Fe 3 O 4 nanoparticles are one of the most promising candidates for biomedical applications such ... more Fe 3 O 4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple analytical formulae overestimate the magnetic shape anisotropy and that the underlying cubic anisotropy makes a significant contribution to the energy barrier for moderately elongated particles. Our results enable a better estimation of the effective magnetic anisotropy of highly crystalline magnetite nanoparticles and is a step towards quantitative prediction of the heating effects of magnetic nanoparticles.
In this work we present the structural and electrical characterization of sputter-deposited CoFe(... more In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling jun...
To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresist... more To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresistive random-access memory devices, the electric-field control of magnetization vectors in ferromagnetic electrodes has shown much promise. Here, we show the giant converse magnetoelectric (CME) effect in a multiferroic heterostructure consisting of the ferromagnetic Heusler alloy Co2FeSi and ferroelectric-oxide Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) for electric-field control of magnetization vectors. Using an in-plane uniaxial magnetic anisotropy of polycrystalline Co2FeSi film grown on PMN-PT(011), the nonvolatile and repeatable magnetization vector switchings in remanent states are demonstrated. The CME coupling coefficient of the polycrystalline Co2FeSi/PMN-PT(011) is over 1.0 × 10−5 s/m at room temperature, comparable to those of single-crystalline Fe1-xGax/PMN-PT systems. The giant CME effect has been demonstrated by the strain-induced variation in the magnetic anisotropy energy of Co2FeS...
We present a structural and density-functional theory study of the interface of the quasi-twin-fr... more We present a structural and density-functional theory study of the interface of the quasi-twin-free grown three-dimensional topological insulator Bi 2 Te 3 on Ge(111). Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy in combination with first-principles calculations show that the weak van der Waals adhesion between the Bi 2 Te 3 quintuple layer and Ge can be overcome by forming an additional Te layer at their interface. The first-principles calculations of the formation energy of the additional Te layer show it to be energetically favorable as a result of the strong hybridization between the Te and Ge.
We study magnetic and magnetotransport properties of an epitaxial interfacial multiferroic system... more We study magnetic and magnetotransport properties of an epitaxial interfacial multiferroic system consisting of a ferromagnetic Heusler-alloy Co 2 FeSi and a ferroelectric-oxide BaTiO 3. L2 1-ordered Co 2 FeSi epilayers on BaTiO 3 (001) show an in-plane uniaxial magnetic anisotropy with strong temperature dependence, induced by the presence of the magnetoelastic effect via the spin-orbit interaction at the Co 2 FeSi/BaTiO 3 (001) interface. In the Co 2 FeSi Hall-bar devices, the anisotropic magnetoresistance (AMR) hysteretic curves depending on inplane magnetization reversal processes on the a and c domains of BaTiO 3 (001) are clearly observed at room temperature. Notably, the magnitude of the AMR ratio (%) for Co 2 FeSi Hall-bar devices can be tuned through the a − c domain wall motion of BaTiO 3 (001) by applying electric fields. We propose that the tunable AMR effect is associated with the modulation of the spin-orbit interaction, exchange interaction, and/or the electronic band structure near the Fermi level by applying electric fields in the epitaxial Co 2 FeSi/BaTiO 3 (001) interfacial multiferroic system.
Frontiers of Chemical Science and Engineering, 2021
Here we present an economical ambient pressure drying method of preparing monolithic silica aerog... more Here we present an economical ambient pressure drying method of preparing monolithic silica aerogels from methyltrimethoxysilane precursor while using sodium bicarbonate solution as the exchanging solvent. We prepared silica aerogels with a density and a specific surface area of 0.053 g·cm−3 and 423 m2·g−1, respectively. The average pore diameter of silica aerogels is 23 nm as the pore specific volume is 1.11 cm3·g−1. Further, the contact angle between water droplet and the surface of silica aerogels in specific condition can be as high as 166°, which indicates a super-hydrophobic surface of aerogels.
Fe3O4 nanoparticles are one of the most promising candidates for biomedical applications such as ... more Fe3O4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple analytical formulae overestimate the magnetic shape anisotropy and that the underlying cubic anisotropy makes a significant contribution to the energy barrier for moderately elongated particles. Our results enable a better estimation of the effective magnetic anisotropy of highly crystalline magnetite nanoparticles and is a step towards quantitative prediction of the heating effects of magnetic na...
From simple averaging to more sophisticated registration and restoration strategies, such as supe... more From simple averaging to more sophisticated registration and restoration strategies, such as super-resolution (SR), there exist different computational techniques that use a series of images of the same object to generate enhanced images where noise and other distortions have been reduced. In this work, we provide qualitative and quantitative measurements of this enhancement for high-angle annular dark-field scanning transmission electron microscopy imaging. These images are compared in two ways, qualitatively through visual inspection in real and reciprocal space, and quantitatively, through the calculation of objective measurements, such as signal-to-noise ratio and atom column roundness. Results show that these techniques improve the quality of the images. In this paper, we use an SR methodology that allows us to take advantage of the information present in the image frames and to reliably facilitate the analysis of more difficult regions of interest in experimental images, such ...
