Mn 3s Research Articles

Effects of Co for Mn substitution on the electronic properties of Mn2-xCoxVAl as probed by XPS

Detailed theoretical and experimental investigations on the electronic and magnetic properties of the Heusler compounds Mn2-xCoxVAl with L21 structure are presented. The samples have been examined by X-ray diffraction, magnetization measurements and X-ray photoemission. The magnetic measurements show that the Curie temperatures decrease with Co content, ranging between 771 K (x = 0) and 289 K (x = 1), while the magnetization of the samples follows the Slater-Pauling rule.Additionally, electronic band structure calculations using the Korringa-Kohn-Rostoker (KKR) Greens function method have been performed. The evolution of the half-metallic character with the Co content x in the Mn2-xCoxVAl alloys is discussed based on the density of states (DOS) calculations. The influence of the Co doping on the individual magnetic moments of the Mn and V has been evidenced. Also, the small individual spin moments of Mn and V determined by theoretical calculations in MnCoVAl (x = 1) are confirmed by the Mn 3s and V 3s core level analysis of the X-ray photoemission spectroscopy investigations.

Charge transfer effect for the La0.7Ca0.3MnO3/NiO heterostructure and novel interfacial ferromagnetism

We report the formation of new ferromagnetic (FM) states in antiferromagnetic (AFM) NiO at the interface with FM La0.7Ca0.3MnO3 (LCMO). The LCMO/NiO heterostructures exhibit an exchange bias field of 209Oe that vanishes as the temperature rises above 90K. A new magnetization temperature at 90K is observed and can be ascribed to Ni3+-O-Mn3+ superexchange interactions. Mn 3s and Ni 3p core-level spectra, measured by X-ray photoelectron spectroscopy, show a direct evidence of charge transfer effects of the type Mn4+-Ni2+→Mn3+-Ni3+ at the interface region. The valence band offset (VBO) at the LCMO/NiO interface can be determined to be ΔEVBO∼0.77eV. The valence band of LCMO is shifted to higher binding energy compared with NiO. Thus, charge transfer occurred because of the shifting of the valence band edge at the heterostructure interfaces. We speculate that the superexchange interactions of the Ni3+ and Mn3+ at the interface give rise to the novel low-temperature FM order and the magnetic regions that pin the FM LCMO layer as the temperature decreases.

Valence state of Mn in La<sub>1−<i>x</i></sub>Sr<sub><i>x</i></sub>MnO<sub>3</sub> probed by resonant Mn 3<i>s</i>→2<i>p</i> x-ray emission spectroscopy

Valence state of Mn in La<sub>1−<i>x</i></sub>Sr<sub><i>x</i></sub>MnO<sub>3</sub> probed by resonant Mn 3<i>s</i>→2<i>p</i> x-ray emission spectroscopy

Biomimetic Mn-Catalases Based on Dimeric Manganese Complexes in Mesoporous Silica for Potential Antioxidant Agent.

Two new structural and functional models of the Mn-catalase with formula [{Mn(III)(bpy)(H2O)}(μ-2-MeOC6H4CO2)2(μ-O){Mn(III)(bpy)(X)}]X, where X = NO3 (1) and ClO4 (2) and bpy = 2,2'-bipyridine, were synthesized and characterized by X-ray diffraction. In both cases, a water molecule and an X ion occupy the monodentate positions. The magnetic properties of these compounds reveal a weak antiferromagnetic behavior (2J = -2.2 cm(-1) for 1 and -0.7 cm(-1) for 2, using the spin Hamiltonian H = -2J S1·S2) and negative zero-field splitting parameter DMn (-4.6 cm(-1) and -3.0 cm(-1) for 1 and 2, respectively). This fact, together with the nearly orthogonal orientation of the Jahn-Teller axes of the Mn(III) ions explain the unusual shape of χMT versus T plot at low temperature. Compound 1 presents a better catalase activity than 2 in CH3CN-H2O media, probably due to a beneficial interaction of the NO3(-) ion with the Mn complex in solution. These compounds were successfully inserted inside two-dimensional hexagonal mesoporous silica (MCM-41 type) leading to the same hybrid material ([Mn2O]@SiO2), without the X group. The manganese complex occupies approximately half of the available pore volume, keeping the silica's hexagonal array intact. Magnetic measurements of [Mn2O]@SiO2 suggest that most of the dinuclear unit is preserved, as a non-negligible interaction between Mn ions is still observed. The X-ray photoelectron spectroscopy analysis of the Mn 3s peak confirms that Mn remains as Mn(III) inside the silica. The catalase activity study of material [Mn2O]@SiO2 reveals that the complex is more active inside the porous silica, probably due to the surface silanolate groups of the pore wall. Moreover, the new material shows catalase activity in water media, while the coordination compounds are not active.

