Mn-rich Side Research Articles

An evaluation of the Mn–Ga system: Phase diagram, crystal structure, magnetism, and thermodynamic properties

The Ni–Mn-Ga alloy system is attractive due to its functional properties with potentials in various applications. However, the fundamental alloy thermodynamics of the binary Mn–Ga system is still lack of investigation. Therefore, a comprehensive evaluation of the Mn–Ga is performed in this work. Different versions of Mn–Ga phase diagrams available in the literature are reviewed. A new version of the Mn–Ga phase diagram is recommended along with possible invariant reactions. The crystal structure, magnetic transition, and thermochemical properties of intermetallic compounds are reviewed by considering available experimental and modeling such as ab initio calculations. In fact, more experimental information on the Mn-rich side is required in order to perform CALPHAD thermodynamic modeling for a reliable database. Further experiments are recommended to study the high-temperature phase equilibria between liquid, (γMn), (δMn) and Mn2Ga(h), phase reactions between Mn8Ga5 and Mn7Ga6, and invariant reactions involving the MnGa phase. Nevertheless, the summarized information on phase equilibria, phase diagram, crystallography, magnetic transition temperature, magnetic moment, heat capacity, and enthalpy of formation can support the future thermodynamic investigation of the Mn–Ga system, which is critical for the materials design and discovery of Ni–Mn-Ga alloys.

Phase Diagram and Magnetocaloric Effect of Mn2Tb-Fe2Tb System

Mn2Tb-Fe2Tb phase diagram was drawn, and the crystal structure and magnetocaloric effect of (Mn1-xFex)2Tb (x ≤ 0.5) compounds at the Mn-rich side were systematically studied. X-ray diffraction demonstrates that all these Laves phase compounds crystallize in the cubic MgCu2-type structure. The Rietveld results of XRD shows the cell volume increases with Fe content. The influence of doping effect in (Mn1-xFex)2Tb (x ≤ 0.5) compounds on their magnetic and magnetocaloric properties for all solid solutions is presented. The Curie temperature (Tc) rises from 49 K (for x = 0.0) to 322 K (for x = 0.5), depending on Fe content significantly. Based on Landau’s theory, the magnetization behavior and magnetic transition were analyzed. The magnetocaloric effect (MCE) of (Mn1-xFex)2Tb compounds is also discussed using the Maxwell relation, and the maximum magnetic entropy change (− ΔSMMax) approaches to 10 J kg−1 K−1 at x = 0 under a field ranging from 0 to 5 T. The best relative cooling power (RCP) reaches 535.03 J/kg (x = 0.1).

Quasi-one-dimensional magnetism in [formula omitted] compounds: From Heisenberg to Ising chains

A series of MnxFe1-xNb2O6 compounds (0⩽x⩽1) is investigated by both X-ray and neutron powder diffraction, as well as specific-heat and magnetic measurements. The samples present orthorhombic Pbcn crystal symmetry, and exhibit weakly coupled magnetic chains. These chains are of Heisenberg type (weak anisotropy) on the Mn-rich side, and Ising-like (strong anisotropy) on the Fe-rich side. Except for 100% Fe (x=0), which has weakly-interacting ferromagnetic Ising chains, a negative Curie-Weiss temperature is obtained from the magnetic susceptibility, indicating dominant antiferromagnetic interactions. At the lowest probed temperature, T=1.5K, true long-range magnetic order is only observed for x=1, 0.8, and 0. Although the ordering is globally antiferromagnetic in all cases, the first two are characterized by a two-sublattice structure with propagation vector k=(0,0,0), while the latter presents alternatingly oriented ferromagnetic chains described by k=(0,12,0). For other compositions, short-range magnetic correlations are extracted from diffuse neutron-scattering data.

Crystal structure, homogeneity range and electronic structure of rhombohedral γ-Mn5Al8

