Random Distribution Of Mn Research Articles

Role of Co Content on the Electrode Properties of P3-Type K0.5Mn1-xCoxO2 Potassium Insertion Materials.

Potassium-ion batteries are widely being pursued as potential candidates for stationary (grid) storage, where energy dense K+ insertion cathodes are central to economic and energy efficient operation. To develop robust K-based cathodes, it is key to correlate their underlying electronic states to the final electrochemical performance. Here, we report the synthesis and structure-electrochemical property correlation in P3-type K0.5Mn1-xCoxO2 binary layered oxide cathodes. Spectroscopic analyses revealed a random distribution of Mn and Co in transition metal layers in the oxygen anion framework. In this solid-solution family, Co substitution improved the electronic conductivity and structural stability of P3 phases by minimizing local lattice distortion. Co substitution led to a systematic shift of the Co4+/Co3+ and Mn4+/Mn3+ redox potentials. Galvanostatic cycling showed that the Co substitution reduced the initial capacity while improving the cycling stability. The role of Co on final electrochemical properties of P3-layered oxides has been elucidated as a design tool to develop practical potassium-ion batteries.

55Mn NMR study of quaternary half-metallic ferromagnetic Co2Mn1−xFexSi Heusler compounds

In this work, the ${}^{55}$Mn spin-echo nuclear magnetic resonance technique is used to systematically analyze the complete substitutional series Co${}_{2}$Mn${}_{1\ensuremath{-}x}$Fe${}_{x}$Si in terms of the resonance frequencies of the satellite structure and the corresponding hyperfine fields of the ${}^{55}$Mn nuclei. The frequency spacing between satellite lines is constant within a compound, but decreases with increasing Fe concentration $x$, which originates in changes in the band structure. These changes are also responsible for the altered resonance frequencies observed for the same third shell environment but corresponding to a different overall Fe concentration $x$. All modifications in the hyperfine field upon substitution of Mn by Fe can be uniquely assigned to an entirely random distribution of Mn and Fe limited to only one (4$b$) out of four fcc sublattices constituting the $L{2}_{1}$ Heusler structure, demonstrating that the complete substitutional series Co${}_{2}$Mn${}_{1\ensuremath{-}x}$Fe${}_{x}$Si is crystallographically very well defined. This very high degree of order sets the stage for the observation of stable half-metallic ferromagnetism which is typically very sensitive to the structural order.

Crystal and magnetic structure of the Bi2RuMnO7 pyrochlore: A potential new cathode for solid oxide fuel cells

A new pyrochlore-like phase of composition Bi2RuMnO7 has been prepared as polycrystalline powder, structurally characterized from X-ray diffraction (XRD) and neutron powder diffraction (NPD) data, in complement with magnetic and transport measurements, and finally tested as cathode material for solid-oxide fuel cells (SOFCs). Bi2RuMnO7 pyrochlore is defined in a cubic unit cell with space group Fd-3m; the structural analysis from NPD data unveils a singular feature consisting of a cation disorder of Mn and Bi atoms between A and B positions. This disorder leads to the reduction of Mn4+ at B position to Mn2+ at A position and the oxidation of Bi3+ at A position to Bi5+ at B position. The low-temperature NPD data indicates an antiferromagnetic coupling of two subsets of Mn4+/Ru4+ spins, demonstrating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites. The obtained compound displays a metallic-like behavior with conductivity values at the SOFCs working temperatures (650–850 °C) that span between 39 and 28 Scm−1. Bi2RuMnO7 shows good performance working as a cathode with LSGM electrolyte, yielding output power densities of 360 mW cm−2 at 850 °C with pure H2 as a fuel.

Low-dilution limit of Zn1−xMnxGeAs2: Electrical and magnetic properties

We present the studies of electrical transport and magnetic interactions in Zn1−xMnxGeAs2 crystals with low Mn content 0≤x≤0.042. We show that the ionic-acceptor defects are mainly responsible for the strong p-type conductivity of our samples. We found that the negative magnetoresistance with maximum values of about −50% is related to the weak localization phenomena. The magnetic properties of Zn1−xMnxGeAs2 samples show that the random Mn-distribution in the cation sites of the host lattice occurs only for the sample with the lowest Mn-content, x = 0.003. The samples with higher Mn-content show a high level of magnetic frustration. Nonzero Curie-Weiss temperature observed in all our samples indicates that weak ferromagnetic (for x = 0.003) or antiferromagnetic (for x>0.005) interactions with the Curie-Weiss temperature, |Θ|<3 K, are present in this system. The Ruderman-Kittel-Kasuya-Yosida model, used to estimate the Mn-hole exchange integral Jpd for the diluted Zn0.997Mn0.003GeAs2 sample, makes possible to estimate the value of Jpd=(0.75 ± 0.09) eV.