Ferroelectric capped magnetization in multiferroic PZT/LSMO tunnel junctions

Self-poled ultra-thin ferroelectric PbZr0.52Ti0.48O3 (PZT) (5 and 7 nm) films have been grown by pulsed laser deposition technique on ferromagnetic La0.67Sr0.33MnO3 (LSMO) (30 nm) to check the effect of polar capping on magnetization for ferroelectric tunnel junction devices. PZT/LSMO heterostructures with thick polar PZT (7 nm) capping show nearly 100% enhancement in magnetization compared with thin polar PZT (5 nm) films, probably due to excess hole transfer from the ferroelectric to the ferromagnetic layers. Core-level x-ray photoelectron spectroscopy studies revealed the presence of larger Mn 3s exchange splitting and higher Mn3+/Mn4+ ion ratio in the LSMO with 7 nm polar capping.

Magnetic properties and magnetocaloric effect in La0.7Sr0.3−xBixMnO3 manganites

Structural properties, magnetization and magnetocaloric effect measurements in the compounds based on lanthanum–strontium–bismuth manganites La0.7Sr0.3−xBixMnO3 (LSBiMO) with 0.05⩽x⩽0.30 have been performed. The valence states of elements entering into the composition of investigated LSBiMO samples were analyzed for x=0.15 and 0.3 using the HR XPS spectra of Bi 4f, La 3d, Mn 3s and Sr 3d. According to X-ray powder diffraction data the crystalline structure of the samples is perovskite-like with a small rhombohedral distortion. The a and c lattice parameters and unit cell volume V are established to increase with increasing Bi content. All the manganites show ferromagnetic-like ordering with second order phase transition to paramagnetic state. The Curie temperature and magnetization decrease at substitution of Sr2+ for Bi3+ ions. The magnetic entropy changes were calculated using the field dependence of isothermal magnetization in the terms of the thermodynamic Maxwell relation. The maximum magnetic entropy change value was shown to be 0.94Jkg−1K−1 for x=0.05 for a field change of 1T.

Enlarged Mn 3s splitting and room-temperature ferromagnetism in epitaxially grown oxygen doped Mn2N0.86 films

Single-phase and oxygen doped Mn2N0.86 thin films have been grown on MgO (111) by plasma-assisted molecular beam epitaxy. The films grow under tensile strain and, remarkably, they show ferromagnetic-like interactions at low temperature and ferromagnetic ordering agreed well with the Bloch-law T3/2 at room-temperature. We further demonstrate the enlarged Mn 3s splitting (6.46 eV) and its possible relation to the observed ferromagnetism. Our study not only provide a strategy for further theoretical work on oxygen doped manganese nitrides, but also shed promising light on utilizing its room-temperature FM property to fabricate spintronic devices.

Inverse photoemission and photoemission spectroscopic studies on sputter-annealed Ni–Mn–Sn and Ni–Mn–In surfaces

The electronic structure of nearly stoichiometric Ni–Mn–Sn and Ni–Mn–In surface is investigated by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated inverse photoemission spectra shows that the dominant feature is related to Mn 3d-like states. The overall shape and peak position of the theoretically obtained spectra show good agreement with the experimental ultraviolet photoemission valence band spectra. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3d and Mn 3d band hybridization. Both inverse photoemission and ultraviolet photoemission study show a rigid band shift between Ni2MnIn and Ni2MnSn because of band filling, due to increase in the number of 5p electrons from In to Sn. Mn 2p and 3s core-level reveal unambiguous existence of exchange splitting in both the materials.

