Mn Ir Research Articles

Rational Design of Ultrahigh-Loading Ir Single Atoms on Reconstructed Mn─NiOOH for Enhanced Catalytic Performance in Urea-Water Electrolysis.

Investigating advanced electrocatalysts is crucial for improving the efficacy of water splitting to generate environmentally friendly fuel. The discovery of highly effective electrocatalysts, capable of driving oxygen evolution reaction (OER) and urea oxidation reaction (UOR) in urea-alkaline environments, is pivotal for advancing large-scale hydrogen production. This study aims to introduce a new method that involves creating nanosheets of high-loading iridium single atoms embedded in a manganese-containing nickel oxyhydroxide matrix (Ir@Mn─NiOOH). These nanostructures are derived from self-supported hydrate pre-catalyst nanosheets grown on nickel foam and then activated through electrochemical etching pretreatment. The Ir@Mn─NiOOH nanoarchitecture displays outstanding electrocatalytic activity, having a low overpotential of just 258mV and a potential of 1.319V (at 10mAcm-2) for OER and UOR, respectively. Such extraordinary catalytic characteristics of Ir@Mn─NiOOH is mainly owing to the strong synthetic electronic interaction between Ir single atoms and Mn─NiOOH, which can change its electronic characteristics and boost electrochemical catalytic sites. This research presents a new way to produce exceptionally efficient catalysts by adding a synergistic effect to complex multi-electron processes.

Engaging Alkenes in Metallaphotoredox: A Triple Catalytic, Radical Sorting Approach to Olefin-Alcohol Cross-Coupling.

Metallaphotoredox cross-coupling is a well-established strategy for generating clinically privileged aliphatic scaffolds via single-electron reactivity. Correspondingly, expanding metallaphotoredox to encompass new C(sp3)-coupling partners could provide entry to a novel, medicinally relevant chemical space. In particular, alkenes are abundant, bench-stable, and capable of versatile C(sp3)-radical reactivity via metal-hydride hydrogen atom transfer (MHAT), although metallaphotoredox methodologies invoking this strategy remain underdeveloped. Importantly, merging MHAT activation with metallaphotoredox could enable the cross-coupling of olefins with feedstock partners such as alcohols, which undergo facile open-shell activation via photocatalysis. Herein, we report the first C(sp3)-C(sp3) coupling of MHAT-activated alkenes with alcohols by performing deoxygenative hydroalkylation via triple cocatalysis. Through synergistic Ir photoredox, Mn MHAT, and Ni radical sorting pathways, this branch-selective protocol pairs diverse olefins and methanol or primary alcohols with remarkable functional group tolerance to enable the rapid construction of complex aliphatic frameworks.

Constructing asymmetrical dual catalytic sites in manganese oxides enables fast and stable lithium–oxygen catalysis

A general asymmetrical dual-site (Mn–Ru or Mn–Ir) construction strategy on manganese oxides is demonstrated to significantly improve the oxygen catalytic activity and cycling stability toward lithium–oxygen batteries.

Amorphous mixed Ir–Mn oxide catalysts for the oxygen evolution reaction in PEM water electrolysis for H2 production

Proton exchange membrane (PEM) water electrolysis is a kind of green and sustainable hydrogen production technology. However, it is limited by sluggish kinetics of anodic oxygen evolution reaction (OER), and it is necessary to develop efficient, stable and economical catalysts. In this manuscript, amorphous mixed Ir–Mn oxide catalysts (IrMnOx) with different Mn contents are synthesized by simple low-temperature calcination. IrMnOx catalysts have poor crystallinity and abundant surface hydroxyl defects, which helps improve catalytic activity and electrochemical stability for acidic OER. Compared with commercial rutile IrO2, they show lower overpotential and higher current density. Among the prepared catalysts, Ir0·6Mn0.4Ox and Ir0·7Mn0.3Ox perform best, and overpotentials are only 212 mV at the current density of 10 mA/cm2 and 263 mV at 100 mA/cm2, and there is no obvious activity decay after the 8-h stability experiment. IrMnOx catalysts reported provide hope for high-efficiency oxygen evolution reaction in PEM water electrolysis.

