Mn Layers Research Articles

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.

Structural and transport properties ofGaAs/δ-Mn/GaAs/InxGa1−xAs/GaAs quantum wells

We report results of investigations of the structural and transport properties ofGaAs/Ga1−xInxAs/GaAs quantum wells (QWs) having a 0.5–1.8 monolayer (ML) thick Mn layer, separatedfrom the QW by a 3 nm thick spacer. The structure has hole mobility of about2000 cm2 (V s)−1, being by several orders of magnitude higher than in known ferromagnetic two-dimensional(2D) structures. The analysis of the electro-physical properties of these systems is based ondetailed study of their structure by means of high-resolution x-ray diffractometry andglancing-incidence reflection, which allow us to restore the depth profiles of the structuralcharacteristics of the QWs and thin Mn-containing layers. These investigations showthe absence of Mn atoms inside the QW. The quality of the structures was alsocharacterized by photoluminescence spectra from the QWs. The transport propertiesreveal features inherent to ferromagnetic systems: a specific maximum in thetemperature dependence of the resistance and the anomalous Hall effect (AHE)observed in samples with both ‘metallic’ and activated types of conductivity up to∼100 K. AHE is most pronounced in the temperature range where the resistance maximum isobserved. The results are discussed in terms of the interaction of 2D-holes and magneticMn ions in the presence of large-scale potential fluctuations related to the randomdistribution of Mn atoms. The AHE values are compared with calculations taking intoaccount the ‘intrinsic’ mechanism in ferromagnetic systems.

Formation of Zn–Ca phyllomanganate nanoparticles in grass roots

It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33Å in the ab plane and contain only 1.2 layers (∼8.6Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn–Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere.

Exchange bias and spin valve systems with Fe–Mn antiferromagnetic pinning layers, obtained by the thermo-ionic vacuum arc method

Exchange bias and spin valve systems with Fe–Mn antiferromagnetic layers of different Fe concentrations were obtained by the thermo-ionic vacuum arc method. The adherence of the multilayer system to the Si substrate depends on the Fe–Mn composition. The overall roughness depends on the growing order of the antiferromagnetic/ferromagnetic layers. Very low blocking temperatures for exchange bias were observed for the considered compositions of the Fe–Mn layer. The coercive forces of both the pinned and the free layers of spin valve structures can be considerably modified along a large set of samples simultaneously prepared.

Ichnological record of deep-sea palaeoenvironmental changes around the Oceanic Anoxic Event 2 (Cenomanian–Turonian boundary): An example from the Barnasiówka section, Polish Outer Carpathians

Trace fossil assemblages including Planolites, Thalassinoides, Palaeophycus, Taenidium, Chondrites and Trichichnus have been determined in the Upper Cenomanian turbiditic deep-water succession, corresponding to the pre-OAE-2 interval in the Barnasiówka–Ostra Góra section, the Skole Nappe, Polish Outer Carpathians. These assemblages indicate that oxygenation within sediment fluctuated from oxic to dysoxic zone. The overlying uppermost Cenomanian organic-rich facies (Bonarelli-equivalent horizon), corresponding to the main interval of the OAE-2 contains black shale layers, devoid of trace fossils representing anoxic (euxinic) events, and green shales that include Chondrites, Planolites and Thalassinoides, recording dysoxic intervals. Three subintervals (phases) within the OAE-2 sediments have been distinguished in the Barnasiówka section, based on trace fossil diversity, ichnofabrics and chemical redox indices. These phases correspond to intervals with various intensity of sea floor oxygenation. Ichnofabrics within the OAE-2 succession was also controlled by consistency of sediment. Post-OAE-2 interval recorded by the earliest Turonian red and green siliceous–manganiferous shales and two Fe–Mn layers represent sediments deposited in well oxygenated conditions under extremely low sedimentation rate. Most of the shales are parallel-laminated, and they do not include any benthic microfossils and trace fossils, however some of the red and green layers display cryptic bioturbation. These features are related to food scarcity, cessation of gravity flows, unfavorable characteristics of bottom water, and a low consistency of substrate.

