Mn Layers Research Articles

Patterned nano-domains in PMN-PT single crystals

The domain structure, dielectric, and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals with nanocomposite electrode, which includes MnOx semiconductor nanogratings and a Ti/Au conductive layer, were studied in this paper. These artificial MnOx nanogratings can alter the electric field distribution and then enhance the domain density. PMN-PT crystals with Ti/Au-MnOx nanocomposite electrodes showed high piezoelectric constant of 2250 p.m./V and dielectric constant of 5400 at 1 kHz, respectively. Compared to ones with conventional planar electrodes, the piezoelectric and dielectric constants of the samples with nanocomposite electrodes were increased 36.7% and 38.3%, respectively. Piezoresponse force microscopy (PFM) images revealed the domain pattern near the electrode/single crystal interface. A linear domain structure induced by the MnOx nanocomposite electrode was found in the samples with thickness less than 200 μm. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) results showed the diffusion of Mn about 300 nm in depth in PMNPT crystal after heat treatment during MnOx nanocomposite electrode. It is believed that the localized high electric fields induced by fringe effects caused by the nanocomposite electrode can enhance nucleation of new domains, and that diffusion from the patterned Mn layer may also lead to an enhancement in domain wall mobility. Our findings open up a new domain engineering technique for tailoring the dielectric and piezoelectric properties of PMN-PT single crystals.

Magnetic and structural properties of RTA-processed L10 FePt-Mn thin films

In this study, we have investigated the effect of Mn addition on texture, phase formation, and magnetic properties of L10 FePt thin films. FePt/Mn/FePt trilayers were processed by rapid thermal annealing in the temperature range of 650 – 800°C for 30 s in N2 atmosphere. It is shown that Mn addition up to 10 at.% supports L10(001)-texture formation resulting in large perpendicular magnetic anisotropy. However, it is observed that Mn is only partially incorporated into the FePt lattice. It was found that Mn diffuses through the FePt top layer to the sample surface, promoting the ordering process and forming a Mn oxide layer.

Overview of the Oxygen Behavior in the Degradation of Li2MnO3 Cathode Material

The Li2MnO3 cathode material is vulnerable to complex degradation behaviors during the operation of battery although it has attracted much attention recently due to its potentially large capacity. In this study, we comprehensively examined the degradation process in Li2MnO3, using theoretical density functional computations as well as experimental techniques (in situ X-ray absorption near edge structure spectroscopy, X-ray diffraction, and Raman spectroscopy). Our study reveals that during the delithiation process, the Li ions mixed in the Mn layer are removed together with those in the Li layer, thereby inducing the release of oxygen atoms. The oxygen loss reaction is energetically favorable at the highly delithiated states, and it can reduce the plateau voltage in the charging curve. Such oxygen loss was observed during or even before the second cycle and furthermore it accelerates the phase transformation of the layered structure to a spinel one. Our results also suggest that oxygen release can be prev...

Atomically Resolved Short-Range Order at the Nanoscale in the Ca-Mn-O System.

The elucidation of the reaction mechanisms involving redox processes in functional transition-metal oxides, which usually start in areas of very few nanometers in size, is yet a challenge to be satisfactorily achieved. Atomically resolved HAADF and EELS have provided both chemical and structural information at the nanoscale, which reveal the preservation of short-range cationic order in areas of 2-3 nm length as the driving force behind the reversibility of the Ca2Mn3O8-Ca2Mn3O5 redox process. Oxygen evolution is accommodated by cationic diffusion along the Ca and Mn layers of the cation-deficient Ca2Mn3O8 delafossite related structure, whereas Mn remains octahedrally coordinated.