The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction

High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120 K with a (121212) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites.

Ga1−xMnxN epitaxial films with high magnetization

We report on the fabrication of pseudomorphic wurtzite Ga1−xMnxN grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering, the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, and no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm3.

Evolution of the crystal and magnetic structure of the R2MnRuO7 (R = Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) family of pyrochlore oxides

The members of the family of pyrochlore oxides with the formula R(2)MnRuO(7) (R = Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) have been synthesized and characterized. Polycrystalline samples were prepared by a soft chemistry procedure involving citrates of the different metal ions, followed by thermal treatments in air or O(2) pressure. The crystallographic and magnetic structures have been analysed from X-ray diffraction (XRD) and neutron powder diffraction (NPD) data, in complement with magnetic measurements; the evolution along the series of the crystallographic parameters (unit-cell parameters, bond distances and angles) is discussed. In R(2)MnRuO(7) pyrochlores, Mn and Ru ions statistically occupy the 16c sites in a cubic unit cell with space group Fd ̅3m, which defines an intrinsic frustrated three-dimensional system. In all the cases, the low-temperature NPD data unveils an antiferromagnetic coupling of two subsets of Mn(4+)/Ru(4+) spins, indicating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites. At lower temperatures there is a polarization of the R(3+) magnetic moments, which also participate in the magnetic structure, when a magnetic rare earth is present.

The Ho2MnRuO7 pyrochlore oxide: Magnetic structure versus magnetic frustration

A pyrochlore-like phase of composition Ho2MnRuO7 has been synthesized by a soft-chemistry procedure followed by thermal treatments at moderate temperatures up to 900 °C for 12 h in air. It has been characterized by x-ray diffraction and neutron powder diffraction (NPD), as well as dc and ac susceptibilities. As in the parent Ho2Mn2O7 oxide, the magnetic Mn and Ru ions statistically occupy the 16c sites in a cubic unit cell with space group Fd3¯m, which define a potentially frustrated three-dimensional array of corner sharing (Mn,Ru)4 tetrahedra. The dc and ac magnetic susceptibilities of Ho2MnRuO7 display a sharp increase near 60 K. In addition, the field-cooled and zero-field-cooled curves diverge below 30 K. The ac data present frequency variability below 60 K and broad frequency dependent maxima at lower temperatures (∼30 K), suggesting a spin-glass like behavior similar to Ho2Mn2O7. However, a low-temperature NPD study of the magnetic structure unveils an antiferromagnetic coupling of two subsets of Mn4+/Ru4+ spins, indicating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites; at lower temperatures there is a polarization of the Ho3+ magnetic moments, which also participate in the magnetic structure. Under an external magnetic field the Ho moments become totally polarized, giving a saturation magnetization at 2 K of 10.8 μB/f.u. at 5 T.

Ferromagnetism analysis of Mn-doped CuO thin films

Mn (6.6–29.8%)-doped CuO thin film fabricated on a thermally oxidized silicon substrateby radio-frequency magnetron sputtering has been reported. The films were structurallycharacterized using x-ray diffraction with Rietveld refinement. The analysis indicates that Mnuniformly substituted at the Cu position in the CuO lattice. 5% cation vacancies were detectedat the Cu sites and are supposed to be responsible for the p-type electrical conduction ofCu1−xMnxO films. No evidence for large scale Mn aggregation was found in the composition rangeanalyzed. The origin of ferromagnetism was analyzed in the context of competition amongseveral interactions among Mn and Cu ions. A chain model was developed to simulate theferromagnetic behavior with the random Mn distribution in the samples. The consistencybetween simulation and experiment strongly indicates that the ferromagnetism mainlyarises from the super-exchange interactions of Mn–O–Cu–O–Mn coupling in the [] chain and Mn–O–Mn coupling contributes to the antiferromagnetism.