Carrier-mediated ferromagnetism in p-Si(100) by sequential ion-implantation of B andMn

Ferromagnetic Si1−xMnx wasprepared by implanting B+ and Mn+ ions in sequence into p-type Si(100) at room temperature and post-annealing at700–900 °C. Superparamagnetic nano-sized silicide precipitates, 10–27 at.% Mn, were found near the surface of allSi1−xMnx samples.Annealing at 800 °C or below leads to the formation of a thin Si(Mn) layer, with 1.1 at.% Mn,∼180 nm beneath the surface, giving rise to ferromagnetism with a Curie temperatureabove 250 K. The high-temperature ferromagnetism is attributed to the indirectexchange mediated by localized carriers in the impurity states. The Mn content of1–1.5 at.%, having been separately reported to show room-temperature ferromagnetismseveral times by different groups, seems meaningful for Si-based diluted magneticsemiconductors (DMS). Possible extensions of our work presented here are elucidated.

Synthesis and electrochemical properties of Co,Mn-coated LiNiO 2 lithium-ion battery cathode materials

Effect of a Co,Mn coating on the structure and electrochemical properties of the LiNiO 2 cathode material was investigated using XRD, TEM, XPS, cyclic voltammetry and EIS. Co,Mn coating formed not only a thin layer but a solid solution by interacting with core material on the surface LiNiO 2 cathode particles. Co,Mn-coated LiNiO 2 behaved much better, losing about 8.9% of its initial capacity (181.3 mAh g −1) after 50 cycles at 150 mAg −1. While the uncoated LiNiO 2 lost about 26.9% of its initial capacity (183.3 mAh g −1). Based on these results from composition analysis and electrochemical tests, it was found that the coating layer consisted of Co,Mn particles attached to the particle surface and the Co,Mn layer significantly improved the electrochemical properties of the cathode by not only suppressing the phase transition but also decreasing the impedance growth at the interface between the electrodes and the electrolyte during charge–discharge cycling.

Mn local order in room temperature ferromagnetic Mn/ZnO multilayers

The local environment of Mn atoms in(ZnO30 Å/Mnt)n multilayers (ML) has been studied by means of x-ray absorption spectroscopyat the Mn K edge. A series of ML has been prepared by sputtering withapproximately constant total amount of Mn (300 Å) while the Mn layer thickness(t) has been varied from 60 to 1 Å (modifying consequently the number of Mn–ZnOinterfaces) in order to study the Mn–Zn–O system. Variation of the Mn layer thickness(t) has been directly associated with changes in the Mn oxidation stateswithin the sample series. Absorption spectroscopy results for films witht≤15 Å indicatemostly MnO2 formation and no signal of Mn in the ZnO lattice is found. Conversely, films witht≥30 Å present two different Mn environments, that have been relatedto the coexistence of rocksalt and wurtzite phases, formed byZn1−xMnxO mixed solid solutions. The magnetic behaviour of samples is correlated with structuralproperties. That correlation strongly points towards substitutional Mn in the wurtzitephase as the origin of the observed ferromagnetism above room temperature.

Magnetic properties of the mixed-valence manganese oxidePb3Mn7O15

A Pb3Mn7O15 single crystal has been grown by the flux method and studied using x-raydiffraction and magnetization measurements. The crystal is hexagonal(P63/mcm spacegroup, Z = 4) and exhibits a pronounced layered nature. Along the [001] direction(c axis), the structure consists of layers of edge-sharingMnO6 octahedra. Pairs of Mn atoms occupy the octahedral sites located between layers forming ‘bridges’ alongthe c axis, which link neighboring Mn layers. The magnetic properties of the crystal have beeninvestigated using ac and dc magnetization measurements in the temperature range 2–900 K atmagnetic fields up to 90 kOe. The experimental data obtained suggest that in the temperatureregion under study several different magnetic phases can be distinguished. Down to∼250 K, the crystal is in the paramagnetic state. Below this temperature, short-rangeantiferromagnetic ordering apparently starts forming within Mn layers, although atransition to long-range magnetic order occurs at 70 K. The magnetization data obtainedleads us to conclude that this state is canted antiferromagnetic with moments lying in thebasal plane of the crystal. In addition, below 20 K the crystal undergoes one more magnetictransition that corresponds to spin reorientation.