We show a direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on ... more We show a direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on the spin transport signals in semiconductor-based lateral spin-valve (LSV) devices. Based on atomic scale Z contrast scanning transmission electron microscopy and energy dispersive x-ray spectroscopy we show that atomic order/disorder of Co2FeAl0.5Si0.5 (CFAS)/n-Ge LSV devices is critical for the spin injection in Ge. By conducting a post annealing of the LSV devices, we find 90% decrease in the spin signal while there is no difference in the electrical properties of the CFAS/n-Ge contacts and in the spin diffusion length of the n-Ge layer. We show that the reduction in the spin signals after annealing is attributed to the presence of intermixing phases at the Heusler/semiconductor interface. First principles calculations show how that intermixed interface region has drastically reduced spin polarisation at the Fermi level, which is the main cause for the significant decrease of the spin signal in the annealed devices above 300 • C.
Sustainable electric double-layer capacitor (EDLC) electrodes were made by incorporating nano-gra... more Sustainable electric double-layer capacitor (EDLC) electrodes were made by incorporating nano-graphite particles into the electrode pore walls, improving conductivity and capacitance. The combination of ball milling, microwave processing and carbonisation were key to excellent nanoparticle dispersion.
Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like ... more Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell FeO/MnFeO MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic corr...
Engineering of the atomic structure of hetero-interfaces enables tuning of electronic properties ... more Engineering of the atomic structure of hetero-interfaces enables tuning of electronic properties of the heterostructure such as band alignment, Schottky barrier height, interface conductivity and magnetism. Hence it is the aim of continuous experimental and theoretical research to control chemical intermixing arising due to interdiffusion, as well as interface strain, which are the main parameters that control the structural and chemical quality of a given heterostructure. However, tailoring the atomic structure of ferromagnet/semiconductor interfaces, of crucial importance for spintronic applications, has been shown to be a rather elusive goal despite the intensive research efforts over the past years [1, 2].
We present a structural and density functional theory study of Fe x Cu 1 − x Se within the three-... more We present a structural and density functional theory study of Fe x Cu 1 − x Se within the three-dimensional topological insulator Bi 2 Te 3. The Fe x Cu 1 − x Se inclusions are single-crystalline and epitaxially oriented with respect to the Bi 2 Te 3 thin film. Aberrationcorrected scanning transmission electron microscopy and electron energy loss spectroscopy show an atomically sharp Fe I Cu 1 − x Se/Bi 2 Te 3 interface. The Fe x Cu 1 − x Se/Bi 2 Te 3 interface is determined by Se-Te bonds and no misfit dislocations are observed, despite the different lattice symmetries and large lattice mismatch of ∼ 19%. First-principle calculations show that the large strain at the Fe x Cu 1 − x Se/Bi 2 Te 3 interface can be accommodated by van der Waals-like bonding between Se and Te atoms.
Bi 2 Se 3 is a 3D topological insulator (TI) that has attracted a lot of research interest due to... more Bi 2 Se 3 is a 3D topological insulator (TI) that has attracted a lot of research interest due to its exotic properties [1], associated with topologically-protected helical two-dimensional surface states and onedimensional bulk states associated with line defects such as dislocations. Recent theoretical studies [2] have shown that when graphene is placed near Bi 2 Se 3 the strong spin orbit interaction due to proximity effects will open the band gap in graphene for 0.2 eV. Therefore TI/graphene heterostructures are promising platform for developing electronic and spintronic graphene based devices.
By using first-principles calculations we show that the spin-polarization reverses its sign at at... more By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si–Co–Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.
We show that Co2FeAl0.5Si0.5 film deposited on Si(111) has a single crystal structure and twin re... more We show that Co2FeAl0.5Si0.5 film deposited on Si(111) has a single crystal structure and twin related epitaxial relationship with the substrate. Sub-nanometer electron energy loss spectroscopy shows that in a narrow interface region there is a mutual inter-diffusion dominated by Si and Co. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that the film has B2 ordering. The film lattice structure is unaltered even at the interface due to the substitutional nature of the intermixing. First-principles calculations performed using structural models based on the aberration corrected electron microscopy show that the increased Si incorporation in the film leads to a gradual decrease of the magnetic moment as well as significant spin-polarization reduction. These effects can have significant detrimental role on the spin injection from the Co2FeAl0.5Si0.5 film into the Si substrate, besides the structural integrity of this junction.
