Mn Distance Research Articles

Magnetic Properties in Mn-Doped δ-MoN: A Systematic Density Functional Theory Study.

Due to the potential applications of transition metal nitrides in modern electronic and spintronic devices, we have systematically studied the magnetic properties of δ-MoN induced by the Mn dopant, with the goal of identifying the origin of magnetism and figuring out the magnetic coupling mechanism between the Mn dopants. Based on the density functional theory, one Mn atom doped at different Mo sites (2a and 6c in the International Tables) in the unit cell of δ-MoN was firstly studied. It was found that the Mn dopant located at the 2a or 6c site leads to significant spin splitting of the density of states, suggesting that the Mn doping induces magnetism in δ-MoN. The calculations were then extended to a 2 × 1 × 2 supercell, which contains two impurity Mn atoms. Detailed analysis reveals that the different couplings of the Mn–Mn pair cannot be simply attributed to the different Mn–Mn distances but are closely related to the electronic processes that take place in the segment (–N– or –N–Mo–N–) that connects two Mn dopants. The mechanisms responsible for the FM/AFM coupling of the Mn–Mn pairs are the superexchange and the p–d exchange mediated by the N atoms, and the d–d coupling between the host Mo atom and the Mn dopant.

Effect of thermal stress on non-collinear antiferromagnetic phase transitions in antiperovskite Mn3GaN compounds with Mn3SbN inclusions

In the designed (1-x)Mn3GaN-xMn3SbN (0.2 ≤ x ≤ 0.8) heterogeneous system, modulating the non-collinear antiferromagnetic (AFM) phase transitions of antiperovskite Mn3GaN using thermal stress is realized for the first time. With growing the Mn3SbN secondary phase, the Neel temperature (TN) of Mn3GaN phase shifts down by 40 K and then disappears, but another magnetic transition below TN appears and shifts up by 125 K. The neutron powder diffraction (NPD) results of the sample with x = 0.6 show that the magnetic transition below TN ascribed to the decreasing Mn–Mn distance (dMn–Mn) and spin re-orientation from Γ5g to a new non-collinear M2 AFM phase. By the NPD analysis, the dMn–Mn of the Mn3GaN phase decreases from 2.75527(4) Å to 2.73925(3) Å, and the angles of the spin rotations for Mn1/Mn2, Mn3-1, and Mn3-2 atoms in M2 AFM during the spin re-orientation process are 90°, 60°, and 60°, respectively. Negative thermal expansion behaviors and caloric effects associated with Γ5g phase transitions are investigated systematically. Further, the thermal stress could be regulated by adjusting the proportion of Mn3GaN and Mn3SbN phases with mismatched thermal expansion, which could be estimated even up to GPa according to Clausius–Clapeyron relation.

CaMn7O12 Quadruple Perovskite Oxides Proceed by Two‐Active‐Site Reaction Mechanism for the Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) is one of the essential energy conversion reactions for hydrogen production. In quadruple perovskite oxides AA’3B4O12 (A=Ca, Sr, A’=Cu, Mn and B=3d metals), the new reaction mechanism of O−O bond formation between adsorbed oxygen species at adjacent A’‐B sites has been proposed in recent studies. This idea of multiple transition metals working together to form an active site, rather than a single active site, is appealing, but has not been systematically investigated so far. This study examined catalytic OER performances of CaMn7O12 quadruple perovskite oxides with precisely controlled Mn(A′)−Mn(B) distance by doping with Sr, Cu and Al. The crystal structure and the state of cations and O were investigated through XRD with Rietveld refinement and X‐ray absorption spectroscopy. The OER catalytic activity is clearly correlated with the distance of Mn(A’)−Mn(B) while both eg state of Mn and O 2p band center unchanged. The shrinkage of the A’‐B distance affects the stability of O−O bond on A’‐B site and accelerates OER kinetics.

Synthesis, crystal structure and magnetic properties of a one-dimensional Mn2+ complex constructed from (+)-dibenzoyltartaric acid and 2,2'-bipyridine.