On the delta-type doping of GaAs-based heterostructures with manganese compounds

Heterostructures, which incorporate GaAs/InGaAs/GaAs quantum wells and are doped with spatially remote monatomic Mn layers, are formed on GaAs(001) substrate under conditions of multilayer buildup by the method of molecular-beam epitaxy. Combined studies of the obtained samples were performed by the method of secondary-ion mass spectrometry, by measurements of X-ray diffraction, and using a transmission electron microscope. The heterostructures under study with a doping impurity concentration amounting to 0.5 single layers are elastically stressed and demonstrate planar clearly defined interfaces without visible extended or point defects. A method for visualization of the distribution of the manganese concentration in the three-dimensional GaAs matrix in the vicinity of a quantum well is suggested. According to experimental results, there is a probability for manganese diffusion into the GaAs/InGaAs/GaAs quantum well when the critical thickness of the GaAs buffer layer is decreased to a value smaller than 3 nm.

Transition metal partially supported graphene: Magnetism and oscillatory electrostatic potentials

Using first-principles calculations, we show that Mn and Cr layers under graphene exhibit almost zero magnetic moment due to anti-ferromagnetic order, while ferromagnetic coupling in Fe, Co, and Ni leads to large magnetic moment. Transition metal partially supported graphene, with a mixture of supported and pristine areas, exhibits an oscillatory electrostatic potential, thus alternating the electric field across the supported and pristine areas. Such an effect can be utilized to control mass transport and nanostructure self-organization on graphene at the atomic level.

Perpendicular magnetic anisotropy in ZnMnS ultra-thin films caused by structural cleavage

Half tetragonal ZnMnS crystal based on three single layers of Zn, S and Mn was investigated by including spin–orbit coupling in full potential linearized augmented plane waves method. We show that the magnetic anisotropy exhibits a strong dependence with structural cleavage, which induces an out-of plane magnetic easy axis. The perpendicular magnetic anisotropy was calculated to be 1890.9µeV. The anti-ferromagnetic behavior is displayed between Mn atoms having a magnetic moment of ±3.57μB with c(2×2) magnetic configuration. The results indicate that ZnMnS compound has interesting optical and magnetic properties for spintronics applications.

First Principles Study of Adsorption of Hydrogen on Typical Alloying Elements and Inclusions in Molten 2219 Al Alloy.

To better understand the effect of the components of molten 2219 Al alloy on the hydrogen content dissolved in it, the H adsorption on various positions of alloying element clusters of Cu, Mn and Al, as well as the inclusion of Al2O3, MgO and Al4C3, were investigated by means of first principles calculation, and the thermodynamic stability of H adsorbed on each possible site was also studied on the basis of formation energy. Results show that the interaction between Al, MgO, Al4C3 and H atoms is mainly repulsive and energetically unfavorable; a favorable interaction between Cu, Mn, Al2O3 and H atoms was determined, with H being more likely to be adsorbed on the top of the third atomic layer of Cu(111), the second atomic layer of Mn(111), and the O atom in the third atomic layer of Al2O3, compared with other sites. It was found that alloying elements Cu and Mn and including Al2O3 may increase the hydrogen adsorption in the molten 2219 Al alloy with Al2O3 being the most sensitive component in this regard.

Topochemical Reduction of YMnO3 into a Composite Structure.

Topochemical modification methods for solids have shown great potential in generating metastable structures inaccessible through classical synthetic routes. Here, we present the enhanced topotactic reduction of the multiferroic compound YMnO3. At moderate temperature in ammonia flow, the most reduced YMnO3-δ (δ = 0.5) phase could be stabilized. XRD, PND, and HREM results show that phase separation occurs into two intimately intergrown layered sublattices with nominal compositions ∞[YMn2+O2+x](1-2x)+ and ∞[YMn2+O3-x](1-2x)- containing versatile Mn2+ coordinations. The former sublattice shows original AA stacking between Mn layers, while AB stacking in the latter results from oxygen removal from the parent YMnO3 crystal structure.

Interfacial Charge Engineering in Ferroelectric-Controlled Mott Transistors.