Abstract The γ-region of the Mn–Al phase diagram between 45 and 70 at.% Al was re-investigated by a combination of powder and single crystal X-ray diffraction as well as EDS analysis to establish the distribution of Mn and Al atoms. Single crystals of γ-Mn5–x Al8+x were grown using Sn-flux at 650 °C. The crystal structure, atomic coordinates and site occupancy parameters of γ-Mn5−x Al8+x phases were refined from single crystal X-ray data. The γ-Mn5-x Al8+x phase adopts the rhombohedral Cr5Al8-type structure rather than a cubic γ-brass structure. The refined compositions from two crystals extracted from the Al-rich and Mn-rich sides are, respectively, Mn4.76Al8.24(2) (I) and Mn6.32Al6.68(2) (II). The structure was refined in the acentric R3m space group (No.160, Z=6), in order to compare with other reported rhombohedral γ-brasses. In addition, according to X-ray powder diffraction analysis, at the Al-rich side the γ-phase coexists with LT–Mn4Al11 and, at the Mn-rich side, with a hitherto unknown phase. The refined lattice parameters from powder patterns fall in the range a=12.6814(7)−12.6012(5) Å and c=7.9444(2)−7.9311(2) Å from Al-rich to Mn-rich loadings, and the corresponding rhombohedral angles distorted from a pseudo-cubic cell were found to be 89.1(1)°−88.9(1)°. Magnetic susceptibility and magnetization studies of Mn4.92Al8.08(2) are consistent with moment bearing Mn and suggest a spin glass state below 27 K. Tight-binding electronic structure calculations (LMTO-ASA with LSDA) showed that the calculated Fermi level for γ-“Mn5Al8” falls within a pseudogap of the density of states, a result which is in accordance with a Hume-Rothery stabilization mechanism γ-brass type phases.

Composition effects of spinel MnxCo3−xO4 nanoparticles on their electrocatalytic properties in oxygen reduction reaction in alkaline media

In this work, we synthesized a series of manganese cobalt spinel oxide (MnxCo3−xO4) nanoparticles (NPs) covering the whole composition range (x = 0.0. 0.4, 0.8, 1.4, 1.9, and 3.0) and investigated their electrocatalytic properties in relation with the oxygen reduction reaction (ORR) in alkaline media. The NP samples were synthesized by sonochemical reactions of Mn(OAc)2 and Co(OAc)2 (Ac = acetyl) in a water-dimethylformamide mixed solvent. The four samples in the Co-rich side have the cubic structure whereas the other two samples in the Mn-rich side have the tetragonal structure. The X-ray photoelectron spectroscopy and electrochemical analyses data indicate that the distribution of manganese and cobalt ions between the two metal ion sites of the spinel structure in our NP samples conforms to that of the bulk counterparts in the literature. The electrocatalytic data show that the ORR mechanism is changed when the structure is changed from cubic to tetragonal. The highest ORR activity was observed with the x = 0.4 sample. The electrochemical stability of this sample is higher than that of commercial Pt/C.

Experimental investigation of the Mg–Mn–Nd isothermal section at 450 °C

The Mg–Mn–Nd isothermal section at 450°C was constructed experimentally using solid–solid diffusion couples and key alloys. Diffusion couples and key alloys were annealed at the same temperature for different annealing time periods to understand the diffusion behavior of the system components, and to achieve the phase equilibrium in the system. The phase relations and solubility limits were determined using scanning electron microscope coupled with wave/energy dispersive X-ray spectrometers, X-ray diffraction and metallography. No ternary compounds could be observed in this system at 450°C. The microstructures of the diffusion zones showed Mn either as a pure element or as a solute atom. However, microstructures of the annealed key alloys near the Mn-rich side showed the formation of Mn17Nd2 at 450°C. Other Mn binary compounds, Mn2Nd and Mn23Nd6, were observed only in the as-cast alloys, because they are not stable at 450°C. The experiments showed that Mn remained stationary in some diffusion zones forming Mn+(MgNd), Mn+(Mg3Nd) and Mn+Mg41Nd5 two-phase regions. However, some of Mn atoms were diffusing in the system forming a continuous thin layer of pure Mn at the interface of pure Mg end-member, or to form (α-Nd)Mg,Mn, (MgNd) and (Mg3Nd) ternary solid solutions. The solubility of Mn in these solutions was estimated as 3.0, 13.0 and 3.5at.% Mn, respectively. Since Mn is in equilibrium with most of the phases in the system, the phase boundary lines are pointing toward Mn-rich corner except that of (α-Nd)Mg,Mn+(MgNd)+Mn17Nd2 three-phase field. This was confirmed based on the consistency of the results obtained from diffusion couples and key alloys.