The self-assembly reaction of (+)-dibenzoyltartaric acid (D-H2DBTA) with 2,2'-bipyridine (bpy) and Mn(CH3CO2)2·4H2O yielded a new coordination polymer, namely, catena-poly[[[diaqua(2,2'-bipyridine-κ2N,N')manganese(II)]-μ-2,3-bis(benzoyloxy)butanedioato-κ2O2:O3] dihydrate], {[Mn(C18H12O8)(C10H8N2)(H2O)2]·2H2O}n or {[Mn(DBTA)(bpy)(H2O)2]·2H2O}n, (I). Complex (I) has been characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA) and single-crystal and powder X-ray diffraction. It crystallizes in the orthorhombic space group P212121. In the complex, the Mn2+ cation displays a distorted octahedral {MnO4N2} geometry, formed from two carboxylate O atoms of two DBTA2- ligands, two cis-oriented N atoms from one chelating 2,2'-bipyridine ligand and two trans-oriented O atoms from coordinated water molecules. The polymer displays a 1D chain with an Mn...Mn distance of 9.428 (1) Å. Due to the presence of flexible polycarboxylate and rigid bipyridyl ligands in the molecular structure, a high thermal stability of the complex is attained. The magnetic properties of (I) were analyzed based on the mononuclear Mn2+ model due to the long intramolecular Mn...Mn distance. The zero field splitting (ZFS) contribution in the high-spin Mn2+ cation is almost negligible and there are weak antiferromagnetic couplings between 1D chains [zJ' = -0.062 (5) cm-1], corresponding to an intermolecular Mn...Mn distance of 7.860 (2) Å.

Photoluminescence of pefloxacindi-ium manganese(II) and zinc(II) tetrahalides

Mn2+-based hybrid materials have become the hotspot of current research studies owing to their high photoluminescence quantum yield (PLQY), low-cost, environmental friendliness and stability. For the first time, we report the hydrothermal synthesis of two lead-free zero-dimensional luminescent organic-inorganic hybrid compounds, PefH2[MnBr4] (1) and PefH2[MnCl4] (2) (Pef = pefloxacin). They were characterized by elemental analysis, TG-DSC, single-crystal and powder XRD. Compounds 1–2 exhibit a distorted tetrahedral geometry around the manganese(II) metal center, which is isolated from the same centers by bulky pefloxacindi-ium (PefH22+) ions with a Mn···Mn distance of 7.3 Å. Their structures are stabilized by N—H···O, O—H···X (X = Br, Cl), C—H···O and C—H···X hydrogen bands and π–π stacking interaction. Thermal decomposition starts at T > 230°С for 1 and T > 210°С for 2 and proceeds for several stages. Upon UV excitation compounds exhibit a bright green emission with a moderate PLQY of 45% for 1 and 30% for 2. The influence of the halide ion and metal ion on the photoluminescence properties of isostructural compounds PefH2[MX4] (M = Mn, Zn and X = Br, Cl) is discussed.

Magnetic Structure of Short-Range Ordering in Intermetallic Antiferromagnet Mn3RhSi

Magnetic pair distribution function (mPDF) of intermetallic antiferromagnet Mn3RhSi is estimated from the powder neutron diffraction data. The mPDF exhibits negative peak at about r = 2.7 Å corresponding to the nearest neighbor Mn–Mn distance above the antiferromagnetic transition temperature TN. Below TN, the mPDF is a superposition of the mPDF with the negative peak at about r = 2.7 Å and the mPDF calculated from the antiferromagnetic structure which is determined by the previous neutron diffraction study, indicating the coexistence of the short range ordering and the antiferromagnetic long range ordering. The mPDF of the short range ordering is not reproduced by the magnetic structure model with the symmetry consistent with that of the crystal structure. The possible magnetic structure which can reproduce the observed mPDF of the short range ordering is proposed.