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Charge-transfer driven ferromagnetism in a disordered three-dimensional 3d-5d spin system

A three-dimensional disordered spin system consisting of 3d transition metal ion Mn4+ with strong electronic correlations and heavy 5d transition metal ion Ir4+ has been investigated in form of a perovskite thin film. The studied compound of the composition SrMn0.5Ir0.5O3 does not exist as bulk or single crystal, but can be stabilized by epitaxy onto SrTiO3 single crystals as fully disordered double perovskite by pulsed laser deposition. As measured by X-ray circular dichroism, the ground state of this material is ferromagnetic with both, Mn and Ir, spins aligned in parallel. This unusual ground state can be qualitatively explained by charge-transfer driven magnetic exchange involving Mn eg-state and Ir t2g-state, with no evidence of spin–orbit coupling in Ir. Due to the coexistence of competing magnetic interactions and randomness in the system, spin-glass features are observed at low temperatures.

Synthesis, Crystal Structure, and Compressibilities of Mn3-x Ir5 B2+x (0≤x≤0.5) and Mn2 IrB2.

The new ternary transition metal borides Mn3‐xIr5B2+x (0≤x≤0.5) and Mn2IrB2 were synthesized from the elements under high temperature and high‐pressure/high‐temperature conditions. Both phases can be synthesized as powder samples in a radio‐frequency furnace in argon atmosphere. High‐pressure/high‐temperature conditions were used to grow single‐crystals. The phases represent the first ternary compounds within the system Mn–Ir–B. Mn3−xIr5B2+x (0≤x≤0.5) crystallizes in the Ti3Co5B2 structure type (P4/mbm; no. 127) with parameters a=9.332(1), c=2.896(2) Å, and Z=2. Mn2IrB2 crystallizes in the β‐Cr2IrB2 crystal structure type (Cmcm; no. 63) with parameters a=3.135(3), b=9.859(5), c=13.220(3) Å, and Z=8. The compositions of both compounds were confirmed by EDX measurements and the compressibility was determined experimentally for Mn3−xIr5B2+x and by DFT calculations for Mn2IrB2.

Magnetic and magnetoelectric properties of hybrid-frustrated Bi2Ir2−xMnxO7 pyrochlores

The present paper investigates the magnetic and magnetoelectric properties of Bi2Ir2−xMnxO7 compounds with respect to the degree of Mn doping denoted by x. It is found that the antiferromagnetic (AFM) interactions are initially enhanced with increasing x, but are then weakened with further increases in x. These findings are explained on the basis of the competition among AFM Ir–Ir, AFM Ir–Mn, and ferromagnetic Mn–Mn interactions. In addition, the electric transport properties at the temperature range studied present a metal-insulator transition in the range 0.05 ≤ x ≤ 0.15, while an insulating state occurs for x > 0.15 because of electron localization. At low temperatures, a small positive magnetoresistance (MR) effect is observed for x = 0, whereas a negative MR effect is observed for all Mn-doped samples. The 3d–5d electron interactions play a dominant role in determining the magnetic properties of the doped samples.

High-pressure structural stability of multiferroic hexagonalRMnO3(R=Y, Ho, Lu)

Structural changes in REMnO3 (RE= Y, Ho, Lu) under high pressure were examined by synchrotron x-ray diffraction methods at room temperature. Compression occurs more readily in the ab plane than along the c-axis. Under hydrostatic pressure (~11 GPa), the atoms hold their approximate ambient fractional positions in the unit cell and the spontaneous polarization shows no significant change. With increased pressure, a pressure-induced hexagonal to orthorhombic phase transition was observed starting at ~ 22GPa for Lu(Y)MnO3. A small volume fraction of Lu(Y)MnO3 is converted to the orthorhombic phase when the pressure is increased to 35 GPa and the orthorhombic phase is maintained on pressure release. High pressure IR absorption spectroscopy and Mn K-edge near edge x-ray absorption spectroscopy confirm that the hexagonal P63cm structure is stable below ~20 GPa and the environment around Mn ion is not changed. Shifts in the unoccupied p-band density of states with pressure are observed in the Mn K-Edge spectra. A schematic pressure-temperature phase diagram is given for the small ion REMnO3 system.

Exchange anisotropy pinning of a standing spin-wave mode

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was studied for a range of IrMn thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique `fingerprint' of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet/antiferromagnet interface anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region.