Novel strategies for rapid trace element analysis of polyamide by graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. Dissolution in an organic solvent versus direct solid sampling approaches.

Titanium dioxide is added to polyamide since it efficiently scatters visible light and imparts whiteness, brightness and high opacity. TiO2, however, can degrade easily and to counteract this, it is coated with a layer of inorganic material, containing Al, Mn and Si. For quality control, it is important to develop fast and reliable methods for the determination of these elements. Due to the fact that acid digestion techniques are labor-intensive, time-consuming and bring about the risk of contamination, an alternative dissolution procedure has been developed using formic acid to dissolve polyamide. The solutions thus obtained were measured by means of graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma mass spectrometry (ICPMS). For the latter technique, sample introduction was performed using a pneumatic nebulization system, containing a membrane desolvating unit to remove the organic solvent. This approach provided satisfactory results in terms of precision (6–10% RSD) and limits of detection (0.1–0.6 μg g−1, except for Si when using ICPMS). Addition of formic acid to the calibration standards was demonstrated to be required. To enhance the sensitivity, increase the sample throughput and reduce the risk of contamination and/or analyte losses, the direct solid sampling methods solid sampling GFAAS and electrothermal vaporization (ETV)-ICPMS were also evaluated. Both techniques provided accurate results using calibration versus aqueous standards, with RSD values of ∼10%. Limits of detection were improved considerably compared to those attainable after dissolution. In contrast to GFAAS, ETV-ICPMS allows the simultaneous determination of all of the analytes.

Formation of Mn Oxide with Thermal CVD and its Diffusion Barrier Property Between Cu and SiO2

ABSTRACTA manganese oxide layer was formed by thermal chemical vapor deposition(CVD) on a tetraethylorthosilicate (TEOS) oxide substrate. The thickness of the Mn oxide layer could be varied 2.6 to 10 nm depending on deposition temperature. Heat-treated samples of PVD Cu / CVD Mn oxide /SiO2 indicated no interdiffusion. The CVD Mn oxide was found to be a good diffusion barrier layer.

Enhancement of exchange bias by ultra‐thin Mn layer insertion at the interface of Mn‐Ir/Co‐Fe bilayers

AbstractEffects of ultra‐thin Mn, Ru, Pd, Ta, Gd, and Tb layer insertion at the interface on the exchange bias of Mn75Ir25/Co70Fe30 bilayers were investigated. Unidirectional anisotropy constant, JK, of the bilayer was significantly enhanced from 0.46 erg/cm2 to 0.84 erg/cm2 with the insertion of 0.5‐nm‐thick Mn layer, while it was reduced with increasing the inserted layer thickness for the other materials. The value of 0.84 erg/cm2 was not obtained in the variation of JK with respect to the chemical composition of Mn‐Ir layer in a range of Ir content of 0 ∼ 40 at.%. The cause of the enhancement of JK with ultra‐thin Mn insertion might be due to the modification of antiferromagnetic spin structure at the interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

P.1.e.026 A functional MRI study of the brain and interpersonal behaviour in schizophrenia. A preliminary study