Heteroepitaxial coupling at complex oxide interfaces presents a powerful tool for engineering the charge degree of freedom in strongly correlated materials, which can be utilized to achieve tailored functionalities that are inaccessible in the bulk form. Here, the charge-transfer effect between two strongly correlated oxides, Sm0.5 Nd0.5 NiO3 (SNNO) and La0.67 Sr0.33 MnO3 (LSMO), is exploited to realize a giant enhancement of the ferroelectric field effect in a prototype Mott field-effect transistor. By switching the polarization field of a ferroelectric Pb(Zr,Ti)O3 (PZT) gate, nonvolatile resistance modulation in the Mott transistors with single-layer SNNO and bilayer SNNO/LSMO channels is induced. For the same channel thickness, the bilayer channels exhibit up to two orders of magnitude higher resistance-switching ratio at 300 K, which is attributed to the intricate interplay between the charge screening at the PZT/SNNO interface and the charge transfer at the SNNO/LSMO interface. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy studies of SNNO/LSMO heterostructures reveal about 0.1 electron per 2D unit cell transferred between the interfacial Mn and Ni layers, which is corroborated by first-principles density functional theory calculations. The study points to an effective strategy to design functional complex oxide interfaces for developing high-performance nanoelectronic and spintronic applications.

Evidence for self-organized formation of logarithmic spirals during explosive crystallization of amorphous Ge:Mn layers

Logarithmic spirals are found on different length scales in nature, e.g., in nautilus shells, cyclones, and galaxies. The underlying formation laws can be related to different growth mechanisms, pressure gradients, and density waves. Here, we report on the self-organized formation of symmetric logarithmic crystallization spirals in a solid material on the micrometer length scale, namely, in an amorphous Ge:Mn layer on a Ge substrate. After exposure to a single light pulse of a flashlamp array, the Ge:Mn layer is crystallized and reveals a partially rippled surface and logarithmic microspirals. Finally, we present a model describing the formation of the crystallization spirals by directional explosive crystallization of the amorphous Ge:Mn layer, which is triggered by the flashlamp light pulse.

P2 Orthorhombic Na0.7[Mn1-xLix]O2+y as Cathode Materials for Na-Ion Batteries.

P2-type manganese-based oxide materials have received attention as promising cathode materials for sodium ion batteries because of their low cost and high capacity, but their reaction and failure mechanisms are not yet fully understood. In this study, the reaction and failure mechanisms of β-Na0.7[Mn1-xLix]O2+y (x = 0.02, 0.04, 0.07, and 0.25), α-Na0.7MnO2+y, and β-Na0.7MnO2+z are compared to clarify the dominant factors influencing their electrochemical performances. Using a quenching process with various amounts of a Li dopant, the Mn oxidation state in β-Na0.7[Mn1-xLix]O2+y is carefully controlled without the inclusion of impurities. Through various in situ and ex situ analyses including X-ray diffraction, X-ray absorption near-edge structure spectroscopy, and inductively coupled plasma mass spectrometry, we clarify the dependence of (i) reaction mechanisms on disordered Li distribution in the Mn layer, (ii) reversible capacities on the initial Mn oxidation state, (iii) redox potentials on the Jahn-Teller distortion, (iv) capacity fading on phase transitions during charging and discharging, and (v) electrochemical performance on Li dopant vs Mn vacancy. Finally, we demonstrate that the optimized β-Na0.7[Mn1-xLix]O2+y (x = 0.07) exhibits excellent electrochemical performance including a high reversible capacity of ∼183 mA h g-1 and stable cycle performance over 120 cycles.

Modifying exchange bias effects of Mn/NiFe bilayers by in-situ Ar+ bombardment

In this work, we present a procedure to modify the exchange bias (EB) properties of antiferromagnetic Mn/ferromagnetic NiFe bilayers by in-situ low energy Ar+ bombardment of the Mn layer during sample deposition. We present structural and magnetic results for unassisted and Ar+ assisted Mn/NiFe bilayers. X-ray diffraction, transmission electron microscopy and electron diffraction results establish different preferred Mn orientation directions between the two samples as a result of the Ar+ bombardment process. Hysteresis loops taken over several temperatures reveal that samples assisted with Ar+ ions during the Mn layer deposition had suppressed EB properties at low temperature as compared to samples grown without Ar+ assistance.

