Mn Layer Thickness Research Articles

Highly Luminescent Manganese‐Doped 2D Hybrid Perovskite Nanoplatelets with Dual Emissions Controlled Through Layer Thickness Modulation

AbstractDoping semiconductor nanomaterials with manganese ion (Mn2+) introduce a well‐defined photoactive d‐d level within the band structure, paving the way for diverse applications. Although Mn doping in single‐layer 2D hybrid perovskites (n = 1) has been extensively studied, limited research has been conducted on doping with modulation of the layer thickness. Herein, Mn2+ doping in hybrid 2D perovskite nanoplatelets (NPLs), L2An‐1[Pb1‐xMnx]nBr3n+1 (where L = butylammonium, A = methylammonium), with variations in Mn concentration (x = 0–0.60) and layer thickness (n = 1–3) is reported. Substitutional doping of Mn significantly increases the photoluminescence quantum yield as well as the rate of energy transfer efficiency, which strongly depends on the layer thickness of NPLs. The Mn concentration in 2D NPLs determines the rate of forward and backward energy transfer. Low‐temperature emission spectra allow to determine thickness‐dependent exciton binding energy for Mn‐doped 2D NPLs (x = 0.5) with values of 410 ± 11 meV (n = 1), 188 ± 9 meV (n = 2), and 151 ± 17 meV (n = 3). The faster dissociation of band‐edge excitons into free carriers at Mn2+ sites results in high brightness with an excellent CRI of 89.2 for the white light‐emitting diode.

Structural and magnetic properties of Pt/Co/Mn-based multilayers

Magnetic multilayers are a rich class of material systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here, we present a comprehensive experimental study of the system Pt/Co/Mn, which extends the group of $\mathrm{Pt}/\mathrm{Co}/X$ ($X=$ metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out of plane to in plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubblelike domains---potentially even magnetic skyrmions---in the case of sufficiently thick Mn layers, which are expected to contribute to a sizable Dzyaloshinskii-Moriya interaction in the multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications.

Influence of fabrication parameters on the magnetic and structural properties of Mn5Ge3

Mn5Ge3 is a ferromagnetic material with the high potential for spintronic applications. Usually, it is grown by conventional solid state reaction of manganese with germanium using molecular beam epitaxy. Here, we report the structural and magnetic properties of Mn5Ge3 layers grown on Ge substrates using ultrafast-solid phase epitaxy (SPE) method. We investigate the influence of the substrate orientation, Mn layer thickness and annealing parameters on the crystallographic orientation and magnetization of Mn5Ge3. It is shown that after millisecond range SPE, Mn5Ge3 films always have a preferred (100) orientation whether grown on Ge (001) or (111) substrates, which determines the orientation of the magnetization easy axis lying in the film plane along c axis independent of the layer thickness. The Curie temperature of Mn5Ge3 weakly depends on fabrication parameters.

The magnetic properties of Mn5Ge3 thin films grown on PMN-PT

The authors report the thickness dependent structural and magnetic properties of Mn5Ge3 thin films with different Mn layer thicknesses in the range from 5 nm to 30 nm deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) substrates using solid phase epitaxy. Gradual decrease of the surface roughness due to the formation of larger grains, as well as the decrease of the coercivity and squareness ratio on increasing of Mn layer thickness has been observed. It has been revealed that the slightly greater value of the saturation magnetization than the corresponding one observed early for thin films and bulk samples isassociated withthe presence ofstructural defects. The ferromagnetic resonance (FMR) spectra have been obtained to be isotropic for the films with 5 nm thickness, whereas those registered from the films with the thicknesses of 10 nm and above demonstrated in-plane magnetic anisotropy, which have been interpreted as to be resulted from magnetocrystalline anisotropy as well as the stress-induced magnetic anisotropy. These results are suggested to create a major interest in the development of magnetoelectric heterostructured devices based on strain coupling that are compatible with CMOS technology.

Perpendicular magnetic tunnel junctions with Mn-modified ultrathin MnGa layer

Perpendicular magnetic tunnel junctions (p-MTJs) with a MgO barrier and a 1-nm-thick MnGa electrode were investigated by inserting several monolayers (MLs) of Mn. The tunnel magnetoresistance (TMR) ratio systematically increased when increasing the Mn layer thickness with a maximum of 18 (38.4)% at 300 (5) K for a Mn layer thickness of 0.6–0.8 nm. This ratio is five times higher compared to that without the Mn layer. The perpendicular magnetic anisotropy (PMA) field and the PMA constant of the ultrathin MnGa layer also increased up to 62–90 kOe and 6.2–11.3 Merg/cm3, respectively, with an increase in the Mn interlayer thickness, even for the ultrathin regime of the MnGa layer. For p-MTJs showing a high TMR and PMA, electron microscopy indicated the presence of 3–4 MLs of Mn at the MnGa/MgO interface; thus, the Mn modification enhanced the TMR as well as improved the PMA. This may be a promising finding to develop a Mn-based free layer for spin-transfer-torque devices for high-recording-density magnetoresistive random access memory and a sub-THz oscillator/detector.