The Mn2+/Mn3+ state of La0.7Ce0.3MnO3 by oxygen reduction and photodoping

Films of cerium-doped LaMnO3, which has been intensively discussed as an electron-doped counterpart to hole-doped mixed-valence lanthanum manganites during the past decade, were analyzed by x-ray photoemission spectroscopy with respect to their manganese valence under photoexcitation. The comparative analysis of the Mn 3s exchange splitting of La0.7Ce0.3MnO3 (LCeMO) films in the dark and under illumination clearly shows that both oxygen reduction and illumination are able to decrease the Mn valence towards a mixed 2+/3+ state, independently of the film thickness and the degree of CeO2 segregation. Charge-injection from the photoconductive SrTiO3 substrate into the Mn eg band with carrier lifetimes in the range of tens of seconds and intrinsic generation of electron–hole pairs within the films are discussed as two possible sources of the Mn valence shift and the subsequent electron doping.

Manganese oxide thin films prepared by pulsed laser deposition for thin film microbatteries

Manganese oxide thin films with various oxidation states (MnO, Mn3O4 and Mn2O3) have been prepared by pulsed laser deposition using a Mn target at different oxygen partial pressures. The structural and morphological features of the as-deposited thin films are characterized by X-ray diffraction, Raman, field emission scanning electron microscopy (FESEM). The oxidation states of Mn in different thin films are investigated by X-ray photoelectron spectroscopy for both Mn 2p and 3s levels. It is found that the structure, surface morphology, and Mn oxidation state of the thin films can be tuned by oxygen partial pressure during the deposition. As anode for thin film lithium-ion microbatteries, the Mn3O4 thin film electrode exhibits the largest reversible capacity up to 800 mAh g−1 with good cycling stability and excellent rate capability. The promising electrochemical performance of the Mn3O4 thin film electrode indicates the potential application of Mn3O4 thin film anode in all solid-state thin film microbatteries.

Effects of substitution of Pr, Nd, and Sm for La on the magnetic properties and magnetocaloric effect of La1.4Ca1.6Mn2O7

The effects of Pr, Nd and Sm partial substitution for La on the magnetic properties and magnetocaloric effect near the critical phase transition temperatures of La1.4Ca1.6Mn2O7 are analyzed. Polycrystalline powders of La1.2R0.2Ca1.6Mn2O7 double layered manganites (R=La, Pr, Nd, Sm) with grain sizes of 20–30nm were successfully synthesized by a sol–gel method. The substitution of Pr, Nd and Sm for La ions increases the inter-layer lattice distortion, leading to a decrease of the exchange interaction strength. The magnetic measurements evidence a spin-glass-like behavior at low temperatures for all samples, which may be due to frustration of random competing ferromagnetic and antiferromagnetic interactions together with the anisotropy originating from the layered structure. The Mn 3s XPS spectra show an exchange splitting around 4.75eV from which the Mn formal valence is estimated to be around 3.65+, in excellent agreement with the magnetic data obtained at temperatures above the room temperature. A moderate magnetocaloric effect is found for all samples, with the maximum entropy change located at temperatures near the magnetic transition ones. The high RCP(S) values together with the broadened magnetic entropy curves and low magnetic hysteresis suggest the possibility to use these materials for magnetic refrigeration devices.

Valence state of the manganese ions in mixed-valence La1−αBiβMn1+δO3±γ ceramics by Mn 2p and Mn 3s X-ray photoelectron spectra

Valence state of Mn in La1−αBiβMn1+δO3±γ (LBMO) ceramic samples and in orthorhombic manganates RMn2O5 (R=Y, Bi, Eu, Gd), is studied using Mn 2p- and Mn 3s-spectra. Both Mn3+ and Mn4+ ions are shown to be present in those compounds. Relative Mn3+/Mn4+ ions contents are determined by fitting experimental Mn 2p-spectra with weighted superpositions of theoretical spectra of Mn3+ and Mn4+ ions calculated in one-configuration Pauli–Fock approximation considering thermal excitations in initial state. Content of the Mn4+ ions correlates with the deviation δ in La1−αBiβMn1+δO3±γ from stoichiometry, La1−xBixMnO3. Separation of low-spin and high-spin components of Mn 3s-spectrum can be sensible to the relative content of Mn3+ and Mn4+ ions. Mn3+/Mn4+ ratios derived from Mn 2p- and from Mn 3s-spectra compare well in the case of the RMn2O5 manganates, while in the case of the LBMO ceramics the results obtained from the Mn 3s spectra are physically meaningless. Due to a complex interplay between 3d-electrons delocalization and strong many-electron effects the 3s spectra of 3d-elements may be misleading.