Characterization and differentiation of rock varnish types from different environments by microanalytical techniques

We investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques. These techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer- to nanometer-sized structures in these geological materials. Femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS), scanning transmission X-ray microscopy-near edge X-ray adsorption fine structure spectroscopy (STXM-NEXAFS) in combination with scanning electron microscopy (SEM) of focused ion beam (FIB) ultra-thin (100–200nm) sections, conventional and polarization microscopy, as well as electron paramagnetic resonance (EPR) measurements were used to obtain information about these rock varnishes.Rock varnishes from different environments, which cannot readily be distinguished based on their macroscopic appearance, differ significantly in their constituent elemental mass fractions, e.g., of Mn, Fe, Ni, Co, Ba, and Pb, and their rare earth element (REE) patterns. Structural characteristics such as the particle sizes of embedded dust grains, internal structures such as layers of Mn-, Fe-, and Ca -rich material, and structures such as cavities varied between varnishes from different environments and regions in the world. The EPR spectra were consistent with aged biogenic Mn oxides in all samples, but showed subtle differences between samples of different origin.Our observations allow us to separate rock varnishes into different types, with differences that might be indicators of distinct geneses. Five different types of rock varnish could be distinguished, Type I–V, of which only Type I might be used as potential paleoclimate archive. Each varnish type has specific characteristics in terms of their elemental composition, element distribution, and structures. The combination of element ratios (Mn/Ba, Al/Ni, Mn/REY, Mn/Ce, Mn/Pb, LaN/YbN, and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other.

Magneto-optical Kerr spectroscopy of (Ga,Mn)(As,P) ferromagnetic layers: Experiments and k.p theory

We present a theoretical and experimental study of the magneto-optical properties of thin (Ga,Mn)(As,P) layers on GaAs substrates with varying phosphorus fractions. Using a 40-band k.p model as well as an antiferromagnetic (s, p)-d exchange interaction, we calculate the dielectric tensor, the Kerr rotation angle, and the ellipticity in the interband transition region. Our calculations are validated through a set of accurate comparisons with experimental results. The Kerr ellipticity peak is found to be 2 to 3 times larger than the Kerr rotation angle both experimentally and theoretically. This work will enable to optimize the magneto-optical effects in these layers for maximum sensitivity in ultra-fast magnetization dynamics and domain microscopy experiments.

Magnetic properties and structure of low temperature phase MnBi with island structure

The magnetic properties of the low temperature phase (LTP) MnBi thin films of islands structure are discussed. The LTP MnBi islands are formed onto silica substrates after the multilayers Bi(3.2nm)/Mn(2nm)x N are deposited and then annealed at 450C for 0.5hr, where N is the number of the repetition of a pair of Mn and Bi layer. Those islands are found to be of the LTP MnBi, with the c-axis orientation along the normal to the sample plane for N=10 ∼ 40. Their size vary from place to place, but are averagely of about a few hundred nm in height and a few μm in width for N from 10 to 40. For N=200, the elongated islands are formed densely, with the length of about a few tens of μm. The coverage of those islands increases with N. The temperature dependence of saturation magnetization Ms is qualitatively similar to that for bulk, though the absolute values for Ms are smaller by 20%. The magnetic anisotropy constants of Ku1 and Ku2 are evaluated for the samples with N=10 ∼ 40, where Ku1 and Ku2 are the magnetic anisotropy constants corresponding to the second and fourth power term in the uniaxial magnetic anisotropy energy expression. It is found that the Ku1 increases with T monotonously, reaching to about 1x107 erg/cc at 400K. On the other hand, the Ku2 remains nearly zero for temperatures below 300K, and then becomes negative, reaching to about 7 x 106 erg/cc at 400K. This is the first to report of the temperature dependence of Ku1 and Ku2 in the LTP MnBi of an island structure. It is also noted that the decrease of Ku for a temperature range beyond around 450 K is possibly due to the decrease of the Ku2 component, as demonstrated in the present study.