Structural and magnetic characterization of Mn/NiFe bilayers with ion-beam-assisted deposition

The exchange bias effect in ferromagnetic (FM)/antiferromagnetic (AF) bilayer structures has been widely investigated because its underlying principle is critical for spintronic applications. In this work, the effect of Ar+ beam bombardment on the microstructural and magnetic properties of the Mn/NiFe thin films was investigated. The in-situ Ar+ bombardment nontrivially promoted the Mn/NiFe intermixing and facilitated the formation of the FeMn phase, accompanied by a remarkable reduction of Mn and NiFe layer thickness. The enhanced Mn/NiFe intermixing greatly disordered the interfacial spins, inhibiting the interfacial exchange coupling and giving rise to a significant decrease of the exchange bias field (Hex). The facilitated Mn/NiFe intermixing effect also dramatically degraded the magnetocrystalline anisotropy of the NiFe crystallites, leading to a notable suppression of the coercivity (Hc). These results indicate that both the exchange bias and coercivity of the Mn/NiFe bilayers can be directly affected by the in-situ Ar+ bombardment, offering an effective way to modify the magnetism of the exchange-bias systems.

GaMnSb/InGaAs/GaAs heterostructure leds with a ferromagnetic injector layer

A diode structure with a p-n junction and an InGaAs/GaAs quantum well in the space-charge region and a ferromagnetic GaMnSb layer as the p-type semiconductor has been fabricated and studied. The possibility of obtaining high-efficiency electroluminescence (EL) from the structure was demonstrated. It was found that the EL efficiency depends on the growth parameters of the ferromagnetic GaMnSb layer, i.e., the Mn content and layer thickness. The possible mechanisms of EL from the diodes under study were considered. Circularly polarized EL was obtained from the structures. It was shown that the degree of polarization (0.012 in a magnetic field of 0.37 T) remains nearly invariable in the temperature range 10–50 K and the circular polarization of the emitted light is due to the injection of spin-polarized holes into the quantum well from the ferromagnetic GaMnSb layer.

Competitive role of Mn diffusion with growth in Mn catalyzed nanostructures

The use of dopant as a catalyst in the vapor-liquid-solid mode of growth offers a unique way to dope simultaneously the growing nanostructure. This paper reports the use of Mn as a catalyst to grow ZnS nanostructures and simultaneously doping it. It is also shown here that the diffusion rate of Mn in ZnS can be varied to compete with the growth rate of the nanostructures. The diffusion of Mn is found to depend strongly on the Mn layer thickness. The composition of nanowires is determined from X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) measurements. XPS revealed that Mn diffuses only on the surface forming MnS2 compound and its concentration on the surface of nanowires shows a strong dependence on its droplet size. The thermodynamic models are used to examine the interplay of the growth of ZnS nanostructures and Mn diffusion in them. The results show that uniform doping during the growth can be achieved by carefully tuning the growth temperature and the catalyst layer thickness or catalyst droplet size.

Induced ferromagnetism in Mn3N2 phase embedded in Mn/Si3N4 multilayers

Room temperature ferromagnetism has been obtained for different sets of Mn/Si3N4 multilayers prepared by sputtering. In order to find the most suitable conditions to stabilize the ferromagnetic ordering in this system, the evolution of the magnetic properties has been studied for films in which the Si3N4 layer thickness was maintained constant while that of the Mn layer was varied, [Mn(tm)/Si3N4(3.4 nm)]n, and conversely, in [Mn(0.7 nm)/Si3N4(tsn)]43 samples, in which the Mn layer thickness was kept constant while varying the Si3N4 layer thickness. Structural, compositional, electronic and magnetic characterizations have been performed by means of x-ray reflectometry, Rutherford backscattering spectrometry, x-ray photoemission spectroscopy, x-ray absorption, and superconducting quantum interference device for further knowledge of the magnetic-structural relationship in this system. Our results show that the peculiar magnetic behavior of these films is mainly related to the stabilization of a slightly distorted Mn3N2 phase that is induced by the Si3N4 at the interfaces. For samples with larger Mn layer thickness, metallic Mn and Mn3N2 phases coexist, which leads to a reduction of the total magnetization per Mn atom due to the presence of metallic Mn. For small Mn layer thickness (tm<0.86 nm), where noncontinuous Mn3N2 layers are formed, the magnetization decreases noticeably due to the superparamagnetic size limit. It has been found that the best conditions for the stabilization of the ferromagnetism in this system occur when both, the manganese-rich and the silicon nitride layers, are continuous and with similar thickness, close to 3.5 nm.