Todorokite is considered to form from vernadite in nature and commonly concentrates nickel. However, this mineralogical transformation has never been imaged nor explained mechanistically, and its effect on the uptake of nickel has never been quantified at the molecular-level. We have characterized these reactions at the macroscopic, microscopic, nanoscopic and atomic scales in a marine manganese concretion by combining transmission electron microscopy, electron and X-ray microprobe analysis, powder and micro X-ray diffraction, and Mn and Ni K-edge EXAFS spectroscopy. The concretion was collected during the Ticoflux II expedition near the Nicoya Peninsula, Costa Rica, and is representative of Mn deposits in hemipelagic sediments. It consists of 5 to 25 μm aggregates, shaped like sea-urchins, with a core of 7Å-vernadite (1.0 wt% Ni), a rim of 10Å-vernadite (3.8 wt% Ni), and an outermost region of todorokite fibers (1.9 wt% Ni) that extend outwards. The crystallites of 7Å-vernadite are single- to bi-layered, with hexagonal layer symmetry (a = b = 2.83 Å), and an average structural formula of Mg0.1612+Ca0.0102+K0.016+[Mn0.9024+Vac0.083Ni0.0152+]O2·nH2O. The crystallites of 10Å-vernadite contain 10 to 20 layers semi-coherently stacked in the ab plane and uniformly separated in the [0 0 1] direction by ∼9 Å due to the intercalation of hydrated Mg2+ cations. The average structural formula of 10Å-vernadite is Mg0.1872+Ca0.0162+K0.013+[Mn0.8644+Vac0.074Ni0.0622+]O2·nH2O if the layers contain vacancy sites, or alternately Mg0.2022+Ca0.0182+K0.014+[Mn0.6134+Mn0.3203+Ni0.0672+]O2·nH2O, if they contain Mn3+. The average formula of todorokite is Mg0.1782+Ca0.0132+K0.019+[Mn0.6124+Mn0.3563+Ni0.0322+]O2·nH2O.A genetic model is proposed based on combining these new data with previously published results. The thermodynamically unstable 7Å-vernadite transforms via dissolution-recrystallization to semi-ordered Mg-rich 10Å-vernadite. Nickel is released from dissolved biogenic silica or reduced organic matter, and taken up mainly in the Mn layer of 10Å-vernadite. Interlayer magnesium serves as a template to the further topotactic transformation of 10Å-vernadite to todorokite. The dimension of the todorokite tunnels in the [0 0 1] direction is uniform and determined by the size of the hydrated Mg2+ ion (8.6 Å). The tunnel dimension in the [1 0 0] direction depends on the density of Mg2+ in the interlayer and the superstructure of the phyllomanganate layer. If the parent phyllomanganate contains high amounts of Mg2+ (i.e., high layer charge), or Mn3+ and Mn4+ cations ordered following the Mn3+–Mn4+–Mn4+ sequence as in synthetic triclinic birnessite, then the tunnel dimension is ideally 3 × 3 octahedral chain widths in both crystallographic directions. Otherwise, the tunnel dimension is incoherent in the [1 0 0] direction (i.e., T(3,n) tunnel structure), as has been observed in all natural todorokites. Natural todorokite is defective because the precursor natural phyllomanganates either have a layer charge deficit below 0.33e per octahedral site, or rarely are triclinic birnessite. The abundance of Mg in seawater and its key role in converting phyllomanganate to tectomanganate with T(3,n) tunnel structure explain why todorokite is common in marine ferromanganese oxides, and seldom present in terrestrial environments. The topotactic phase transformation described here is the only known route to todorokite crystallization. This implies that all natural todorokites may be authigenic because they are formed in situ from a phyllomanganate precursor.