Influence of antiferromagnetic exchange interaction on magnetic properties of ZnMnO thin films grown pseudomorphically on ZnO (0001¯) single-crystal substrates

This study investigated the influence of antiferromagnetic exchange interaction on magnetic properties of ZnMnO thin films grown on ZnO (0001¯) single-crystal substrates. Using pulsed laser deposition, ZnMnO films with Mn concentrations as high as 14.1at.% were prepared. Investigations revealed that the lattice constant along the c axis of the ZnMnO films increases linearly with increasing Mn concentration. The lattice constant along the a axis is independent of the Mn concentration and is equal to that of the ZnO substrate, suggesting pseudomorphic growth of ZnMnO films. An atomic force microscopy image of the ZnMnO film grown at 640°C shows a step-and-terrace structure. An interference fringe around the ZnMnO 0004 symmetric diffraction image is clearly visible in the 2θ-ω x-ray diffraction profile, suggesting that the samples have a smooth surface and an abrupt interface. The intrinsic magnetic properties of these pseudomorphically grown ZnMnO films with smooth surfaces were evaluated. At temperatures greater than 1.85K, ZnMnO films with Mn concentration up to 14.1at.% exhibit typical paramagnetic characteristics. As calculated using the probabilities for a random Mn distribution, the theoretically magnetic moment agreed with the experimentally determined saturated magnetic moment, indicating an antiferromagnetic exchange interaction between the nearest-neighbor Mn ions.

Effects of random distribution of Mn,Fe in Co2Mn1−xFexSi Heusler compounds probed by Mn55 nuclear magnetic resonance

Recent spin echo nuclear magnetic resonance (NMR) revealed that the half-metallic Co2Mn1−xFexSi Heusler alloys exhibit the L21 structure with random distribution of Mn and Fe on the 4b Wyckoff position. This random distribution is most prominent in the third coordination shell of the Mn55 nuclei, as this shell is the first magnetically active shell, leading to a line splitting in the Mn55 NMR spectra. A comparison, as presented in this paper, of all Mn55 NMR satellite lines shows that the resonance frequencies corresponding to the same number of Fe atoms in the third shell of Mn55 shift to slightly different resonance frequencies with increasing overall Fe content x. This shift is related to the constructive contribution of higher shells to the hyperfine field. These higher shells affect also the satellite linewidth, leading to a parabolic behavior with increasing Fe concentration x. This parabolic behavior is modified by the frequency spacing related to the replacement of Mn by Fe.

Probing the random distribution of half-metallic Co2Mn1−xFexSi Heusler alloys

Co 2 Mn 1 − x Fe x Si Heusler alloys crystallize in the L21 structure. This structure type requires random distribution of Mn and Fe in case of the mixed alloys. The spin echo nuclear magnetic resonance (NMR) technique probes the direct local environments of the active atoms and is thus able to resolve next neighboring shells providing a unique tool to verify the random distribution of Mn and Fe in Co2Mn1−xFexSi. Exemplarily, the half-metallic quaternary Heusler alloy Co2Mn0.5Fe0.5Si was investigated by means of NMR. The Mn55 NMR measurements unambiguously demonstrate the random distribution of Mn and Fe on the 4b Wyckoff position in Co2Mn0.5Fe0.5Si.

R 3Mn 1.5CuV 0.5O 9 (R = Y, Ho, Er, Tm, Yb and Lu) and Lu 3Mn 3−3 xCu 2 xV xO 9: New noncentrosymmetric oxides related to YMnO 3

We report formation of new noncentrosymmetric oxides of the formula, R 3Mn 1.5CuV 0.5O 9 for R = Y, Ho, Er, Tm, Yb and Lu, possessing the hexagonal RMnO 3 (space group P6 3 cm) structure. These oxides could be regarded as the x = 0.5 members of a general series R 3Mn 3−3 x Cu 2 x V x O 9. Investigation of the Lu–Mn–Cu–V–O system reveals the existence of isostructural solid solution series, Lu 3Mn 3−3 x Cu 2 x V x O 9 for 0 < x ≤ 0.75. Magnetic and dielectric properties of the oxides are consistent with a random distribution of Mn 3+, Cu 2+ and V 5+ atoms that preserve the noncentrosymmetric RMnO 3 structure.

