volume V decrease with increasing Co content x for Nd(Fe1-xCox)10.5Mo1.5. As compared to their parent alloys, the lattice parameters and unit cells volume increase after nitrogenation, which gives rise to higher Curie temperature, magnetization and magnetocrystalline anisotropy field for nitrides. A small amount of Co substitution for Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides, due to the modification of the band structure by Co atom. As a result, Nd(Fe1-xCox)10.5Mo1.5Ny and Nd(Fe1-xCox)10.5V1.5Ny with x≤0.2 become promising candidates for permanent magnet applications. A coercivity of 4.6 kOe and maximum energy product BHmax of 20 MGOe were achieved for NdFe9.45Co1.05Mo1.5Nx.

Structural, magnetic and magnetoelastic properties of Laves-phase Tb0.3Dy0.6Nd0.1(Fe1-xCox)1.93 compounds (0 ≤ x ≤ 0.40)

Structure, magnetization and magnetostriction of Tb0.3Dy0.6Nd0.1(Fe1-xCox)1.93 (0 ≤ x ≤ 0.40) compounds have been investigated. X-ray diffraction (XRD) analysis shows the presence of single Laves phase with a cubic MgCu2-type structure. The easy magnetization direction (EMD) is observed to be <111> direction when x ≤ 0.10, and deviates away with further increasing Co contents. The Co contributes an opposite role in the resultant magnetocrystalline-anisotropy compared to Tb. A small amount of Co substitution for Fe can enhance the Curie temperature for x ≤ 0.25. The magnetocrystalline-anisotropy compensation can be achieved in this system. A minimum in anisotropy is obtained for the Tb0.3Dy0.6Nd0.1(Fe0.8Co0.2)1.93 compound, which has good magneto-elastic properties, e.g., the large saturation magnetostriction λS (∼930 ppm) and the high low-field magnetostriction λa (∼670 ppm/3 kOe), and may make it technological interest in the field of magnetostrictive materials.

Magnetic properties and magnetocaloric effect of Hf–Ta–Fe–(CO) alloys

The as-cast intermetallic compounds Hf0.8Ta0.2Fe1.98−xCox (x=0, 0.02 and 0.04) show a temperature or magnetic field induced first-order magnetic transition (FOMT) between aferromagnetic (F) and anantiferromagnetic (AF) state. The maximum magnetic entropy change (|ΔS|) is about 4.8J/kgK when x=0 in a magnetic field change of 5T. A small amount of Co substitution for Fe does not significantly reduce the maximum |ΔS| but broadens the working temperature range.

Microwave dielectric properties of low-loss (Zn1−xCox)3Nb2O8 ceramics for LTCC applications

The phase relation, crystal structure and microwave dielectric properties of (Zn1−xCox)3Nb2O8 ceramics were investigated. The limit of (Zn1−xCox)3Nb2O8 solid solutions was approximately x=0.4. With an increasing x, the corrected dielectric constant decreased and the temperature coefficient of resonant frequency (τf) increased. The τf value is strongly dependent on the tilting of the oxygen octahedral, which can be evaluated by the B-site bond valence. However, a tremendous loss reduction can be achieved by a small amount of Co substitution due to the increase in relative density and packing fraction. The B2O3 and CuO addition can effectively lower the sintering temperature of (Zn0.95Co0.05)3Nb2O8 without seriously deteriorating the dielectric properties. For LTCC applications, the 4wt% B2O3–CuO doped (Zn0.95Co0.05)3Nb2O8 ceramic sintered at 930°C is a good choices because of its excellent dielectric properties (ɛr∼20.75, Q×f∼105,000GHz and τf∼−83.7ppm/°C) and the chemical compatibility with silver.

Microwave dielectric properties of Nd[(Zn1−xCox)0.5Ti0.5]O3 (0.025 ≤ x ≤ 0.1) ceramics

Microwave dielectric properties of Nd[(Zn1−xCox)0.5Ti0.5]O3 (0.025≤x≤0.1) ceramics have been investigated. Solid solutions were formed for the ceramic system in the given compositional range. With x increasing from 0.025 to 0.1, dielectric constant value (ɛr) decreased slightly from 33.4 to 32.2, and τf value increased from −30.3 to −31.9ppm/°C. Dielectric loss of the Nd(Zn0.5Ti0.5)O3 ceramics could be decreased by the small amount of Co substitution. Excellent microwave dielectric properties of ɛr=32.6, Q×f=185,300GHz and τf=−31.3ppm/°C were obtained for the Nd[(Zn0.925Co0.075)0.5Ti0.5]O3 (x=0.075) ceramics sintered at 1390°C for 4h.

Properties of Co Substituted Bismuth Ferrite System by Rapid Liquid Phase Sintering

The multiferroic ceramic samples of Co substituted Bi0.9Nd0.1Fe1-xCoxO3 ( x = 0.00, 0.03, 0.05, 0.07, 0.09, 0.10, 0.20 and 0.30) were prepared by a rapid liquid phase sintering technique. As Co content increases, the Bi0.9Nd0.1Fe1-xCoxO3 samples have a structural transformation from rhombohedral (space group R3c) to cubic structure (space group I23). A small amount of Co substitution maintains the ferroelectric properties while high doping content deteriorates the ferroelectric behavior due to the attendant high leakage current caused by the valence fluctuation of Co ions. It is found that the remnant magnetization (Mr) is enhanced greatly from a value of 4.87  10-6 emu/g at x = 0.00 to 0.054 emu/g at x = 0.30.