Application of 3s X-Ray Photoelectron Spectra for Determination of Charge States and Magnetic Moments of 3d Ions in Oxides

There are presented core-level 3s X-ray photoelectron spectra of some 3d oxides. The possibility to extract additional information on intra- and interatomic exchange effects from 3s X-ray photoelectron spectra is demonstrated. The results pointed to the possibility of using X-ray photoelectron 3s spectra for estimation of local spin magnetic moments localized on 3d elements in manganese and iron oxides. We have found that for doped manganites, the Mn formal valency from 3+ to 3.3+ is not accompanied by any decrease in the Mn 3s splitting. This fact can be explained by the holes in the O 2p states (d4L ground-state configuration). For Cu, Ni, and Co oxides, the charge-transfer effect dominates the multiplet effect in the 3s spectra which allows to estimate the occupancy of 3d states.

Use of XPS to Identify the Oxidation State of Mn in Solid Surfaces of Filtration Media Oxide Samples from Drinking Water Treatment Plants

X-ray photoelectron spectroscopy (XPS) was used to identify Mn(II), Mn(III), and Mn(IV) in the surfaces of pure oxide standards and filtration media samples from drinking water treatment plants through the determination of the magnitude of the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line. The Mn 3p region has been widely studied by applied physicists and surface scientists, but its application to identify the oxidation state of Mn in heterogeneous oxide samples has been limited. This study shows that the use of both the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line provides a feasible means of determining the oxidation state of manganese in complex heterogeneous, environmentally important samples. Surface analysis of filtration media samples from several drinking water treatment plants was conducted. While Mn(IV) was predominant in most samples, a mixture of Mn(III) and Mn(IV) was also identified in some of the filtration media samples studied. The predominance of Mn(IV) in the media samples was felt to be related to the maintenance of free chlorine (HOCl) at substantial concentrations (2-5 mg*L(-1) as Cl2) across these filters. XPS could be a useful tool to further understand the specific mechanisms affecting soluble Mn removal using MnOx-coated filtration media.

Characterization of The Lithium−Manganese Ferrite LiFeMnO4 Prepared by Two Different Methods

Lithium−manganese ferrite LiFeMnO4 was prepared using two different methods: a conventional ceramic high-temperature solid-state reaction technique (Cer) and thermal decomposition of metal nitrate salts (NTD). The characterization of the compounds was carried out by SEM/EDX, XRD, XPS, Fe K- and Mn K-edge XANES, and Mossbauer spectroscopy. Both Cer and NTD LiFeMnO4 samples have the nominal expected Fe/Mn atomic ratio and show a homogeneous morphology, but they exhibit different particle sizes. Fe K-edge XANES and Mossbauer spectroscopy results show that the oxidation state of Fe ions is +3 in both samples, whereas the Mn K-edge XANES data indicate that the bulk average Mn oxidation state is +3 for the NTD sample and close to +4 for the Cer one. Thus, to maintain the charge neutrality, the NTD sample has to be nonstoichiometric in oxygen with a composition close to LiFeMnO3.5. The Mn 3s XPS data indicate that the average surface oxidation state of Mn is also lower in the NTD sample. The results suggest the ...

Synthesis, molecular and crystalline architectures, and properties of novel bis(bidentate) and bis(tridentate) Schiff base bridged dinuclear mercury(II)pseudohalides: Control of coordination numbers by varying denticities

A tetracoordinated [Hg 2(L 1)(SCN) 4] ( 1) [L 1 = N,N′-(bis-(pyridin-2-yl)benzylidene)-1,2-ethanediamine] and two pentacoordinated [Hg 2(L 2)(X) 4] [L 2 = N-((1-pyridin-2-yl)formylidene)-N′-[2-(4-{2-[((1-pyridin-2-yl)formylidene) amino]ethyl}piperazin-1-yl)ethyl]amine; X = N 3 - , ( 2) and X = NCS −, ( 3)] dinuclear mercury(II) compounds have been prepared and characterized using microanalytical, spectroscopic, thermal and X-ray crystallographic results. Structural analyses reveal bis(bidentate) congregation behaviour of classical tetradentate L 1 and bis(tridentate) character of L 2 encapsulating two metal centers. Each mercury(II) center in 1 is in a distorted tetrahedral coordination environment with HgN 2S 2 chromophore. Hg(1) is attached with two N atoms of L 1 and two S atoms of two terminal thiocyanates whereas neighbouring Hg(1) is ligated to the other two N donor set of the same Schiff base completing its bis(bidentate) mode and two S atoms of thiocyanates. In 2 and 3 each mercury(II) center adopts a distorted square pyramidal geometry with MN 5 (in 2) and MN 3S 2 (in 3) chromophores and two metal(II) centers are encapsulated by bis(tridentate) congregation behaviour of L 2 through donation of three N donor set to each metal and the fourth and fifth positions are occupied by two N atoms of terminal azides in 2 and two S atoms of terminal thiocyanates in 3. In solid-state, dinuclear units of 1 pack through cooperative C–H⋯N and C–H⋯S hydrogen bonds and C–H⋯π interactions giving rise to a 3D network. Individual dinuclear units of 2 and 3 self-assemble through cooperative C–H⋯N hydrogen bondings and C–H⋯π interactions affording 3D network structure and 2D continuum, respectively. In DMF solutions at room temperature all the complexes display high-energy intraligand 1(π–π∗) fluorescence.