Magnetic properties of Pr–Fe–B/Mn films with perpendicular anisotropy

The influence of a Mn layer on the magnetic properties of sputtered Pr–Fe–B/Mn films with Cu spacer layer has been investigated for various Mn layer thicknesses. The Pr–Fe–B/Mn films all possess perpendicular anisotropy. An enhancement of the intrinsic coercivity i H c is observed for suitable Mn layer thickness and i H c exhibits an oscillatory dependence on the thickness of the Mn layer with a period of about 60 nm. The average size of the columnar Pr 2Fe 14B grains is about 100 nm. A highest iH c value of 22.1 kOe and an optimal ( BH) max value of 18.2 MGOe are reported for these Pr–Fe–B/Mn films.

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.

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+.

Magnetic and optical characterization of ferromagnetic [formula omitted] multilayers

We have investigated the magnetic and structural properties of Mn / SnO 2 multilayers deposited onto Si(1 0 0) substrates at room temperature using the magnetron sputtering method. The nominal Mn layer thickness ranged from 0.4 up to 10 nm. The multilayers structure was studied by X-ray and optical reflectivity. Magnetic measurements indicate the presence of two distinct contributions. One is ferromagnetic with an order temperature above 400 K for all samples and another paramagnetic. Both ferromagnetic and paramagnetic susceptibilities per Mn atom increase as the Mn layer thickness in the multilayers is reduced, corresponding to a more diluted situation. Oscillations in the optical reflectivity measurements are only observed for the sample with nominal Mn layer thickness of 0.4 nm (75 bilayers). In this case, the disappearance of the continuous Mn layers and therefore of the interfaces preserve the necessary transparency. In multilayers with thicker Mn layer, the effective absorption coefficient increases.

Ab initio calculations of transport properties of epitaxial (Ga,Mn)As systems

We calculate transport properties of thin ( Ga , Mn ) As layers sandwiched between two Cr ( 0 0 1 ) leads as a function of Mn concentration and layer thickness, special attention is paid to the spin polarization of the current-perpendicular-to-plane (CPP) conductance. We compare our results to bulk properties. Doping GaAs with Mn increases occurrence of As antisites on the Ga sublattice. Our method allows us to take into account even very small defect concentration changes, and we show that it may have a dramatic impact on the CPP spin polarization, apart from its already known influence on Curie temperatures.

Production of capacitive films from Mn thin films: Effects of current density and film thickness

Electrochemical oxidation of Mn thin films produces a highly capacitive, porous MnO 2 surface layer. The effects of current density and deposited Mn layer thickness on the morphology of the porous surface layer are quite pronounced. A higher current density results in a much thinner, finer porous layer while thicker deposited Mn films give much thicker porous films. Increasing the current density results in a film with greater hydration and an increase in capacitance. For the films of varying deposited layer thickness, oxidation occurs at a single current density and, as a result, the relative hydration of the film does not change noticeably. Increasing the deposited layer thickness results in a porous surface layer that increases in thickness, but with a constant amount of hydration. This combination of trends results in a significant increase in the areal capacitance of the film but little change in the specific capacitance.

Enhanced magnetic moments in Co/Mn multilayers: structural and magnetic investigations

The structures and magnetic properties of Co(6)/Mn( t Mn) multilayers were systematically investigated by X-ray diffractometry and SQUID magnetometry to reveal the effects of interfacial d–d hybridization on them. Increasing Mn layer thickness, the main profile in HAXRD patterns changes from a single peak for t Mn⩽7 Å to split peaks for t Mn⩾10 Å. With decreasing the temperature, the magnetization increases greatly through two magnetic transitions at the temperatures much lower than that of bulk α-Mn. At 5 K, the absolute value for the magnetization becomes unusually large. The magnetization is highly anisotropic and for t Mn⩽20 Å, the perpendicular direction is the easy magnetization axis. Correlations between the magnetization, exchange bias and coercive force are found. The high magnetization and the correlations are interpreted in terms of the direct d–d hybridization in the vicinity of Co–Mn interfaces.