P.1.e.025 Altered white matter tracts in subjects at high genetic risk of schizophrenia by diffusion tensor tractography

Todorokite is considered to form from vernadite in nature and commonly concentrates nickel. However, this mineralogical transformation has never been imaged nor explained mechanistically, and its effect on the uptake of nickel has never been quantified at the molecular-level. We have characterized these reactions at the macroscopic, microscopic, nanoscopic and atomic scales in a marine manganese concretion by combining transmission electron microscopy, electron and X-ray microprobe analysis, powder and micro X-ray diffraction, and Mn and Ni K-edge EXAFS spectroscopy. The concretion was collected during the Ticoflux II expedition near the Nicoya Peninsula, Costa Rica, and is representative of Mn deposits in hemipelagic sediments. It consists of 5 to 25 μm aggregates, shaped like sea-urchins, with a core of 7Å-vernadite (1.0 wt% Ni), a rim of 10Å-vernadite (3.8 wt% Ni), and an outermost region of todorokite fibers (1.9 wt% Ni) that extend outwards. The crystallites of 7Å-vernadite are single- to bi-layered, with hexagonal layer symmetry (a = b = 2.83 Å), and an average structural formula of Mg0.1612+Ca0.0102+K0.016+[Mn0.9024+Vac0.083Ni0.0152+]O2·nH2O. The crystallites of 10Å-vernadite contain 10 to 20 layers semi-coherently stacked in the ab plane and uniformly separated in the [0 0 1] direction by ∼9 Å due to the intercalation of hydrated Mg2+ cations. The average structural formula of 10Å-vernadite is Mg0.1872+Ca0.0162+K0.013+[Mn0.8644+Vac0.074Ni0.0622+]O2·nH2O if the layers contain vacancy sites, or alternately Mg0.2022+Ca0.0182+K0.014+[Mn0.6134+Mn0.3203+Ni0.0672+]O2·nH2O, if they contain Mn3+. The average formula of todorokite is Mg0.1782+Ca0.0132+K0.019+[Mn0.6124+Mn0.3563+Ni0.0322+]O2·nH2O.A genetic model is proposed based on combining these new data with previously published results. The thermodynamically unstable 7Å-vernadite transforms via dissolution-recrystallization to semi-ordered Mg-rich 10Å-vernadite. Nickel is released from dissolved biogenic silica or reduced organic matter, and taken up mainly in the Mn layer of 10Å-vernadite. Interlayer magnesium serves as a template to the further topotactic transformation of 10Å-vernadite to todorokite. The dimension of the todorokite tunnels in the [0 0 1] direction is uniform and determined by the size of the hydrated Mg2+ ion (8.6 Å). The tunnel dimension in the [1 0 0] direction depends on the density of Mg2+ in the interlayer and the superstructure of the phyllomanganate layer. If the parent phyllomanganate contains high amounts of Mg2+ (i.e., high layer charge), or Mn3+ and Mn4+ cations ordered following the Mn3+–Mn4+–Mn4+ sequence as in synthetic triclinic birnessite, then the tunnel dimension is ideally 3 × 3 octahedral chain widths in both crystallographic directions. Otherwise, the tunnel dimension is incoherent in the [1 0 0] direction (i.e., T(3,n) tunnel structure), as has been observed in all natural todorokites. Natural todorokite is defective because the precursor natural phyllomanganates either have a layer charge deficit below 0.33e per octahedral site, or rarely are triclinic birnessite. The abundance of Mg in seawater and its key role in converting phyllomanganate to tectomanganate with T(3,n) tunnel structure explain why todorokite is common in marine ferromanganese oxides, and seldom present in terrestrial environments. The topotactic phase transformation described here is the only known route to todorokite crystallization. This implies that all natural todorokites may be authigenic because they are formed in situ from a phyllomanganate precursor.