Strain sensor using stress-magnetoresistance effect of Ni–Fe/Mn–Ir exchange-coupled magnetic film

A strain sensor using a stress-magnetoresistance effect of a Ni–Fe/Mn–Ir exchange-coupled magnetic film was fabricated and evaluated. The stress magnetoresistance is used in the inverse magnetostrictive effect and the magnetoresistance effect in the magnetic film since an external stress is changed into an electric resistance in it. A compressive stress was measured by the strain sensor with a Mn–Ir (10 nm)/Ni–Fe (50 nm)/Ru (1 nm) exchange-coupled film. The change in resistivity Δρ/ρ is proportional to the applied compressive stress σ for σ≦50 MPa in the strain sensor. When increasing Ni–Fe layer thickness in the strain sensor, a gauge factor increased.

Thickness and annealing temperature dependences of magnetization reversal and domain structures in exchange biased Co/Ir–Mn bilayers

Domain structure and magnetization reversal process of exchange-coupled ferromagnet/antiferromagnet bilayers Co(x)/Ir–Mn(10 nm) were studied as a function of both thickness of the Co layer and annealing temperature. The exchange bias field of the thinnest film and the coercive field of the thicker films show monotonic increase at annealing temperature above 250 °C. In every case the bilayers are remagnetized by domain nucleation and domain wall motion. Domain size decreases rapidly for high annealing temperatures, while x-ray diffraction study indicated that the crystallographic texture did not change significantly. The observed features are discussed taking into account the magnetic structure at the interface and its evolution during annealing.

Spin configurations and interfacial diffusion in exchange bias and spin valve systems with Ir–Mn antiferromagnetic pinning layers

Exchange bias and spin valve structures with Fe as ferromagnetic layers selectively enriched in 57Fe and Ir–Mn of different compositions as antiferromagnetic pinning layers have been prepared by r.f. sputtering. Conversion Electron Mossbauer Spectroscopy and Magneto Optic Kerr Effect have shown that the local structure and interactions in the whole ferromagnetic layers, with direct influence on their magnetic reversal processes, depend on growing order of the layers and composition of the AF layer. Interfacial atomic diffusion is the main reason of perturbing the local structure of the ferromagnet. Mossbauer Spectroscopy is a powerfool tool which allows a detailed analysis of local configurations, in order to optimize the magnetic and giant magnetoresistive parameters of such multilayers of important technological applications.

Controlled rotation of the exchange-bias direction in IrMn∕Cu∕Co via ion irradiation

Co ∕ Cu ∕ Ir Mn films were irradiated with 40keV He+ ions varying the fluence and the current, with magnetic field applied at 120° with respect to the original exchange-bias direction. The angular variations of the exchange-bias field of the irradiated samples were compared with those of the as-made and the thermally annealed films. Gradual deviation of the exchange-bias direction with the fluence increase was observed. Complete reorientation of the easy axes of both ferromagnet and antiferromagnet toward that of the field applied during irradiation was achieved for fluences higher than 1×1015ions∕cm2, accompanied with a significant enhancement of the exchange-bias field.

Effect of Ir–Mn composition on exchange bias and thermal stability of spin valves with nano-oxide layers

The Ir–Mn bottom-pinned spin valves with nano-oxide layers (NOLs), Ta∕Ni81Fe19∕Ir–Mn∕Co90Fe10∕NOL∕Co90Fe10∕Cu∕Co90Fe10∕NOL∕Ta, were fabricated by dc magnetron sputtering. The magnetoresistance (MR), magnetization, and exchange bias have been studied as a function of Ir–Mn composition and annealing temperature. It was observed that the spin valves with the Ir–Mn layer containing relatively low Mn content (58.9–72.4at.% Mn) show the best thermal endurance. For these samples, the Mn diffusion is effectively hampered by the NOL with a large MR value of about 12.5% even after annealing at 300°C. On the other hand, the exchange bias field of the pinned CoFe layer shows a maximum at Mn content of about 72.4at.%, which is different from the widely adopted composition, Ir-80at.% Mn, optimized from the top-pinned NiFe∕Ir–Mn system. Moreover, the blocking temperature of the Ir–Mn∕CoFe system with 72.4at.% Mn is higher than that with 80.6at.% Mn. The present results suggest that the Ir–Mn∕CoFe pinning system with Mn content at about 72% renders the most favorable exchange bias and the best thermal stability for the bottom-pinned specular spin valves.

