Mn In Cu Research Articles

Paramagnetism found in Mn-doped CuO nanofibers at room temperature explained by XPS , XAS and Rietveld method

CuO and 3 % Mn-doped CuO nanofibers were synthesized employing the electrospinning method. X-ray diffraction (XRD) verified a monoclinic phase with a C 2/c space group. An electronic density analysis, obtained using Fullprof software, was projected on the (110) and (001) planes for both materials, showing modifications in the Cu positions. This fact generated vacancies involved in the paramagnetism formation in the Mn-doped CuO nanofibers, in contrast to the mixed magnetic phase composed by both ferromagnetic and paramagnetic behaviors found in the undoped CuO. The vacancy amount was quantified by X-ray absorption spectroscopy (XAS) applying CASTEP software. In addition, an analysis from Cu 2p XPS peaks supports the predicted Cu-Cu rearrangement by the Fullprof software study, while the presence of Cu1+ confirms the substitution of Mn for Cu in the doped sample.

Direct synthesis of methyl formate from syngas on Cu–Mn mixed oxide catalyst

Cu–Mn mixed oxides with different Cu/Mn molar ratios were prepared by ammonia complexation method, and their catalytic performances have been evaluated for the direct synthesis of methyl formate (MF) from syngas. The catalysts were characterized by N2 adsorption-desorption isotherm, XRD, TEM, SEM, FT-IR, XPS and TPR measurements. Results revel that incomplete spinel of Cu1.5Mn1.5O4, CuO and amorphous Mn species are formed in all Cu–Mn catalysts. The interaction between Cu and Mn in Cu–Mn catalyst delays the reduction of samples compared with pure Cu oxide. For the direct synthesis of MF from syngas, Cu–Mn catalysts showed higher catalytic activities and MF selectivities than pure Cu or Mn oxides. CO conversion increases and MF selectivity decreases with the rise of Cu/Mn ratios in catalysts, which could be attributed to the phase compositions, specific surface areas, and the reducibility of the catalysts.

Defects and thermoelectric performance of ternary chalcopyrite CuInTe2-based semiconductors doped with Mn

In thermoelectric (TE) semiconductors, there are three physical parameters that govern the TE performance (i.e. Seebeck coefficient (), electrical conductivity (), and thermal conductivity ()); they are interrelated, hence it is hard to optimize them simultaneously. In order to improve the TE performance, we need to further explore new materials. Ternary chalcopyrite (diamond-like) I-III-VI2 semiconductors (Eg = 1:02 eV) are new materials of the TE family, which have potential in conversion between heat and electricity. Since in the ternary chalcopyrite structure, such as Cu(Ag) MTe2, there is an inherent Coulomb attraction between charged defects MCu(Ag)2+ and 2VCu(Ag)- (a native defect pair, i.e., metal M-on-Cu or Ag antisites and two Cu or Ag vacancies), hence the electronic and structural properties can easily be tailored if these two defects, along with the creation of other defects, are modified through the introduciton of foreign elements. Besides, the ternary I-III-VI2 compounds often show tetragonal distortion because 0.25, = c/2a 1 (here and are the anion position displacement parameters, and a and c are the lattice parameters), and the cationanion distances are not equal (dCuTedInTe). Any occupation by foreign elements in the cation sites of I-III-VI2 will cause the redistribution of bond charges between I-VI and III-VI, thus leading to a tiny adjustment of the crystal structure and altering the phonon scattering behavior. In this work, we substitute Mn for Cu in the chalcopyrite CuInTe2 and prepare the Cu-poor Cu1-xInMnxTe2 semiconductors. Investigations of Z-ray patterns after Rietveld refinement reveal that Mn prefers In to Cu lattice sites for low Mn content (x 0.1), thus creating MnIn- as an active acceptor, and improving the carrier concentration (n) and electrical conductivity as Mn content increases. However, Mn can either occupy In or Cu sites simultaneously when x 0.1, and generate both the donor defect MnCu+ and the acceptor defect MnIn-. In this case, annihilation may occur between these two defects, allowing the reduction in both the defect and carrier concentrations. Because of the annihilation between the two defects, two values (|| = |-0.25| and ||= |-1.0|) reduce, this only yields a subtle change in the difference between mean cation-anion distance (RInTe-RCuTe), indicating a small distortion tendency in lattice structure as Mn content increases. Because of this, there is a limited enhancement in lattice thermal conductivity (L) at high temperatures. As a consequence, we attain an optimal TE performance at a certain Mn content (x = 0.05) with the dimensionless figure of merit (ZT) ZT = 0.84 at 810.0 K, which is about twice as much as that of Mn-free CuInTe2.