A multiscale study of ferromagnetism in clustered (Ga,Mn)N

Magnetic interactions in (Ga,Mn)N are studied on the microscopic inter-cluster andintra-cluster scales using first-principles calculations. Ferromagnetic transitiontemperatures are calculated using Monte Carlo methods. Randomness in Mnsubstitution is found to reduce Curie temperatures by about 10–20% from thoseof the corresponding regular (Ga,Mn)N lattice due to clustering. Nevertheless,high Curie temperatures reaching above room temperature are obtained even forcompletely random Mn distribution in (Ga,Mn)N for the Mn concentration ofx≥13.5%. Increasing clustering is always found to decrease the Curie temperature—especially whentetramer clusters are formed.

CMR in a manganite with 50% of Ti in the Mn sites

SrLaMnTiO 6 orthorhombic perovskite has been synthesized by the liquid-mix technique. Structural characterization from X-ray and neutron diffraction shows a random distribution of Mn and Ti atoms. This material shows ferromagnetic ordering with a Tc = 380 K which can be interpreted in terms of a FM mode along y-axis. A M–I transition and a negative MR response of 90% have been detected at 210 K. AC and DC (ZFC and FC) magnetization measurements show an anomaly at low temperatures which has been attributed to effects of pinning of the FM domain walls rather than SG behaviour. Besides this, linear relation between coercitive field and T 1 / 2 is interpreted considering the existence of magnetic clusters of the same size embedded in a paramagnetic matrix. Finally the magnetocaloric properties of the title material have been studied and a discrete value of Δ S max = 0.19 J kg −1 K −1 at RT has been found.

Magnetization steps in the diluted Heisenberg layer materials(CH3NH3)2MnxCd1−xCl4: Equilibrium data at 0.6 K

The magnetization $M$ of ${({\mathrm{C}\mathrm{H}}_{3}{\mathrm{N}\mathrm{H}}_{3})}_{2}{\mathrm{Mn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Cl}}_{4}$, with $x$ from 0.025 up to 0.265, was measured at 0.6 K in a slowly varying magnetic field $B$ up to 17 T. The exchange interaction in these strongly diluted planar magnetic materials is antiferromagnetic. The in-plane cation structure is well approximated by a square lattice. The observed qualitative features, listed in the order that they appear in increasing $B$, are as follows: a fast rise of $M$, starting at $B=0$; a magnetization plateau (plateau of ``apparent saturation''); a large magnetization step (MST), attributed to nearest-neighbor (NN) pairs; a second magnetization plateau; another large MST from NN pairs; and a third plateau that is not completed below the highest available $B$. These features are expected from the NN cluster model presented in the preceding paper. The magnetic fields at the two MST's give ${J}_{1}∕{k}_{\mathrm{B}}=(\ensuremath{-}4.39\ifmmode\pm\else\textpm\fi{}0.10)\phantom{\rule{0.3p}{0ex}}\mathrm{K}$ for the NN exchange constant. This value is slightly lower than reported for the undiluted $(x=1)$ member of this series, ${({\mathrm{C}\mathrm{H}}_{3}{\mathrm{N}\mathrm{H}}_{3})}_{2}\mathrm{Mn}{\mathrm{Cl}}_{4}$. A smaller ${J}_{1}$ when $x\ensuremath{\leqslant}0.265$ may be the result of an in-plane expansion with decreasing $x$, caused by the slightly larger ${\mathrm{Cd}}^{2+}$ ion compared to ${\mathrm{Mn}}^{2+}$. Analysis of the initial rise of $M$ at low $B$ indicates the presence of weak interactions that are not included in the NN cluster model. This conclusion is consistent with the observation (to be reported later) of a weak exchange interaction with a neighbor that is more distant than a NN. The apparent saturation value ${M}_{s}$, at the first magnetization plateau, was determined for all seven samples. There is a fair agreement with the values expected from a random distribution of the Mn ions over all cation sites. The largest deviation is for samples with $x\ensuremath{\geqslant}0.15$, where the measured ${M}_{s}$ is somewhat higher. In the same samples the magnetization jump $\ensuremath{\Delta}M$ at the MST's from NN pairs is somewhat smaller than for a random Mn distribution. A proposed explanation of the discrepancies for $x\ensuremath{\geqslant}0.15$ postulates that the probability that a cation site is occupied by a ${\mathrm{Mn}}^{2+}$ is lowered by the presence of other ${\mathrm{Mn}}^{2+}$ ions at one or more NN cation sites.