Experimental investigation and first-principle calculations coupled with thermodynamic modeling of the Mn–Nd phase diagram

The complete Mn–Nd phase diagram was established experimentally by means of key samples and diffusion couple techniques. The phase transformation temperatures, crystal structures and phase equilibria were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and scanning electron microscope (SEM) techniques. Three compounds in the Mn-rich side and two terminal solid solutions in the Nd-rich side were observed. The compounds Mn 2 Nd, Mn 23 Nd 6 , and Mn 17 Nd 2 form peritectically at 850, 940, and 1025 °C, respectively. The eutectoidal decompositions of the compounds, Mn 2 Nd, and Mn 23 Nd 6 , were confirmed in the temperature ranges of 650–550 and 550–400 °C, respectively, using EPMA. The maximum solubility of Mn in DHCP-Nd was found to be 2.3 at% Mn at the 685 °C eutectic temperature. The solvus line of DHCP-Nd was determined using EPMA. The solubility of Mn in BCC-Nd was extrapolated from DSC data to be 5.0 at% Mn at 728 °C. The existence of a Mn 17 Nd 2 phase of the Th 2 Ni 17 type structure was confirmed using EPMA and XRD. The system was modelled using CALPHAD methodology. The quasi-chemical model (QCM) was used to describe the liquid phase, the terminal solution phases were modeled as substitutional solutions using the random mixing model, and the intermetallic compounds were treated as stoichiometric phases. The enthalpies of formation of the system compounds were calculated using the electronic density functional method. The resulting enthalpy of mixing was in good agreement with the literature. • The Mn–Nd phase diagram has been constructed experimentally. • First-principle calculations coupled with thermodynamic modeling have been performed. • A self-consistent set of parameters have been obtained using CALPHAD approach. • Modified quasi-chemical model has been used to model the liquid phase.

Ab initiostudy of ground-state properties of the Laves-phase compoundZrMn2

By an ab initio density functional approach the structural and phase stability, electronic and magnetic properties, elastic constants, phonon dispersion, and defect formation of the Laves-phase compound $\mathrm{Zr}{\mathrm{Mn}}_{2}$ for the C15, C14, and C36 crystal structures were investigated. In order to study the stability of magnetic phases, nonmagnetic and spin polarized calculations for ferro- and antiferromagnetic orderings were performed. At low temperatures, the ferromagnetic cubic C15 phase was obtained as the ground state, with the ferromagnetic hexagonal C14 and C36 phases being almost degenerate in energy. From the calculated temperature-dependent free energies a structural transformation from C15 to C14 at about ${T}_{tr}=200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is predicted, confirming the experimentally observed C14 structure at elevated temperatures. Elastic properties were investigated for the nonmagnetic and ferromagnetic C14 and C15 phases. Structural stability studies based on the calculated temperature-dependent free vibrational energies very strongly favor the existence of ferromagnetic phases. Point defect formation properties for vacancies and antiste defects were calculated by combining a supercell approach with a statistical mechanics model. Mn antisites are the most favorable defects broadening the homogeneity range of the $\mathrm{Zr}{\mathrm{Mn}}_{2}$ phase toward the Mn-rich side. The existence of ordered Mn-rich compounds is predicted. Large magnetic moment of $3\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ for Mn antisite defects are derived.

Electric transport and magnetic properties of perovskitesLaMn1−xCoxO3 up to 900 K

The structural, magnetic and transport properties of theLaMn1−xCoxO3 system were investigated over a wide temperature range, 10–900 K. Two structural types, depending onx, weredetected—orthorhombic Pbnm () and rhombohedral (x>0.6), separated by thebi-phasic sample x = 0.6.At both ends of the LaMn1−xCoxO3 system, the respective substituents are unambiguously characterized asCo2+ () and Mn4+ (). On the Mn-rich side, up to x<0.5, we infer on the basis of high temperature transport and magnetic data the gradual increase of theCo2+ valence towardsthe prevailing Co3+, while for the Co-rich samples (), the Co3+ states tend to disproportionate at high temperatures toCo2++Co4+, which probably controls both the transport and magnetic properties. At low temperatures,the long range ferromagnetic order was confirmed by means of neutron diffraction for thex = 0.4 sample. A non-uniform magnetic state was detected at higher cobalt substitution up tox = 0.8 and was associated with FM clusters that are formed below K and coagulate below K.

On the magnetic phase transition in Fe xMn 1 −xSi

The pseudobinary series Fe x Mn 1− x Si shows a transition from an insulator for x=1 to a metallic state with long range magnetic order at the Mn-rich side. In order to understand the mechanism of the magnetic phase transition, we perform ab initio calculations for the electronic band structure and the magnetic properties of Fe x Mn 1− x Si. The calculations are based on density-functional theory with the local-spin-density approximation. The pressure effect on the magnetic properties of MnSi are calculated. It is found that the magnetic phase transition can be attributed to the hybridization among Mn 3d, Fe 3d and Si 3p orbitals.