Charge state of manganese ions and the nonstoichiometry of Ca1 − x La y MnO3 − δ single crystals

The charge states and effective spins of manganese ions in nonstoichiometric single crystals of Ca1 − x La y MnO3 − δ (x = 0, 0.05, 1) manganites have been determined from the exchange splitting of Mn 3s X-ray photoelectron spectra. The chemical composition of the manganite samples under investigation, including the concentration of oxygen, has been determined using the data of the X-ray microanalysis of cations. It has been found that the manganite single crystals under investigation have large defectiveness in both the cation and oxygen sublattices. The efficiency of the complex use of 3s photoelectron spectroscopy and X-ray microanalysis in the determination of the charge state of manganese ions and violations of stoichiometry in doped and defected manganites has been demonstrated.

X-ray diffraction and photoelectron spectroscopy study of swift heavy ion irradiated Mn/p-Si structure

The electronic structure and interfacial chemistry of thin manganese films on p-Si (1 0 0) have been studied by photoelectron spectroscopy measurements using synchrotron radiation of 134 eV and from X-ray diffraction data. The Mn/p-Si structures have been irradiated from swift heavy ions (∼100 MeV) of Fe 7+ with a fluence of 1 × 10 14 ions/cm 2. Evolution of valence band spectrum with a sharp Fermi edge has been obtained. The observed Mn 3d peak has been related to the bonding of Mn 3d–Si 3sp states. Mn 3p (46.4 eV), Mn 3s (81.4 eV) and Si 2p (99.5 eV) core levels have also been observed which show a binding energy shift towards lower side as compared to their corresponding elemental values. From the photoelectron spectroscopic and X-ray diffraction results, Mn 5Si 3 metallic phase of manganese silicide has been found. The silicide phase has been found to grow on the irradiation.

Electronic properties of LiMn2−x Ti x O4

Ti-substituted LiMn2O4 (LiMn2−x Ti x O4, x=0, 0.15, 0.30, 0.45, 0.60, and 0.75) has been synthesized using solid-state reactions. Their crystal and electronic structures were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). XRD data suggested that the lattice parameters of LiMn2−x Ti x O4 increase due to the replacement of Mn by Ti ions. XPS results indicated that the substituted Ti ions were in +4 oxidation state; consequently, the normal oxidation state of Mn ions has been detected by measuring the binding energy splitting of Mn 3s states, which decreases with the content of substituted Ti. The valence band spectra suggested that the intensity of e g level of Mn 3d orbitals increased due to the increase of the Mn3+/Mn4+ ratio.

Manganese adlayers on i-Al–Pd–Mn quasicrystal: growth and electronic structure

Pseudomorphic growth of thin elemental metal films is often observed on a variety ofcrystalline solids. On quasicrystalline surfaces with their complex structure and the absenceof translational periodicity, the situation is different since elemental metals do not exhibitquasicrystalline order, and hence the specific interaction between overlayer and substrate isdecisive. Here we study the growth of manganese films on an icosahedral i-Al–Pd–Mn alloywith a view to establishing the growth mode and electronic structure. Although weobserve an exponential intensity variation of the adlayer and substrate related x-rayphotoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED)shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure ofthe Mn 2p core level line reveals considerable electronic structure differencesbetween the quasicrystalline and elemental metal environment. Evidence of asubstantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 µB) is obtained from the Mn 3s exchange splitting.