Hardness, magnetic, elastic, and electronic properties of manganese semi-boride synthesized by high pressure and high temperature

Transition metal (TM) interaction induces many fantastic properties in transition metal light element compounds (TMLEs). Here, we report the synthesis of polycrystalline Mn2B specimen with strong Mn–Mn interaction by high pressure and high temperature (HPHT) method. Magnetic characterization gives anti-ferromagnetic and spin-glass behavior with Néel temperature of 43 ​K. Micro-hardness measurement yields an asymptotic Vickers hardness of 14.1 ​GPa which is far higher than manganese metal. To interpret the mechanical and magnetic properties, the chemical bond and electronic structure were investigated by first principle calculation. Although the distance between manganese atoms has been enlarged by inserting boron atoms, anti-ferromagnetic behavior is attributed to the insufficient Mn–Mn distance enlargement. Based on the bonds character, these manganese atoms layers are pinned together by quasi-boron-chains which is contradictory with fully isolated boron atoms configuration. Quasi-covalent boron chains and partial covalent Mn–B bonds attribute to its high hardness. Tuning Mn–Mn interaction is demonstrated as a promising method to modulate d-electron related magnetic and hardness property.

Spontaneous Formation of an Fe/Mn Diamond Core: Models for the Fe/Mn Sites in Class 1c Ribonucleotide Reductases.

A handful of oxygen-activating enzymes has recently been found to contain Fe/Mn active sites, like Class 1c ribonucleotide reductases and R2-like ligand-binding oxidase, which are closely related to their better characterized diiron cousins. These enzymes are proposed to form high-valent intermediates with Fe-O-Mn cores. Herein, we report the first examples of synthetic Fe/Mn complexes that mimic doubly bridged intermediates proposed for enzymatic oxygen activation. Fe K-edge extended X-ray absorption fine structure (EXAFS) analysis has been used to characterize the structures of each of these compounds. Linear compounds accurately model the Fe···Mn distances found in Fe/Mn proteins in their resting states, and doubly bridged diamond core compounds accurately model the distances found in high-valent biological intermediates. Unlike their diiron analogues, the paramagnetic nature of Fe/Mn compounds can be analyzed by EPR, revealing S = 1/2 signals that reflect antiferromagnetic coupling between the high-spin Fe(III) and Mn(III) units of heterobimetallic centers. These compounds undergo electron transfer with various ferrocenes, linear compounds being capable of oxidizing diacetyl ferrocene, a weak reductant, and diamond core compounds being capable of oxidizing acetyl ferrocene. Diamond core compounds can also perform HAT reactions from substrates with X-H bonds with bond dissociation free energies (BDFEs) up to 75 kcal/mol and are capable of oxidizing TEMPO-H at rates of 0.32-0.37 M-1 s-1, which are comparable to those reported for some mononuclear FeIII-OH and MnIII-OH compounds. However, such reactivity is not observed for the corresponding diiron compounds, a difference that Nature may have taken advantage of in evolving enzymes with heterobimetallic active sites.

A Distinct Spin Structure and Giant Baromagnetic Effect in MnNiGe Compounds with Fe-Doping.

Spin structure of a magnetic system results from the competition of various exchange couplings. Pressure-driven spin structure evolution, through altering interatomic distance, and hence, electronic structure produces baromagnetic effect (BME), which has potential applications in sensor/actuator field. Here, we report a new spin structure(CyS-AFMb) with antiferromagnetic(AFM) nature in Fe-doped Mn0.87Fe0.13NiGe. Neutron powder diffraction (NPD) under in situ hydrostatic pressure and magnetic field was conducted to reveal the spin configuration and its instabilities. We discovered that a pressure higher than 4 kbar can induce abnormal change of Mn(Fe)-Mn(Fe) distances and transform the CyS-AFMb into a conical spiral ferromagnetic(FM) configuration(45°-CoS-FMa) with easily magnetized but shortened magnetic moment by as much as 22%. The observed BME far exceeds previous reports. Our first-principles calculations provide theoretical supports for the enhanced BME. The compressed lattice by pressure favors the 45°-CoS-FMa and significantly broadened 3d bandwidth of Mn(Fe) atoms, which leads to the shortened magnetic moment and evolution of spin structure.