Uncompensated antiferromagnetic spins at the interface in Mn–Ir based exchange biased bilayers

The microscopic origin of the uncompensated antiferromagnetic (AFM) spins was investigated by means of the x-ray magnetic circular dichroism (XMCD) spectroscopy with transmission mode for Mn–Ir/ferromagnetic (FM) bilayers. As the AFM layer thickness increases, resonant absorption magnitude of Mn L edge naturally increases, but the XMCD magnitude does not change so much. When the FM layer material is modified, the XMCD signal of Mn L edge drastically changes not only in its magnitude but also in its sign. The XMCD signal vanishes without the FM layer. These facts clearly mean that the uncompensated Mn components are induced through the exchange interaction between the FM and the AFM layers and are localized at the very interface. Micromagnetic simulation within the framework of the classical Heisenberg model well supported the above conclusion.

Soft x-ray magnetic circular dichroism study of Mn–Ir∕Co–Fe bilayers with giant exchange anisotropy

Soft x-ray magnetic circular dichroism (XMCD) and element-specific magnetic hysteresis (ESMH) measurements were performed in transmission mode on Mn73Ir27 10nm∕Co70Fe30 2nm bilayers with different chemical orderings of the Mn–Ir layer.The unidirectional anisotropy constant was 0.55erg∕cm2 for the disordered Mn–Ir layer and 1.18erg∕cm2 for the ordered Mn–Ir layer. The XMCD signal of Mn was observed, which means the induced ferromagnetic component of Mn spins through the exchange coupling at the interface. No vertical offset of the Mn ESMH loops was observed for either the disordered or the ordered bilayers, which means that insignificant uncompensated Mn spin was pinned at the interface to induce exchange bias on the Co–Fe layer.

Transition between onion states and vortex states in exchange-coupled Ni–Fe∕Mn–Ir asymmetric ring dots

The transition between onion states and vortex states in exchange-coupled Ni–Fe∕Mn–Ir asymmetric ring dots has been investigated. A direction of domain wall motion, during the transition from the single-domain state to the vortex state via the onion state, depends on a sweep direction of an external field. This dependence fixes the directions of vortical magnetizations in the vortex states. The derivative of the amount of the domain wall motion with respect to the external field depends on the sweep direction of external field, and thus the hysteresis loop becomes asymmetric.

Mn – Ir ∕ Fe – Si exchange-coupled multilayer film with plural ferromagnetic resonance absorptions for wideband noise filter

Mn – Ir ∕ Fe – Si exchange-coupled multilayer films for a wideband and gigahertz band noise filters are fabricated and evaluated. The Fe–Si film has characteristics of high saturation magnetization of 19kG, low magnetostriction of the order of 10−6, and high resistivity of 73μΩcm. When the exchange bias magnetic field is introduced to the Fe–Si layers by the effect of Mn–Ir∕Fe–Si exchange-coupling, the ferromagnetic resonance (FMR) frequency of the multilayer film is higher than the natural frequency of the single Fe–Si film. In addition, the multilayer film which has different thicknesses in each Fe–Si layer has plural FMR frequencies. The multiple FMR frequency gives the film characteristic of wideband energy absorption. The FMR absorption bandwidth of the multilayer film which has three FMR frequencies is about three times wider than that of a single FMR film. Therefore, the multilayer film with plural FMR frequencies has an advantage in wideband noise absorption and will be a useful material for the wideband and gigahertz frequency range noise filterings.

L1 2 phase formation and giant exchange anisotropy in Mn 3Ir/Co–Fe bilayers

The degree of order S of Mn–Ir layers and the exchange anisotropy of Mn–Ir/Co–Fe bilayers were investigated for various chemical compositions of Mn–Ir layers, underlayer materials, and underlayer thicknesses. It was found that: (1) The compositional range over which L1 2-phase Mn 3Ir could be formed is 22–32 at% Ir and giant exchange anisotropy is obtained in this range. (2) Ru is favorable as an underlayer material for avoiding interdiffusion with the Mn–Ir layer during deposition on the temperature elevated substrate. (3) The underlayer thickness could be reduced to 5 nm while maintaining a giant exchange anisotropy in excess of 1 erg/cm 2.