Formation of todorokite from vernadite in Ni-rich hemipelagic sediments

Todorokite is considered to form from vernadite in nature and commonly concentrates nickel. However, this mineralogical transformation has never been imaged nor explained mechanistically, and its effect on the uptake of nickel has never been quantified at the molecular-level. We have characterized these reactions at the macroscopic, microscopic, nanoscopic and atomic scales in a marine manganese concretion by combining transmission electron microscopy, electron and X-ray microprobe analysis, powder and micro X-ray diffraction, and Mn and Ni K-edge EXAFS spectroscopy. The concretion was collected during the Ticoflux II expedition near the Nicoya Peninsula, Costa Rica, and is representative of Mn deposits in hemipelagic sediments. It consists of 5 to 25 μm aggregates, shaped like sea-urchins, with a core of 7Å-vernadite (1.0 wt% Ni), a rim of 10Å-vernadite (3.8 wt% Ni), and an outermost region of todorokite fibers (1.9 wt% Ni) that extend outwards. The crystallites of 7Å-vernadite are single- to bi-layered, with hexagonal layer symmetry ( a = b = 2.83 Å), and an average structural formula of Mg 0.161 2 + Ca 0.010 2 + K 0.016 + [ Mn 0.902 4 + Vac 0.083 Ni 0.015 2 + ] O 2 · n H 2 O . The crystallites of 10Å-vernadite contain 10 to 20 layers semi-coherently stacked in the ab plane and uniformly separated in the [0 0 1] direction by ∼9 Å due to the intercalation of hydrated Mg 2+ cations. The average structural formula of 10Å-vernadite is Mg 0.187 2 + Ca 0.016 2 + K 0.013 + [ Mn 0.864 4 + Vac 0.074 Ni 0.062 2 + ] O 2 · n H 2 O if the layers contain vacancy sites, or alternately Mg 0.202 2 + Ca 0.018 2 + K 0.014 + [ Mn 0.613 4 + Mn 0.320 3 + Ni 0.067 2 + ] O 2 · n H 2 O , if they contain Mn 3+. The average formula of todorokite is Mg 0.178 2 + Ca 0.013 2 + K 0.019 + [ Mn 0.612 4 + Mn 0.356 3 + Ni 0.032 2 + ] O 2 · n H 2 O . A genetic model is proposed based on combining these new data with previously published results. The thermodynamically unstable 7Å-vernadite transforms via dissolution-recrystallization to semi-ordered Mg-rich 10Å-vernadite. Nickel is released from dissolved biogenic silica or reduced organic matter, and taken up mainly in the Mn layer of 10Å-vernadite. Interlayer magnesium serves as a template to the further topotactic transformation of 10Å-vernadite to todorokite. The dimension of the todorokite tunnels in the [0 0 1] direction is uniform and determined by the size of the hydrated Mg 2+ ion (8.6 Å). The tunnel dimension in the [1 0 0] direction depends on the density of Mg 2+ in the interlayer and the superstructure of the phyllomanganate layer. If the parent phyllomanganate contains high amounts of Mg 2+ (i.e., high layer charge), or Mn 3+ and Mn 4+ cations ordered following the Mn 3+–Mn 4+–Mn 4+ sequence as in synthetic triclinic birnessite, then the tunnel dimension is ideally 3 × 3 octahedral chain widths in both crystallographic directions. Otherwise, the tunnel dimension is incoherent in the [1 0 0] direction (i.e., T(3, n) tunnel structure), as has been observed in all natural todorokites. Natural todorokite is defective because the precursor natural phyllomanganates either have a layer charge deficit below 0.33e per octahedral site, or rarely are triclinic birnessite. The abundance of Mg in seawater and its key role in converting phyllomanganate to tectomanganate with T(3, n) tunnel structure explain why todorokite is common in marine ferromanganese oxides, and seldom present in terrestrial environments. The topotactic phase transformation described here is the only known route to todorokite crystallization. This implies that all natural todorokites may be authigenic because they are formed in situ from a phyllomanganate precursor.