Initial Oxidation Behavior of Ferritic Stainless Steel with Sputtered Mn–Cu Coating

Initial oxidation behavior of SUS 430 steel with a sputtered Mn–Cu coating was investigated in air at 800 °C. It was found that Mn was preferrentially oxidized upon thermal exposure from 2 to 10 min. The surface scale mainly consisted of MnO inner layer and Mn3O4 outer layer, although a small amount of Fe was observable in the scale. In addition, CuO developed on the outer surface of the scale after 10 min of oxidation. However, the scale formed on the coated steel upon oxidation for 20–300 min was obviously different from that upon oxidation for 2–10 min. It was composed of a tri-layer containing a top layer of CuO, a middle layer of (Mn,Cu)3O4 with some Fe, and an inner layer of Cr-rich oxide from the outer surface to the interface between scale and steel. With increasing oxidation time, furthermore, the top layer of CuO thickened first and then became thin. The oxidation mechanism was discussed.

Magnetic studies of spin wave excitations in Fe/Mn multilayers

The structural and magnetic properties of Fe/Mn multilayers grown by thermal evaporation technique were investigated by transmission electron microscopy, vibrating sample magnetometer and spin wave theory. Transmission electron microscopy shows that the Fe and Mn layers are continuous with a significant interfacial roughness. The magnetic properties of Fe/Mn multilayers were studied for various Fe thicknesses (tFe). The change of magnetization as a function of temperature is well depicted by a T3/2 law. The Fe spin-wave constant was extracted and found to be larger than that reported for bulk Fe, which we attribute to the fluctuation of magnetic moments at the interface, due to the interfacial roughness. The experimental M (T) data were satisfactory fitted for multilayers with different Fe thicknesses; and several exchange interactions were extracted.

Solid state synthesis of Mn5Ge3 in Ge/Ag/Mn trilayers: Structural and magnetic studies

The thin-film solid-state reaction between elemental Ge and Mn across chemically inert Ag layers with thicknesses of (0, 0.3, 1 and 2.2µm) in Ge/Ag/Mn trilayers was studied for the first time. The initial samples were annealed at temperatures between 50 and 500°C at 50°C intervals for 1h. The initiation temperature of the reaction for Ge/Mn (without a Ag barrier layer) was ~ 120°C and increased slightly up to ~ 250°C when the Ag barrier layer thickness increased up to 2.2µm. In spite of the Ag layer, only the ferromagnetic Mn5Ge3 compound and the Nowotny phase were observed in the initial stage of the reaction after annealing at 500°C. The cross-sectional studies show that during Mn5Ge3 formation the Ge is the sole diffusing species. The magnetic and cross-sectional transmission electron microscopy (TEM) studies show an almost complete transfer of Ge atoms from the Ge film, via a 2.2µm Ag barrier layer, into the Mn layer. We attribute the driving force of the long-range transfer to the long-range chemical interactions between reacting Mn and Ge atoms.

First principles study of c-axis strain effect on the magnetic structure and ferroelectricity in double perovskite Y2MnCrO6

We carry out a first-principles investigation of the c-axis strain effect on the structure and multiferroicity of double perovskite Y2MnCrO6, in which the b-axis is fixed to the bulk value. The results show that the ferrimagnetic-paraelectric ground state in strain-free bulk sample is driven to a multiferroic E-type antiferromagnetic-ferroelectric state under the c-axis compressive strains above −0.3%. We also find a ferrimagnetic-to-ferromagnetic phase transition at the c-axis tensile strain of 2.2%, due to remarkably reduced octahedral distortion. Heisenberg model analysis reveals that the two phase transitions are predominantly governed by the nearest-neighboring exchange interaction in Mn layer and that along the c-axis. Moreover, the former magnetic transition under compressive strain gives rise to a finite ferroelectric polarization mainly due to the electronic contribution. The predicted polarization in the multiferroic state is significantly enhanced as compared to that of undoped orthorhombic YMnO3 and decreases monotonously with the c-axis compressive strain.