Phenomenological analysis of the s-d exchange interaction in dilute Cu-Mn alloy at helium temperature

The S-d exchange interactions in dilute Cu-Mn alloys was studied on concentration (C) varying between 10.5 and 2081.8 ppm of Mn in Cu within the (0.03K–4.2K) temperature range. Using electrical resistivity data on those alloys, the s-d exchange integral (Jsd), which is negative, has calculated to show a clear dependence on (Ln C). This dependence, confirming thus the dominance of Kondo effect below 1000 ppm impurity concentration, but above this concentration, we expected an interference between Kondo effect and spin glass regime, which mean that spin glass regime has to prevail more than Kondo effect.

The study of structure, magnetism, electricity, and their correlations at martensitic transition for magnetostriction system Cu1−xMnxNMn3 (0 ≤ x ≤ 0.5)

The antiperovskite functional compound CuNMn3 exhibits magnetostriction below the non-collinear ferromagnetic (FM)-paramagnetic (PM) transition (accompanied by a martensitic transformation). After the substitution of Mn for Cu, martensitic transformation is decoupled from FM transition. Meanwhile, the tetragonality of the martensitic phase and the magnetostriction are weakened. The combined analysis indicates that the spin, charge, and lattice are closely coupled around martensitic transformation temperature (TMS). The low-temperature martensitic phase is associated with a metastable magnetic state characterized by small magnetocrystalline anisotropy. Additionally, the depression of TMS with introducing the Mn dopant is revelatory for the development of low-temperature negative thermal expansion material.

Local lattice instability and superconductivity inLa1.85Sr0.15Cu1−xMxO4(M=Mn, Ni, and Co)

Local lattice structures of La$_{1.85}$Sr$_{0.15}$Cu$_{1-x}$M$_x$O$_4$ (M=Mn, Ni, and Co) single crystals are investigated by polarized extended x-ray absorption fine structure (EXAFS). The local lattice instability at low temperature is described by in-plane Cu-O bond splitting. We find that substitution of Mn for Cu causes little perturbation of local lattice instability while Ni and Co substitution strongly suppresses the instability. The suppression of superconductivity by Cu-site substitution is related to the perturbation of lattice instability, indicating that local lattice instability (polaron) plays an important role in superconductivity.

The roles of Cu, Zn and Mn in Cu 0.5Zn 0.5Mn 2O 4 spinel-lattice catalyst for methanol decomposition

Cu 0.5Zn 0.5Mn 2O 4 spinel-lattice catalyst has been studied for methanol decomposition by in situ infrared (IR) spectroscopy analysis and micro reactor study. Methoxy species is formed by dissociative adsorption of methanol which subsequently converts into formate species via step-wise dehydrogenation process. The activities of surface intermediates on reduced CuO, ZnO and Mn 2O 3 catalysts are strongly affected by the ease of hydrogen desorption from the site, the strength of C–H bonding and the availability of oxygen. A synergism between Cu and MnO whereby the Cu serves as a sink for reverse hydrogen atoms spillover from MnO has been proposed. The micro reactor analysis correlates well with the IR results.

Unusual impurity effects on the dielectric properties of CaCu 3− xMn xTi 4O 12

CaCu 3Ti 4O 12 has a large dielectric constant (ε∼10 4 at 300 K) , which is almost constant above 100 K , followed by a 100-fold reduction below 100 K . The physical mechanism of this anomalous behavior has been extensively investigated. We found that only 2% substitution of Mn for Cu dramatically quenches the huge ε of 10 4 down to 100 over the measured temperature range from 4.2 to 300 K . In usual substitution effects, 2% impurity induces a tiny change in ε of the order of 2%. Thus the present substitution effect suggests that dipole moments cause fluctuating ferroelectric domains in CaCu 3Ti 4O 12, as is similar to the frustrated dipole glass in LuFe 2O 4.

Lattice-distortion effects on the magnetism of Mn impurities in Al and Cu

Self-consistent calculations with the discrete variational method in the framework of local spin-density theory were performed for 43-atom embedded clusters representing a Mn impurity in Al and Cu hosts. Effects of local lattice relaxation were explored by varying the distance between Mn and the nearest-neighbor host atoms. It was found that the magnetic moment of Mn in Al is much more sensitive to local lattice distortion than Mn in Cu. At the equilibrium Mn nearest-neighbors distance, as determined by x-ray absorption fine-structure measurements, a reduction of 34% of \ensuremath{\mu} in Al is obtained, relative to the host lattice distance. Mechanisms related to the effect of the environment on \ensuremath{\mu} are discussed. The Mn 3s exchange splitting observed in x-ray photoelectron spectra is also investigated, and it is found that it may not be taken as evidence of a 3d moment in the ground state.