Extended “orbital molecules” and magnetic phase separation in Bi0.68Ca0.32MnO3

The low-temperature structure of ${\mathrm{Bi}}_{0.68}{\mathrm{Ca}}_{0.32}{\mathrm{MnO}}_{3}$ has been solved from electron and neutron diffraction data. The quantitative simultaneous refinement indicates an ordering of the Mn cations in a ``stripe/chess''-like pattern. The ordering is accompanied by the formation of short Mn---Mn distances and the rearrangement of the Mn---O bonds indicating the development of complex extended ``orbital molecules.'' The primary order parameter breaks inversion symmetry and allows the generation of a spontaneous electrical polarization as the secondary order parameter. The neutron data at low temperature indicate the coexistence of a pseudo-CE long-range-ordered structure with a strongly reduced moment and short-range ferromagnetic correlations. These results indicate an intricate competition between the charge, orbital, and magnetic degrees of freedom and the ${\mathrm{Bi}}^{3+}$ stereoactivity in this manganite system.

Design of Mn–Mn distance for tunable spontaneous exchange bias in Heusler alloys

To accelerate the discovery of spontaneous exchange bias (SEB) materials and optimize its performance, reasonable design scheme is needed. Taking advantage of the extremely sensitive dependence of SEB on the value of molecular magnetic moments in the Mn-rich Heusler alloys, a design scheme of the Mn–Mn distance for SEB is proposed to tune the molecular magnetic moment in the Ni-rich Heusler alloys. Here, it is found that the Mn–Mn distance can be controlled in the Ni2Mn1.4In0.6-xAlx system. The experimental results show that SEB is achieved in Ni2Mn1.4In0.6-xAlx (x = 0.24–0.56), and the SEB field is indeed dominated by the Mn–Mn distance. Therefore, the Mn–Mn distance can tune the molecular magnetic moment, and then tune SEB. Our findings demonstrate that the design of the Mn–Mn distance is an effective method to tune SEB. This opens up a new approach to the development of SEB materials.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Mn2+‐Doped Metal Halide Perovskites: Structure, Photoluminescence, and Application

AbstractDoping impurity ions into semiconductor luminescent materials offers a unique pathway for inducing new emission centers and enabling photoluminescence (PL) tuning. Among various luminescence materials, doping Mn2+ into metal halide perovskites becomes a hot topic since Mn2+ ions demonstrate an energy transfer route from host to dopants, resulting in interesting photophysical properties. This review aims to discuss the PL properties of Mn2+ ions in halide perovskites nanocrystals or bulk crystals with different structural dimensions and local environments (MnX42– tetrahedron, MnX62– octahedron, or shortest Mn─Mn distance). In this regard, the effects of Mn2+ doping on the PL properties and their modifications are summarized. Variable ion exchange dynamics, increased emission intensity, and enhanced stability induced by Mn2+ doping are analyzed. These results also provide beneficial insights into applications of the doped luminescent halide perovskites. Finally, the present challenges in Mn2+‐doped luminescent halide perovskites are elaborated.

Formation of Core-Shell Type Structure in Duplex Martensitic Steel

Microstructures of both as-quenched and intercritical-annealed medium-Mn steel were investigated by transmission electron microscopy to acquire a better understanding of γ–ɛ and γ–α′ martensitic transformations. The orientation relationships among each phases were determined as (-110)α′//(0001)ɛ, [111]α′//[11-20]epsiron for the case of as-quenched sample, and (-110)α′//(-111)γ//(0001)ɛ, [111]α′//[110]γ//[11-20]ɛ for the case of intercritical-annealed sample, respectively. In addition, the presences of core-shell type microstructures were confirmed with ɛ–martensite being surrounded by γ–austenite. Mn content of phases were found dependent on the solubility limit of Mn of phases by the combination of scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. The γ–austenite grow further by the shifting the interface between γ–austenite and α'–martensite, and forming of Mn depletion zone. Furthermore, the estimated diffusion distance of Mn within with γ–austenite was calculated about 25 nm.

Design Principles for Enhancing Photoluminescence Quantum Yield in Hybrid Manganese Bromides.

