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Unexpected Magnetic Moments in Manganese Doped CdSe 13 Nanoclusters Role of Ligands
No full textThis study explores the enhancement in magnetic and photoluminescence properties of Mn2 doped CdSe 13 nanoclusters, significantly influenced by the introduction of paramagnetic centers through doping, facilitated by optimized precursor chemistry and precisely controlled surface ligand interactions. Using a cost effective and scalable synthesis approach with elemental Se and NaBH4 Se NaBH4 in n octylamine, we tailored bonding configurations Cd amp; 8722;O, Cd amp; 8722;N, and Cd amp; 8722;Se on the surface of nanoclusters, as confirmed by EXAFS analysis. These bonding configurations allowed for tunable Mn2 doping with tetrahedral coordination, further stabilized by hydrogen bonded acetate ligands, as evidenced by 13C NMR and IR spectroscopy. Mulliken charge analysis indicates that the charge redistribution on Se2 amp; 8722; suggests electron transfer between surface ligands and the nanocluster, contributing to spin fluctuations. These tailored configurations markedly increased the nanoclusters amp; 8242; magnetic susceptibility and photoluminescence efficiency. The resulting nanoclusters demonstrated a clear concentration dependent response in emission lifetimes and intensities upon exposure to magnetic field effects MFE and spin spin coupling, alongside a large magnetic moment exceeding 40 amp; 956;B at 180 amp; 8197;K. These findings highlight the potential of these nanoclusters for magneto optical devices and spintronic applications, showcasing their tunable magnetic properties and exciton dynamic
Structural Modulation of Nanographenes Enabled by Defects, Size and Doping for Oxygen Reduction Reaction
No full textNanographenes are among the fastest growing materials used for the oxygen reduction reaction ORR thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal based electrocatalysts with functionalized graphene is highly desirable for reducing costs in energy conversion and storage systems. Generally, the enhanced ORR activity of the nanographenes is typically deemed to originate from the heteroatom doping effect, size effect, defects effect, and or their synergistic effect. All these factors can efficiently modify the charge distribution on the sp2 conjugated carbon framework, bringing about optimized intermediate adsorption and accelerated electron transfer steps during ORR. In this review, the fundamental chemical and physical properties of nanographenes are first discussed about ORR applications. Afterward, the role of doping, size, defects, and their combined influence in boosting nanographenes ORR performance is introduced. Finally, significant challenges and essential perspectives of nanographenes as advanced ORR electrocatalysts are highlighte
Thermal Activation and Deactivation of Ni Doped Ceria Catalysts in CO2 Methanation
Get PDFDiscovered almost 130 amp; 8201;years ago by P. Sabatier, CO2 hydrogenation to methane CO2 methanation is presently attracting attention as one of the most promising methods for storing intermittent renewable energy in the form of chemical fuels. Ni particles supported by CeO2 constitute a very effective, reliable, and reasonably priced catalyst for CO2 methanation. Recently a new type of CO2 methanation catalyst, consisting of cerium oxide ceria nanoparticles doped with nickel NiCeOx in a specific square planar configuration with an extremely high Ni mass specific activity and almost 100 CH4 selectivity, was reported. Here, a 50 enhancement in the CO2 conversion of the NiCeOx catalyst by carefully adjusting the calcination temperature is demonstrated. Notably, thermal aging at 600 amp; 8201; C enhances methanation performance by partially exsolving Ni to the surface, while higher temperatures 750 amp; 8201; C lead to larger Ni particles, increased CO production, and surface carbon deposition. Several in amp; 8201;situ and operando characterization methods are employed to correlate the thermal activation and deactivation of the catalyst with its nanoscale characteristics. Apart from their clear implications for the design of next generation Ni based CO2 methanation catalysts, these findings significantly enhance understanding of the complex interplay and nature of various surface sites involved in CO2 hydrogenatio
Oxidation states in manganese oxide clusters insights from oxygen evolving complex analogs