Ferromagnetic Resonance and Hall Effect Characterization of GaMnSb Layers

The electrical and magnetic properties of GaSb:Mn layers deposited on (100)GaAs substrates from a laser plasma in vacuum have been studied. It is shown that the films deposited at 200–440 °C are mosaic single crystalline and epitaxial to the substrate, with p-type conduction. Manganese-doped layers had a hole concentration higher than 1×1019 cm−3 and fairly high values of mobility (up to 40 cm2/V s at 300 K). The layers grown at 200 °C exhibited an anomalous Hall effect up to approximately room temperature. On the contrary, a normal Hall effect was observed in the layers grown at 440 °C. Ferromagnetic resonance measurements have revealed the existence of ferromagnetism in the sample grown at 200 °C. The transition temperature is close to room temperature, in full agreement with the Hall data. In the sample grown at 440 °C, the formation of ferromagnetic clusters has tentatively been concluded.

Correlation between Mn oxidation state and magnetic behavior in Mn/ZnO multilayers prepared by sputtering

Compositional, microstructural, and magnetic characterization of [ZnO(30 Å)/Mn(x)]n multilayers prepared by sputtering is presented to study the observed ferromagnetism in the Mn-ZnO system. The nominal Mn layer thickness, x, is varied from 3 to 60 Å, while the number of bilayers, n, is increased to maintain the total amount of Mn constant. Microstructure information was deduced from x-ray reflectivity, Mn oxidation state was determined by x-ray absorption spectroscopy, and magnetic properties were measured over a temperature range of 5–400 K. Magnetic behavior of these samples is found to be related to the Mn layer thickness (x). Multilayers with x≥30 Å exhibit ferromagnetism with a Curie temperature above 400 K, while mostly paramagnetic behavior is obtained for x<15 Å. Magnetic behavior is discussed in terms of electronic and structural parameters of samples. Mn-ZnO interface effect is related to the ferromagnetic order of the samples, but it is not a sufficient condition. The essential role of the Mn oxidation state in the magnetic behavior of this system is pointed out. It is shown a correlation between the obtained ferromagnetism and a Mn oxidation state close to 2+.

Perpendicular Antiferromagnetic Ordering of Mn and Exchange Anisotropy inFe/MnMultilayers

Fe/Mn is a model system in which to study exchange bias, since the antiferromagnetic (AF) Mn layers are believed to have uncompensated moments with all spins aligned in the plane and parallel to those of the Fe. We have determined the microscopic AF ordering at the interfaces using single-crystal neutron diffraction. An unexpected magnetic structure is obtained, with out-of-plane Mn moments perpendicular to those of Fe. This explains the low bias field and shows that the simple AF ordering assumed in a variety of exchange-biased systems may well have to be revised.

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured thin-film EL device

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured (NS) thin-film electroluminescent (TFEL) device of which emission layer is a multilayer composed with ZnS:Mn layers and 0.7-nm-thick AlN interlayers were studied. The bandgap widening and the increased PL efficiency of Mn 2+ 3d–3d transitions with a decrease in the ZnS:Mn single-layer thickness down to 5 nm were observed, which is ascribed to quantum confinement effects. Meanwhile, the multilayer with 2-nm-thick ZnS:Mn single-layers shows a drop of PL efficiency, indicating the presence of defective region just on AlN. The tendency of the luminous efficiency of the NS-TFEL device against the ZnS:Mn single-layer thickness is similar to the tendency found in the PL efficiency, indicating the importance of the ZnS:Mn/AlN interface for the device performance.

Low-temperature transport and ferromagnetism in GaAs-based structures with Mn

GaAs structures with implanted Mn and, additionally, with Mg for increasing the hole concentration in the implanted Mn layer are synthesized and investigated. SQUID magnetometer measurements revealed the existence of ferromagnetism in the temperature range 4.2 K ≤ T < 400 K, which is associated with the formation of the Ga1−xMnxAs solid solution and MnAs and Ga1−yMny clusters in the sample as a result of rapid high-temperature annealing. At temperatures from 4.2 to approximately 200 K, the anomalous Hall effect associated with additional magnetization of the sample is observed. As the temperature increases from 4.2 K, the colossal negative magnetoresistance is transformed into a positive magnetoresistance at T ≈ 35 K.