Hybrid manganese halides have attracted widespread attention because of their highly emissive optical properties. To understand the underlying structural factors that dictate the photoluminescence quantum yield (PLQY) of these materials, we report five new hybrid manganese bromides with the general formula AmMnBr4 [m = 1 or 2, A = dimethylammonium (DMA), 3-methylpiperidinium (3MP), 3-aminomethylpiperidinium (3AMP), heptamethylenimine (HEP), and trimethylphenylammonium (TMPEA)]. By studying the crystal structures and optical properties of these materials and combining our results with the findings from previously reported analogs, we have found a direct correlation between Mn···Mn distance and the PLQY, where high PLQYs are associated with long Mn···Mn distances. This effect can be viewed as a manifestation of the concentration-quenching effect, except these are in stoichiometric compounds with precise interatomic distances rather than random alloys. To gain better separation of the Mn centers and prevent energy transfer, a bulky singly protonated cation that avoids H-bonding is ideal. We have demonstrated this principle in one of our newly reported material, (TMPEA)2MnBr4, where a PLQY of 70.8% for a powder sample and 98% for a large single crystal sample is achieved. Our study reveals a generalized method for improving PLQYs in hybrid manganese bromides and is readily extended to designing all varieties of highly emissive hybrid materials.

Comparison of two MnIVMnIV-bis-μ-oxo complexes {[MnIV(N4(6-Me-DPEN))]2(μ-O)2}2+ and {[MnIV(N4(6-Me-DPPN))]2(μ-O)2}2.

The addition of tert-butyl hydro-peroxide ( t BuOOH) to two structurally related MnII complexes containing N,N-bis-(6-methyl-2-pyridyl-meth-yl)ethane-1,2-di-amine (6-Me-DPEN) and N,N-bis-(6-methyl-2-pyridyl-meth-yl)propane-1,2-di-amine (6-Me-DPPN) results in the formation of high-valent bis-oxo complexes, namely di-μ-oxido-bis-{[N,N-bis-(6-methyl-2-pyridylmeth-yl)ethane-1,2-di-amine]-manganese(II)}(Mn-Mn) bis-(tetra-phenyl-borate) dihydrate, [Mn(C16H22N4)2O2](C24H20B)2·2H2O or {[MnIV(N4(6-Me-DPEN))]2(μ-O)2}(2BPh4)(2H2O) (1) and di-μ-oxido-bis-{[N,N-bis-(6-methyl-2-pyridylmeth-yl)propane-1,3-di-amine]-manganese(II)}(Mn-Mn) bis-(tetra-phenyl-borate) diethyl ether disolvate, [Mn(C17H24N4)2O2](C24H20B)2·2C4H10O or {[MnIV(N4(6-MeDPPN))]2(μ-O)2}(2BPh4)(2Et2O) (2). Complexes 1 and 2 both contain the 'diamond core' motif found previously in a number of iron, copper, and manganese high-valent bis-oxo compounds. The flexibility in the propyl linker in the ligand scaffold of 2, as compared to that of the ethyl linker in 1, results in more elongated Mn-N bonds, as one would expect. The Mn-Mn distances and Mn-O bond lengths support an MnIV oxidation state assignment for the Mn ions in both 1 and 2. The angles around the Mn centers are consistent with the local pseudo-octa-hedral geometry.

Effect of Ge substitution on the magnetocaloric effect and exchange bias in Mn–Ni–Sn-Ge alloys: The role of Mn–Mn distance

Abstract The effect of Ge substitution on the phase transitions, magnetocaloric effect, and exchange bias is studied in Mn50Ni40Sn10-xGex alloys by structural and magnetic analysis. Due to the lattice contraction induced by Ge substitution, the martensitic transformation temperature increases gradually, and the reentrant spin glass ground state is suppressed at x = 5 where zero-field-cooled exchange bias (ZEB) emerges. The maximum values of magnetic entropy change and ZEB are 19.2 J/kg·K for the field change of 5 T and 1.49 kOe at 10 K, which are achieved in Mn50Ni40Sn8Ge2 and Mn50Ni40Sn4Ge6, respectively. Importantly, the second-nearest Mn–Mn distance is found to be a key parameter affecting the magnetization change across the martensitic transformation and the ground state of these alloys. This work sheds new light on understanding the magnetism in Ni–Mn-based ferromagnetic shape memory alloys.