No full textThe Photosystem II complex is essential for the first stage of photosynthesis, facilitating dioxygen formation through the CaMn4O5 cluster, a key component of the oxygen evolving complex OEC . However, studying the S4 state, which is responsible for oxygen evolution, is challenging due to the transient nature and millisecond timescale of the S3 S4 S0 transition. Two competing models for the S4 state propose distinct oxidation states the oxo oxyl radical mechanism favors a high spin Mn IV oxyl species, while the oxo oxo coupling mechanism requires high spin Mn V oxo species. Neither Mn V oxo nor Mn IV oxyl species have been experimentally observed in polymanganese oxide clusters, including CaMn4O5. This thesis investigates whether high spin Mn V oxo or Mn IV oxyl species can be observed in cold gas phase cationic manganese oxide complexes, serving as subunits of the CaMn4O5 cluster. We explore both mononuclear and polymanganese oxide systems, using X ray absorption spectroscopy XAS and X ray magnetic circular dichroism to probe the oxidation states and spin properties. Computational methods, including multireference configuration interaction, density functional theory, and multiplet ligand field theory, were employed to support the experimental findings. Additionally, the influence of ligands, such as acetylacetone, on the oxidation states of manganese was studied. XAS results demonstrate that ligand coordination significantly affects the oxidation state, underscoring the importance of local symmetry in determining electronic properties. Overall, this work provides new insights into the electronic structure of manganese oxide clusters and their relevance to the OEC. The discovery of high spin Mn V species in polymanganese oxide complexes contributes to the understanding of the S4 state and may inform future studies on oxygen evolution in photosynthetic water splittin
Anomalous Hall Effect due to Magnetic Fluctuations in a Ferromagnetic Weyl Semimetal
Get PDFThe anomalous Hall effect AHE has emerged as a key indicator of time reversal symmetry breaking TRSB and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field free system becomes intricate in the presence of strong magnetic fluctuations. As a study case, we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE s topological origin. Through a combination of thermodynamic, transport, and muon spin relaxation measurements, we contrast the behavior below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results on PrAlGe provide general insights into the interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of kagome metals or certain transition metal dichalcogenide
Emergence of high mobility carriers in topological kagome bad metal Mn3Sn by intense photoexcitation
No full textKagome lattice materials offer novel playgrounds of exploring topologically nontrivial states of electrons under influence of many body interactions. A noncollinear kagome antiferromagnet M amp; 8290;n3 amp; 8290;Sn has attracted particular interest for application in spintronics owing to the large anomalous Hall effect related to the Weyl dispersion near the Fermi energy. In addition, strong electronic correlation suggesting the Kondo physics has also been implied. However, the effect of correlation on the band topology and their interplay remains elusive. Here, we investigate nonequilibrium Hall transport in a photoexcited M amp; 8290;n3 amp; 8290;Sn using time resolved terahertz Faraday rotation spectroscopy. In equilibrium, M amp; 8290;n3 amp; 8290;Sn is a bad metal close to the Mott Ioffe Regal limit with low carrier mobility, and thus only the anomalous Hall effect is discerned. By contrast, intense photoexcitation beyond an approximate threshold gives rise to a clear cyclotron resonance, namely the normal Hall effect, indicating the emergence of unusual carriers with 50 times lighter effective mass and 40 times less scattering. The lifetime of high mobility carriers as long as a few tens of picoseconds and a thresholdlike behavior for the pump fluence are hardly explained by contribution of photoexcited hot carriers. Instead, the emergence of unusual carriers may be accounted for by dielectric screening of the on site Coulomb interaction by high density delocalized photocarriers. A possible role of electronic correlation in equilibrium transport in M amp; 8290;n3 amp; 8290;Sn beyond the single particle picture is discusse
Fragile spin liquid in three dimensions
Get PDFMotivated by the recent appearance of the trillium lattice in the search for materials hosting spin liquids, we study the ground state of the classical Heisenberg model on its line graph, the trilline lattice.We find that this network realizes the recently proposed notion of a fragile spin liquid in three dimensions. Additionally, we analyze the Ising case and argue for a possible Z2 quantum spin liquid phase in the corresponding quantum dimer model. Like the well known U 1 spin liquids, the classical phase hosts moment fractionalization evidenced by the diluted lattice, but unlike those, it exhibits exponential decay in both spin correlations and interactions between fractionalized moments. This provides an instance of a purely short range correlated classical Heisenberg spin liquid in three dimension