Substitution of Mn for Cu in the high T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7- delta /

Samples of YBa/sub 2/(Cu/sub 1-x/Mn/sub x/)/sub 3/O/sub 7- delta /, with x=0.0, 0.025, 0.05, 0.075, 0.10, 0.15, and 0.20, were prepared by the solid diffusion method. Superconductivity with T/sub c/ in the range of 84-92 K was observed through electrical resistivity and magnetic susceptibility measurements. The substitution of Mn for Cu practically did not affect the onset temperature in the resistive transition, although a strong correlation between the transition width broadening and the increase of Mn content was observed. This fact is consistent with the reduction of the superconducting volume fraction determined through the normalized susceptibility data. X-ray diffraction revealed the occurrence of additional phases increasing with the Mn concentration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmission electron microscopy study of the stacking-fault energy and dislocation structure in CuMn alloys

Abstract Single crystals of copper-based manganese alloys (Cu−1.05, 1.3, 3.3, 5.05 and 11.6 at.%Mn) were grown and deformed in tension at room temperature. The weakbeam method of electron microscopy has been used to resolve the partial dislocations and to determine the stacking-fault energy γ. Contrary to most other Cu alloys, the value of γ does not decrease with increasing solute content. It stays the same for all the investigated CuMn alloys and corresponds to the value of pure Cu (γ = 41 mJm−2). It is difficult to include the results in a γ against e/a plot since the valency value of Mn in Cu cannot be specified. In Cu−11.6 at.%Mn a pronounced planar dislocation structure is observed and it is suggested that this is caused by the occurrence of short-range order. The large values of the critical resolved shear stress of the investigated CuMn alloys cannot arise from chemical locking (the Suzuki effect) since γ does not change with solute concentration.

Nuclear spin-lattice relaxation of dilute Mn in Cu, Ag, and Au

We have developed a new method of determining nuclear spinlattice relaxation times of dilute impurity nuclei in non-magnetic host metals. Direct measurement of these extremely rapid relaxation times has hitherto been difficult. The present method is based on fast pulsed heating of a sample containing oriented radioactive nuclei and is applicable to a wide range of impurity-host combinations and over a large range of applied magnetic fields. Results are presented for extremely dilute Mn in noble metal hosts.

Isotope effect of manganese and simultaneous impurity diffusion of chromium and zinc in copper

AbstractThe isotope effect E = 0.310 as a mean value is measured at T = 1200 K for impurity diffusion of 52Mn/54Mn in copper. The corresponding correlation factor f2 = 0.36 is relatively small in comparison with the published results of Fe, Co, and Ni in Cu. The small value of f2 and the faster diffusivity of Mn with regard to self‐diffusion of Cu can be explained by the strong lattice distortions of Mn in Cu. Valence effects are accordingly less important. The frequency ratios for vacancy jumps and the vacancy flow effect are calculated. The free binding enthalpy of the vacancy—impurity complex is estimated. Simultaneously to Mn, the tracer diffusion of 51Cr and 65Zn is determined. The different evaporation effects of the tracer are taken into account in the evaluation of the diffusion coefficients.

Numerical simulation of spin-glass transition phenomena (invited)

Results are presented from a continuing investigation of spin-glass transition effects by numerical simulation. The model is one of classical unit vectors randomly distributed on an fcc lattice, with RKKY exchange coupling and nearest-neighbor dipolar coupling in an approximate representation of dilute Mn in Cu. Results for system energy and for dipolar energy as a function of temperature show no resolvable features at the freezing temperature TG* in accord with the high-precision specific heat data of Fogle, Boyer, Phillips, and Van Curen. Additional details of shattered susceptibility behavior in the vicinity of the ground-state transition are presented. Further data on freezing temperatures as a function of dipolar coupling strength D show a trend toward macroscopic behavior (i.e., TG* independent of D) with a sample of 4928 spins. Finally, a moderately sharp onset of freezing transverse to an applied magnetic field is found, as predicted by the mean-field calculations of Toulouse and Gabay. As expected, this transition is unrelated to transverse susceptibilities.