The crystal structure of CaLaMnFeO6 double perovskite

A single-phase, polycrystalline sample of the double perovskite CaLaMnFeO6 was prepared by solid-state synthesis and characterized with neutron powder diffraction. The compound belongs to the class of AA′BB′O6 perovskites with a random distribution of Mn and Fe atoms over the B-cation sub-lattice. Rietveld refinement of the room temperature neutron powder diffraction data revealed that the crystal structure of CaLaMnFeO6 is disordered with orthorhombic symmetry (space group Pbnm) having lattice parameters a=5.4468(5) Å, b=5.4386(5) Å, c=7.6862(5) Å. The crystal structure is distorted due to the small size of the La+3 and Ca+2 cations, which force the (Mn/Fe)O6 octahedra to tilt in order to optimize the 12-coordinated (La/Ca)–O bond distances.

Investigation of possible superstructure and cation disorder in the lithium battery cathode material LiMn 1/3Ni 1/3Co 1/3O 2 using neutron and anomalous dispersion powder diffraction

A study has been conducted to discover whether the recently reported high-capacity lithium battery material LiMn 1/3Ni 1/3Co 1/3O 2 possesses a superstructure due to ordering of the transition metal cations. A recent paper in the literature concluded from ab initio calculations that, if a superstructure exists, it would likely take the form of a [√3×√3]R30° type superlattice rather than an ordered stacking of Co–O 2, Ni–O 2, and Mn–O 2 slabs. A suitable technique to detect the presence or otherwise of a superstructure in this material is neutron diffraction due to the contrast between Mn, Ni, and Co neutron scattering lengths. An alternative method to enhance the contrast between elements close in the periodic table is to use resonant diffraction techniques. The beneficial contrasts afforded by each method may be retained by conducting a simultaneous refinement using both neutron and X-ray data. It was found that LiMn 1/3Ni 1/3Co 1/3O 2 did not appear to possess either of the proposed types of supercell and that the data were consistent with a random distribution of Mn, Ni, and Co over the R-3m 3a sites. Simultaneous Rietveld analysis showed that some nickel displaced lithium from the 3b site, whilst the manganese and cobalt remained solely on the transition metal 3a site.

Magnetization steps inMn0.084Zn0.916F2:Exchange constant and Mn distribution

The magnetization M of ${\mathrm{Mn}}_{0.084}{\mathrm{Zn}}_{0.916}{\mathrm{F}}_{2}$ was measured at 20 mK in magnetic fields H up to 115 kOe and at 0.65 K in fields up to 175 kOe. The magnetization was independent of magnetic field direction and showed no hysteresis. After a fast rise of M at low H, several magnetization steps (MS's) were observed. These MS's arose from ${\mathrm{Mn}}^{2+}$ pairs and triplets in which the spins are coupled by the dominant antiferromagnetic exchange constant, ${J}_{2}$ between next-nearest neighbors. The magnetic fields at the steps gave ${J}_{2}=\ensuremath{-}1.94\ifmmode\pm\else\textpm\fi{}0.01 \mathrm{K}$ in this diluted magnetic material. The observed magnetization curves are in very good agreement with computer simulations which assume a random Mn distribution. However, at 20 mK the widths of MS's are much larger than expected from thermal broadening alone. Possible mechanisms for nonthermal broadening are discussed. Theoretical results for cluster statistics, for ${J}_{2}$ clusters up to quintets, and for the fields at the MS's from the various quintet types are presented. These theoretical results also apply to nearest-neighbor ${(J}_{1})$ clusters in a body-centered-cubic cation lattice.

Direct and indirect preparation of layered quaternary manganese tellurides; AMn xM yTe 2 (A=Li, Na; M=Cu, Ag; x+ y≤2)

A series of layered quaternary tellurides with AMn x M y Te 2 (A=Li, Na; M=Cu, Ag; x+ y≤2) compositions were prepared in two different ways; direct synthesis from elemental starting materials and reaction of coinage metals (Cu or Ag) with ternary tellurides, AMnTe 2 (A=Li, Na) with partially empty tetrahedral sites. Products were characterized by single crystal and powder X-ray diffraction, atomic absorption (AA) measurements, and wavelength dispersive spectrometry (WDS). These compounds adopt the CaAl 2Si 2 structure type (space group Pm 3 1 , No. 164), in which Te atoms are arrayed by hexagonal closed packing with random distribution of Mn and M (Cu or Ag) atoms in the tetrahedral sites. Alkali metals reside in octahedral sites between two layers to complete the structure. Resistivity measurements showed that these compounds are either insulators or semiconductors.