Anisotropy driven spin reorientation, and two step magnetic ordering in cubic semiconducting spinel Cr0.1Mn0.9Fe0.2Co1.8O4
No full textThe nature of magnetism in the cubic spinel is reported based on systematic investigations by means of magnetization M , ac susceptibility amp; 967; and heat capacity Cp measurements, as well as by neutron diffraction. Structural characterization of the sample was done using x ray absorption spectroscopy, neutron and synchrotron diffraction. The M vs. T variation in different magnetic fields indicate ferrimagnetic ordering below TC 230 K, followed by a magnetic field and anisotropy induced spin reorientation at TSR 150 K. With increasing T starting from 2 K, the coercivity and anisotropy field HK decrease and become negligible for T gt; TSR. A model to explain the HC vs. T data shows that TSR is due to reorientation of M along H when H gt; HK. The CP vs. T data shows a weak lambda type anomaly at TC with changes in magnetic entropy smaller than those observed below TSR suggesting that long range magnetic ordering is completed below TSR. For TSR lt; T lt; TC, the presence of weakly interacting magnetic clusters having weak short range interactions is evident based on analysis of magnetization and ac susceptibilities. Exchange constants JAA 7.9 K, JAB kB 22.6 K and JBB kB 5.3 K are determined from the temperature dependence of paramagnetic susceptibility for T gt; TC . This analysis also shows the low spin S 0 state of Co3 ions on the B sites which along with negligible HK for TSR lt; T lt; TC produces weakly interacting magnetic clusters in this magnetic semiconductor with bandgap 0.57 e
Anisotropy Dependent Decay of Room Temperature Metastable Skyrmions and a Nascent Double q Spin Texture in Co8Zn9Mn3
No full textChiral cubic Co Zn Mn magnets exhibit diverse topological spin textures, including room temperature skyrmion phases and robust far from equilibrium metastable states. Despite recent advances in understanding metastable skyrmions, the interplay between compositional disorder and varying magnetic anisotropy on the stability and decay of metastable textures, particularly near room temperature, remains incompletely understood. In this work, the equilibrium and metastable skyrmion formation in Co8Zn9Mn3 is examined, revealing transformations between distinct metastable spin textures induced by temperature and magnetic field. At room temperature, the decay dynamics of metastable skyrmions exhibits a strong dependence on magnetic anisotropy, showcasing a route towards tailoring relaxation behavior. Furthermore, a nascent double q spin texture, characterized by two coexisting magnetic modulation vectors q, is identified as a minority phase alongside the conventional triple q hexagonal skyrmion lattice. This double q texture can be quenched as a metastable state, suggesting both its topological character, and its role as a potential intermediary of metastable skyrmion decay. These findings provide new insights into the tunability of equilibrium and metastable topological spin textures via chemical composition and magnetic anisotropy, offering strategies for designing materials with customizable and dynamic skyrmion properties for advanced technological application
Understanding molecular confinement in polymeric nanoporous materials via infrared spectroscopic measurements
No full textThe existence of molecular confinement in nanoporous polymeric samples is a discussion with notable impact that has been opened in the past decade. This work aims to shed more light on the topic and demonstrate molecular confinement with an additional analytical method. For this purpose, nanoporous polymeric samples were prepared out of PMMA from different commercial grades and foamed via gas dissolution foaming. The molecular confinement in these samples is demonstrated by using Attenuated Total Reflectance ATR FTIR spectroscopy in microscopic mode and following the changes in both spectral peak areas and peak shifts with changes in the pore wall thickness. Utilizing its high precision, the shortening of bond lengths due to confinement is evaluated via peak shifts. ATR is compared to previous functional techniques, namely Raman spectroscopy and DSC. The results prove ATR effective in both cases, and reveal that confinement causes changes in the polymeric chains within pore walls with thicknesses of less than 100 amp; 119899; amp; 119898;. For these cases, ATR and Raman spectroscopy demonstrate that shortening of atomic bond lengths affects molecules polarizability and causes overall chain immobilizatio