New applications of high-temperature solution calorimetry III. Enthalpies of formation of Mn 2B, MnB, and MnB 2

The enthalpies of formation of three manganese borides have been measured by solution calorimetry in liquid copper at 1386 K. The following results are reported: αH f( 1 3 Mn 2B) = − (31.7±2.0)kJ ·mol −1, αH f( 1 2 MnB) = − (35.8±2.4)kJ ·mol −1, and αH f( 1 2 MnB 2) = − (21.1±3.4)kJ ·mol −1. The value for MnB 2 is only a preliminary one. We have also measured: (a) the enthalpies of mixing of { x BB(s) + (1 − x B)Cu(l)} (up to x B ≈ 0.015) at 1381 K, and (b) the enthalpies of solution of Mn(s) in Cu(l) at the same temperature. Comparisons between the enthalpies of solution of {(1 − x Mn)B + x MnMn} in Cu with the corresponding values for Mn in Cu and for B in Cu show evidence of strong chemical interaction between dissolved manganese and boron. This is interpreted to indicate extensive formation of a B a Mn b complex. The stoichiometry of this complex is not known. However, it tends to dissociate at higher a b = (1 − x Mn ) x Mn ratios.

Scaling of Nonlinear Susceptibility in MnCu and GdAl Spin-Glasses

SQUID measurements of susceptibility X versus field 0 are fitted by X= yp —p~H at a given temperature T, for two classic spin-glasses: 4.6' Mn in Cu (polycrystalline) and 37% Gd in Al (amorphous). X&(T) shows a much stronger anomaly than po(T), while a(T) has a minimum at the freezing temperature T~. The data can also be scaled according to y, —X=H' f((T Tf)—/H' ~) with 6= 5+1 and y = 4 5+p 5.

Exchange stiffness of a spin-glass

Numerical estimates are reported for the exchange-stiffness constant ${\ensuremath{\rho}}_{s}$ of a dilute, Ruderman-Kittel-Kasuya-Yosida---coupled spin-glass at zero temperature. Conventional stiffness behavior is found, with no resolved trend in ${\ensuremath{\rho}}_{s}$ over simulation volumes of constant cross section and lengths in the ratio 1:2:3. The value of ${\ensuremath{\rho}}_{s}$ is found to scale as ${c}^{\frac{4}{3}}$ ($c$ being the atomic fraction of magnetic ions), as expected for an ${r}^{\ensuremath{-}3}$ interaction potential and to be \ensuremath{\sim}25 times smaller than the value for a comparable ferromagnet. When one uses the Halperin-Saslow expression for the spin-wave dispersion constant, a parabolic density of spin-wave modes is found which is consistent with the low-frequency ($\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\lesssim}0.2$ meV) density of excitations recently given for 0.9 at.% Mn in Cu from numerical simulation studies.

Anomalous thermal expansion of dilute CuMn and AgMn alloys below 50K

Excess expansion coefficient data on anomalies associated with Mn concentrations up to approximately 7 at.% are reported for both Cu and Ag hosts. For alloys with 0.55 at.%, 1.2 at.% and 2.2 at.% Mn in Cu a temperature-independent magnetic Gruneisen parameter gamma m is found by comparison with specific heat data from 4-25K, yielding gamma m=2.7, 3.1 and 3.2 respectively. For Ag-1.0 at.% Mn a value of 3.7 is tentatively ascribed to gamma m.

Comments on "Host Nuclear Resonance in a Spin-Glass:CuMn"

New data on a higher concentration (\ensuremath{\sim}1%) of Mn in Cu than that studied by MacLaughlin and Alloul exhibit fundamentally different behavior for $T\ensuremath{\ll}{T}_{c}$, where ${T}_{c}\ensuremath{\sim}10$ K is the "spin-glass" transition temperature. In particular, we find evidence for a "frozen" configuration of Mn spins at $T=1.6 \mathrm{and} 4.2$ K, in better accord with the muon-precession studies of Murnick et al.

X-ray K absorption edges of alloys. IV. Mn solid solutions with Cu, Ni, Co, and Fe

The x-ray K absorption spectra of the constituent atoms in fcc solid solutions of Mn in Cu, Ni, Co, and Fe show systematic changes taking place with increasing manganese concentration which it is not possible to explain in terms of the rigid-band model for alloys. A decline in the initial rise in absorption with increasing Mn content is observed for all absorption edges except for Mn in Mn–Fe solid solutions, in which case an increase takes place. A tentative explanation, based on hybridization of the outer states upon alloying, is proposed for Mn–Cu and Mn–Ni alloys.