Ni-Zn-Co ferrite films prepared at 90°C having μ"=30 at 3 GHz

Ni-Zn-Co ferrite films (Ni/sub 0.16-0.21/Zn/sub 0.30-0.36/Co/sub x/ Fe/sub 2.38-2.46/O/sub 4/, x=0/spl sim/0.16) were deposited by spin-spray ferrite plating method at low temperature of 90/spl deg/C. All the films had a saturation magnetization M/sub s/ larger than 440 emu/cc. A small amount of Co substitution x into Ni-Zn ferrite films changed the magnetic anisotropy in film plane from isotropic to anisotropic and the magnetic easy axis was parallel to the flowing direction of the sprayed solutions on the rotating substrate. The coercivity H/sub c/ and anisotropy field H/sub k/ took small values of 10 and 25 Oe at x=0.03. The complex permeability was measured in the range 20 MHz-3 GHz and very high static permeability /spl mu/' of 120 and resonance frequency f/sub r/ of 900 MHz were achieved at x=0.03. Exhibiting large /spl mu/">30 even at 3 GHz, this Ni-Zn-Co ferrite film is applicable for wave absorbers to suppress the electro-magnetic interference among devices up to microwave frequencies.

Co doping effects on the magnetic and magnetoresistance in Sm 0.35Nd 0.35Pb 0.30Mn 1− xCo xO 3 ( x=0, 0.1, 0.2)

Polycrystalline samples of the Sm 0.35Nd 0.35Pb 0.35Mn 1− x Co x O 3 ( x=0, 0.1, 0.2) at low magnetic fields has been studied by AC susceptibility, and field cooled and zero field cooled magnetisation measurements. We conclude that a small amount of Co substitution tends to destroy the double exchange and broadens the coexistence region of the cluster-glass and ferromagnetic states. Also, the Co doping suppresses the large negative magnetoresistance and it becomes small for x=0.2.

The Effect of Co Substitution for Ni on the Structure and Electrochemical Behavior of T2 and O2 Structure Li2 / 3 [ CoxNi1 / 3 − xMn2 / 3 ] O 2

The effect of Co substitution for Ni on the structure and the electrochemical behavior of has been investigated. It is found that Co can substitute for Ni to form the solid solution which adopts the P2 structure. When prepared by ion-exchanging the Na in for Li, adopts the T2 structure. However, when exists in an O2 structure with stacking faults. This occurs because the Co additions gradually suppress the superlattice ordering of the transition metals in the transition metal layers, which destabilizes the T2 structure. The electrochemical data indicate that a small amount of Co substitution allows the removal of more lithium from the lattice during the first charge process and improves the rate capability of the material. However, preliminary results indicate that the capacity retention with cycle number becomes worse as Co is added. As x in increases, the deintercalation potential moves toward increasingly higher voltage. © 2001 The Electrochemical Society. All rights reserved.

Substitution effect on the unstable ferromagnet CeFe 2

We studied the hybridization effect on the unstable ferromagnet CeFe 2 due to chemical pressure. The small amount of Co substitution for Fe induces a stable AF order at low temperatures. In the AF state, the substituted CeFe 2 shows a giant magnetoresistance at the metamagnetic transition, which originates from the collapse of superzone gap in the antiferromagnetic state. On the other hand, ferromagnetism is stabilized in (Ce 1− x Sc x )Fe 2, even though the lattice parameter decreases. This indicates that ferromagnetism is stabilized by the suppression of antiferromagnetic fluctuation coming from the reduction of 3d–4f hybridizations due to the decrease in the Ce content.

Microstructure and magnetic properties of melt-spun Sm 2Fe 15− xCo xCr 2C 2 ( x=0–4) nanocomposite magnets

The amorphous formation ability, crystallization behavior, microstructure and magnetic properties of melt-spun and heat treated Sm 2Fe 15Cr 2C 2 magnets have been systematically studied using XRD, DSC, TEM and magnetic measurements. It has been found that the as-spun ribbons are comprised of a mixture of α-Fe, a small amount of 2 : 17 phase and an amorphous phase when the wheel speed is 17 m/s and become pure amorphous when the wheel speed is increased up to 61 m/s. The coercivity is dramatically increased by subsequent annealing. A higher annealing temperature combined with a shorter annealing time leads to a higher coercivity and annealing at 900°C for 1 min was found to give the highest coercivity of 12.1 kOe. XRD and TEM studies reveal that the microstructure of the annealed ribbon is composed of 2 : 17 carbide as the majority phase and a small amount of α-Fe as the minority phase. The average grain size at the optimum annealing was found to be about 35 nm for the 2 : 17 and 60 nm for α-Fe. It is further found that a small amount of Co substitution for Fe not only increases the Curie temperature of the 2 : 17 carbides, but also significantly reduces the grain size of α-Fe to about 20 nm, leading to a much smoother hysteresis loop and a better temperature dependence of coercivity.

Electrical transport, magnetism, and magnetoresistance in ferromagnetic oxides with mixed exchange interactions: A study of theLa0.7Ca0.3Mn1−xCoxO3system

In this paper we report the results of an extensive investigation of the La${}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{3}$ system. Substitution of Mn by Co dilutes the double-exchange (DE) mechanism and changes the long range ferromagnetic order of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ to a cluster glass-type ferromagnetic (FM) order similar to that observed in ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{CoO}}_{3}$. This happens even for the lowest Co substitution of $x=0.05$ and persists over the entire composition range studied (0.05$&lt;~x&lt;~$0.5). The Co substitution also destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Co substitution. The charge localization due to Co substitution is likely to have its origin in polaronic lattice distortion. The Co substitution also suppresses the colossal magnetoresistance (CMR) of the pure manganate $(x=0)$ over the entire temperature and composition range and it becomes very small for $x&gt;~0.2$. We conclude that the DE interaction and the resulting metallic state is very ``fragile'' and hence even a small amount of Co substitution can destroy the FM order, the metallic state, and the CMR.