Stabilisation of fcc cobalt layers by 0.4 nm thick manganese layers in Co/Mn superlattices

Epitaxial Co/Mn multilayers (0.75 to 6 nm Co, 0.4 nm Mn layer thickness) have been grown on mica substrates covered by a (0002) Ru buffer layer. The structural properties of these layers have been studied using X-ray diffraction, nuclear magnetic resonance (NMR), and high resolution transmission electron microscopy (HRTEM). The Co layers, grown as face centred cubic (fcc), were found to be stabilised by the very thin Mn layers. Data obtained using X-ray diffraction and NMR were analysed and found to be in good agreement, while Monte-Carlo simulations were used to interpret the data and calculate the expected diffracted intensity and NMR spectra. The HRTEM data show that the Mn layers give rise to a large strain contrast extending, in the growth direction, over a distance which exceeds the thickness of the Mn layers. The superlattices could be described as having an fcc structure containing randomly located stacking faults with varying densities. The results verify the presence of a dominant, almost perfect phase of fcc stacking, and of a faulted hcp phase, while the number of defects increases with the Co layer thickness.

Electroluminescent Devices with Nanostructured ZnS:Mn Emission Layer Operated at 20 V0-p

ABSTRACTWe have developed a new type of a thin-film electroluminescence (TFEL) device with nano- structured (NS)-ZnS:Mn utilizing its enhanced luminescent efficiency due to the quantum confinement (QC) effects. As NS-ZnS:Mn, ZnS:Mn/Si3N4 multilayers with thicknesses of 1.9–3.5 nm for ZnS were prepared by a rf-magnetron sputtering method. From the results of grazing incidence X-ray reflectometry and X-ray diffractmetry, formation of ZnS:Mn nanocrystals in the ZnS layers are confirmed. With a decrease in the ZnS:Mn layer thickness, the photoluminescence (PL) efficiency associated with the Mn2+ transitions is increased, and the PL excitation spectrum is shifted toward higher energies, indicating appearance of the QC effects. As the results of the application of NS-ZnS:Mn to the emission layer of the TFEL device, we have successfully observed reddish-orange emission above the threshold voltage of 12 V0-p, and the maximum luminance is 3.0 cd/m2 operated with the 1-kHz sinusoidal voltage of 20 V0-p.

Magnetic properties of Fe/bct Mn superlattices grown by molecular beam epitaxy

Fe/body-centered-tetragonal(bct) Mn superlattices on (0 0 1)-oriented Ge substrates have been prepared by molecular beam epitaxy (MBE). X-ray measurements confirm the high quality of the samples, which all show increased lattice spacing in growth direction compared with bulk bcc Fe. RHEED reflection position analysis proves a different growth behavior of the Fe/Mn and Mn/Fe interfaces. Magnetic measurements show a long period of the oscillatory exchange coupling, but no two-monolayer oscillation. Moreover, all samples show a dramatic reduction of the saturation magnetization (Ms), up to 50%, with increasing Mn layer thickness, probably due to the formation of an antiferromagnetic alloy at the Mn/Fe interface. A giant magnetoresistance (GMR) effect is observed for strong antiferromagnetically coupled Fe layers, which depends on the Mn layer thickness in the superlattice. None of the samples exhibited a ferro- or ferrimagnetic state of bct Mn.

Magnetic anisotropy of epitaxial Co/Mn superlattices: An angular-dependent ferromagnetic resonance study.

The magnetic anisotropy of epitaxial [${\mathrm{Co}}_{24\mathrm{}\mathrm{\AA{}}}$/Mn(${\mathit{t}}_{\mathrm{Mn}}$)${]}_{12}$ superlattices is studied as a function of the Mn layer thickness by means of ferromagnetic resonance. For fixed cobalt layer thickness one finds a transition from a (111) fcc to a (0001) hcp cobalt structure at a critical thickness of 10--12 \AA{} for the Mn layers. This is seen from the sharp increase of the uniaxial magnetocrystalline anisotropy from nearly zero to 2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ erg/${\mathrm{cm}}^{3}$. A similar enhancement of the perpendicular to in-plane resonance linewidth by a factor of 4 indicates a strong increase of the number of structural defects. The complete out-of-plane angular dependence of the resonance field yields the second- and fourth-order uniaxial magnetic anisotropy constants whereas that of the ferromagnetic resonance linewidth gives a measure of the magnetic homogeneity. The experimental results are well explained by a theoretical model which allows us to estimate the number of defects within the Co layers and to discuss their origin. \textcopyright{} 1996 The American Physical Society.