(Fe,Mn) Si: Transitions from a magnetic to a nonmagnetic state and from metallic to semiconducting behaviour

The pseudobinary series (FexMn1-x)Si shows a transition from an insulator for x = 1 to a metallic state with long range magnetic order at the Mn-rich side. This behaviour can be attributed to the shift of the Fermi energy across a narrow gap into a region of high density of states.

Magnetic properties and phase diagram of Ni xMn 1− xTiO 3

A mixed compound Ni x Mn 1− x TiO 3 with exchange frustrations and competing anisotropies was studied by de-magnetization and neutron scattering measurements, and the concentration versus temperature phase diagram was established. A variety of magnetic phases, including a spin glass phase and the mixed phases reentered from the antiferromagnetic ones, appear on both sides of the SG phase. In addition we found that the spin direction in the AF phase on the Mn rich side rotated from the c-axis to the c-plane, whereas it rotated again from the c-plane to the c-axis in the mixed phase.

Phase diagram and reentrant spin-glass behavior in a random mixture of two Ising-antiferromagnets Fe xMn 1−xTiO 3

Low-field DC susceptibility measurements have been made on a random-mixture of two Ising-antiferromagnets Fe xMn 1−xTiO 3. A spin-glass state appears in a wide range of intermediate concentration. In samples with certain x in the Fe-rich side or the Mn-rich side, the reentrant transition from the antiferromagnetic state or the random-antiferromagnetic state is found to occur. The reentrant behavior appears drastically, which we attribute to the strong frustrations existing in a magnetically non-diluted short-range system. The concentration versus temperature phase diagram is also shown.

Magnetic properties of the intermetallic compounds Gd(Mn1−xNix)2

The magnetic properties of pseudobinary compounds Gd(Mn1−xNix)2 were studied to understand the type of magnetic interaction among the constituent atoms of the parent binary compound. The Arrott plot for GdMn2 indicates no spontaneous magnetization. The magnetization and the Curie temperature increase with increasing concentration of Ni on the Mn rich side. The collapse of the Mn moment makes the Gd moment dominant in magnetization with increasing Ni concentration.

Aufbau und magnetische Eigenschaften manganreicher Cu-Mn- und Mn-Sn-Legierungen

The phase equilibria on the Mn-rich side of the systems Cu-Mn and Mn-Sn were determined by susceptibility measurements at high temperatures. The phase relationships observed on the Mn-rich side of the system Cu-Mn as well as the susceptibility transformation diagram are in good accordance with the phase diagrams given in the literature. According to our measurements in the system Mn-Sn the δ-Mn phase field extends to about 10.2 at.% Sn at 1 302 K. The γ-Mn phase ranging to 7.5 at.% Sn was found to decompose eutectoidally at 1 315 K. The peritectic formation of the hexagonal phase with the approximate composition of Mn3Sn occurs at 1 257 K. The Mn-rich boundary of the two-phase field β-Mn+Mn3Sn is located at about 10 at.% Sn.

Occurrence of magnetic order in a pseudobinary system of non-magnetic binaries: YMn2-2cCo2c

The pseudobinary system YMn2-2cCo2c is shown to develop ferromagnetic order over a limited range of composition. This is explained on the basis of ferromagnetic Mn-Mn coupling in the large c limit, using a local model for exchange. Behaviour reminiscent of a spin glass develops at the Mn-rich side of the homogeneous range. A weak intrinsic coercivity exists at 4.2K, but no mictomagnetic asymmetry of the hysteresis is observed.

The solvus in the system MnCO3-CaCO3

The solvus on the Mn-rich side in the system MnCO3-CaCO3 was studied experimentally at 10 kb and lower pressures. The critical point lies at 540 °C and Mn0.68Ca0.32CO3. Reaction rates of demising are extremely sluggish. X-ray calibration curves for (Mn, Ca)CO3 solid solutions are given. Depicting microprobe analyses of about 300 carbonates from manganese calc silicate marbles affected by different degrees of metamorphism confirm the experimentally derived solvus. Margules parameters were derived from the experimental solvus, giving for spinodal unmixing W a=20.1+0.032·T and W b=18.3-0.0033·T, and for binodal unmixing W a=−22.9+0.035 ·T and W b=3.36+0.0147·T (All W, in kJ/-mol) A physical interpretation of the Margules parameters based on deformations of the ionic radii in the solid solution is presented. The Margules parameters obtained by this model agree fairly well with the experimental data.