Magnetic and optical properties of δ-SnSe doped by transition-metal atoms: A first-principle calculation

By employing the first-principles calculations, the effect of transition-metallic doped δ-SnSe monolayer have been investigated. All considered transition-metal (TM, TM = Co, Cu, Mn, Fe, and Ni) dopants induce magnetic moment except for Cu. Based on the binding energies, the Mn- and Fe-doped systems are more structurally stable. We further study the magnetic coupling of these two systems. For the Mn-doped system, its antiferromagnetic (AFM) state is its ground state, and it changes to nonmagnetic (NM) sate as the Mn–Mn distance increases. Owing to the strong spin-orbit coupling between Fe-3d and Se-4p, different phenomena show in the Fe-doped system. Both AFM and ferromagnetic (FM) coupling is observed, which is mainly determined by the Fe–Fe distance and the crystal direction. Moreover, due to the introduction of Cu and Mn atoms, the absorption strength in visible light might be enhanced. These results show that the δ-SnSe monolayer doped with TM atoms might give some potential applications in spintronic devices and optical fields.

New Insights into Mn-Mn Coupling Interaction-Directed Photoluminescence Quenching Mechanism in Mn2+-Doped Semiconductors.

Strong Mn-Mn coupling interactions (dipole-dipole and spin-exchange), predominantly determined by statistically and apparently short Mn···Mn distances in traditional heavily Mn2+-doped semiconductors, can promote energy transfer within randomly positioned and close-knit Mn2+ pairs. However, the intrinsic mechanism on controlling Mn2+ emission efficiency is still elusive due to the lack of precise structure information on local tetrahedrally coordinated Mn2+ ions. Herein, a group of Mn2+-containing metal-chalcogenide open frameworks (MCOFs), built from [Mn4In16S35] nanoclusters (denoted T4-MnInS) with a precise [Mn4S] configuration and length-variable linkers, were prepared and selected as unique models to address the above-mentioned issues. MCOF-5 and MCOF-6 that contained a symmetrical [Mn4S] core with a D2d point group and relatively long Mn···Mn distance (∼3.9645 Å) exhibited obvious red emission, while no room-temperature PL emission was observed in MCOF-7 that contained an asymmetric [Mn4S] configuration with a C1 point group and relatively short Mn···Mn distance (∼3.9204 Å). The differences of Mn-Mn dipole-dipole and spin-exchange interactions were verified through transient photoluminescent spectroscopy, electron spin resonance (ESR), and magnetic measurements. Compared to MCOF-5 and MCOF-6 showing a narrower/stronger ESR signal and longer decay lifetime of microseconds, MCOF-7 displayed a much broader/weaker ESR signal and shorter decay lifetime of nanoseconds. The results demonstrated the dominant role of distance-directed Mn-Mn dipole-dipole interactions over symmetry-directed spin-exchange interactions in modulating PL quenching behavior of Mn2+ emission. More importantly, the reported work offers a new pathway to elucidate Mn2+-site-dependent photoluminescence regulation mechanism from the perspective of atomically precise nanoclusters.

Interface Characteristics and Properties of a High-Strength Corrosion-Resistant Stainless Steel Clad Rebar

This paper aims at manufacturing stainless steel clad (SSC) rebars by metal deposition and a hot rolling method as well as characterizing its interface features and mechanical properties. The interface of the SSC rebar is relatively flat and clean, exhibiting a metallurgical bonding state at the microscale. Decarburization occurred at the interface in the carbon steel side of the SSC rebar. The diffusion of C, Cr, as well as Mn was measured across the interface of the SSC rebar, and the diffusion distance of Cr and Mn was found at 32 µm and 25 µm, respectively. The Vickers hardness testing in the transition zone of the SSC rebar near the carbon side showed 545 HV0.2 due to the martensite phase formed by the diffusion of key elements C, Cr, and Mn. The microstructure in the transition zone near the stainless steel reveals the duplex structure of martensite and ferrite. The carbide precipitations were observed near the interface, both in the transition zone and in the base metal of the stainless steel zone. The yield strength, tensile strength, and elongation of the SSC rebar were found as 423 MPa, 602 MPa, and 22%. No macroscopic crack was observed after the positive or negative bending tests.