A X-RAY INVESTIGATION OF THE MANGANESE-GALLIUM SYSTEM

Debye-Scherrer photographs have been taken from forty-four slowly cooled and quenched manganese-gallium alloys. These, incorporated with the differential thermal analysis taken at the gallium-rich side, provide a basis for the Mn-Ga constitutional diagram.There are ten different phases beside pure Ga in the entire system. The solid solubility of Mn in Ga is almost undetectable. The α phase is the primary solid solution of Ga in α-Mn. The solubility limit at room temperature is 1.95 at % Ga. The β phase has a homogeneity range from 8.6 to 19.2 at % Ga at room temperature. The structure is that of β-Mn. It may be looked upon as a solid solution of Ga in β-Mn, stabilized at room temperature due to the random substitution of some of the Mn atoms by Ga. The γ phase may be divided into three parts, γ1, γ2, and γ3. γ1 is face-centred cubic, γ2, face-centred tetragonal, while γ3, face-centred tetragonal with a long range order. The structure of γ3 is isomorphous with CuAu I in the Cu-Au system. γ3 is stable at room temperature, the homogeneity range being from 37 to 45 at% Ga; while γ1 is only stable at high temperatures. The transformations from γ1 to γ2 and then to γ3 are of the second degree, the degree of order increasing with the Ga content and decreasing with the temperature. The whole phase γ may be considered as a solid solution of Ga in γ-Mn, which could not be retained by quenching in the pure state. The δ phase exists only at high temperatures. It may be regarded as a solid solution of Ga in δ-Mn, deformed and ordered by the substitution of some of the Mn atoms by Ga. The ε phase has an ordered hexagonal close-packed structure with eight atoms per unit cell. It is formed congruently from the y phase at about 820℃. The homogeneity range at room temperature is estimated to be from 27 to 30 at% Ga. The η phase has a wide range at room temperature, estimated to be from 50 to 60 at% Ga. From 520 to 600℃, it undergoes a polymorphic transformation to another phase λ, the homogeneity range of which being displaced with temperature toward the Mn-rich side. Both η and λ indicate quite complicated structures. At the Ga-rich side, there are three intermediate phases x, φ and ω. They are formed by peritectoid or peritectic reactions. The ideal structure of φ is cubic of the NiHg4 type, but it lies outside of the very narrow homogeneity range around Mn2.3 Gay7.7. Most probably the stoichiometric composition of the ω phase is Mn2Ga9 or MnGa5. Among the six intermediate phases stable at room temperature, β, ε, γ3, x and φ are ferromagnetic. The most pronounced ferromagnetic alloys have been found in the γ3 and φ regions which are rich in Ga content. Saturation magnetizations and Curie points for some of the alloys have been determined.

Magnetic properties of MnAl system alloys

The ferromagnetic phase of MnAl alloy exists at a position slightly different from that of Mn:Al = 1:1 toward the Mn rich side. The single crystal of MnAl alloy was prepared by the horizontal type zone melting process. Domain patterns of that single crystal were observed microscopically with or without applying the magnetizing field, using a colloidal solution of fine iron oxide powders. Domain patterns on the ferromagnetic phase are similar to those of cobalt and MnBi alloy. From magnetizing curves measured at room temperature, the saturation magnetization ( 4\piIs ) was found to be 6900 gauss and then crystalline anisotropy constant K was calculated to be 9.3 \times 10^{6} ergs/cm3. When cooled from the room temperature to -140° C, 4\piIs and K were hardly varied, but the both parameters were slightly decreased when heated up to about 60°C. MnAl alloy properties are magnetically excellent in themselves, but it is very interesting to note that they are remarkably improved by adding up to two percent boron. The improved magnetic characteristics are as follows: 1) Ferromagnetic phase is present in the sample of water-quenched state after a solid solution treatment of 1100°C; 2) Needle-shaped crystals are precipitated into the matrix as the secondary ferromagnetic phase; 3) The more the ternary MnAl-B alloys are swaged, the better magnetic properties are gained, for example, Br 5900 G, B H c 1780 Oe, and (BH)max 3.5 M.G.Oe at 70 percent reduction of 71.0 percent Mn, 26.65 percent Al, 1.76 percent B alloy.