Fe 3 O 4 nanoparticles are one of the most promising candidates for biomedical applications such ... more Fe 3 O 4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple analytical formulae overestimate the magnetic shape anisotropy and that the underlying cubic anisotropy makes a significant contribution to the energy barrier for moderately elongated particles. Our results enable a better estimation of the effective magnetic anisotropy of highly crystalline magnetite nanoparticles and is a step towards quantitative prediction of the heating effects of magnetic nanoparticles.
In this work we present the structural and electrical characterization of sputter-deposited CoFe(... more In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling jun...
To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresist... more To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresistive random-access memory devices, the electric-field control of magnetization vectors in ferromagnetic electrodes has shown much promise. Here, we show the giant converse magnetoelectric (CME) effect in a multiferroic heterostructure consisting of the ferromagnetic Heusler alloy Co2FeSi and ferroelectric-oxide Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) for electric-field control of magnetization vectors. Using an in-plane uniaxial magnetic anisotropy of polycrystalline Co2FeSi film grown on PMN-PT(011), the nonvolatile and repeatable magnetization vector switchings in remanent states are demonstrated. The CME coupling coefficient of the polycrystalline Co2FeSi/PMN-PT(011) is over 1.0 × 10−5 s/m at room temperature, comparable to those of single-crystalline Fe1-xGax/PMN-PT systems. The giant CME effect has been demonstrated by the strain-induced variation in the magnetic anisotropy energy of Co2FeS...
We present a structural and density-functional theory study of the interface of the quasi-twin-fr... more We present a structural and density-functional theory study of the interface of the quasi-twin-free grown three-dimensional topological insulator Bi 2 Te 3 on Ge(111). Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy in combination with first-principles calculations show that the weak van der Waals adhesion between the Bi 2 Te 3 quintuple layer and Ge can be overcome by forming an additional Te layer at their interface. The first-principles calculations of the formation energy of the additional Te layer show it to be energetically favorable as a result of the strong hybridization between the Te and Ge.
We study magnetic and magnetotransport properties of an epitaxial interfacial multiferroic system... more We study magnetic and magnetotransport properties of an epitaxial interfacial multiferroic system consisting of a ferromagnetic Heusler-alloy Co 2 FeSi and a ferroelectric-oxide BaTiO 3. L2 1-ordered Co 2 FeSi epilayers on BaTiO 3 (001) show an in-plane uniaxial magnetic anisotropy with strong temperature dependence, induced by the presence of the magnetoelastic effect via the spin-orbit interaction at the Co 2 FeSi/BaTiO 3 (001) interface. In the Co 2 FeSi Hall-bar devices, the anisotropic magnetoresistance (AMR) hysteretic curves depending on inplane magnetization reversal processes on the a and c domains of BaTiO 3 (001) are clearly observed at room temperature. Notably, the magnitude of the AMR ratio (%) for Co 2 FeSi Hall-bar devices can be tuned through the a − c domain wall motion of BaTiO 3 (001) by applying electric fields. We propose that the tunable AMR effect is associated with the modulation of the spin-orbit interaction, exchange interaction, and/or the electronic band structure near the Fermi level by applying electric fields in the epitaxial Co 2 FeSi/BaTiO 3 (001) interfacial multiferroic system.
Frontiers of Chemical Science and Engineering, 2021
Here we present an economical ambient pressure drying method of preparing monolithic silica aerog... more Here we present an economical ambient pressure drying method of preparing monolithic silica aerogels from methyltrimethoxysilane precursor while using sodium bicarbonate solution as the exchanging solvent. We prepared silica aerogels with a density and a specific surface area of 0.053 g·cm−3 and 423 m2·g−1, respectively. The average pore diameter of silica aerogels is 23 nm as the pore specific volume is 1.11 cm3·g−1. Further, the contact angle between water droplet and the surface of silica aerogels in specific condition can be as high as 166°, which indicates a super-hydrophobic surface of aerogels.
Fe3O4 nanoparticles are one of the most promising candidates for biomedical applications such as ... more Fe3O4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple analytical formulae overestimate the magnetic shape anisotropy and that the underlying cubic anisotropy makes a significant contribution to the energy barrier for moderately elongated particles. Our results enable a better estimation of the effective magnetic anisotropy of highly crystalline magnetite nanoparticles and is a step towards quantitative prediction of the heating effects of magnetic na...
From simple averaging to more sophisticated registration and restoration strategies, such as supe... more From simple averaging to more sophisticated registration and restoration strategies, such as super-resolution (SR), there exist different computational techniques that use a series of images of the same object to generate enhanced images where noise and other distortions have been reduced. In this work, we provide qualitative and quantitative measurements of this enhancement for high-angle annular dark-field scanning transmission electron microscopy imaging. These images are compared in two ways, qualitatively through visual inspection in real and reciprocal space, and quantitatively, through the calculation of objective measurements, such as signal-to-noise ratio and atom column roundness. Results show that these techniques improve the quality of the images. In this paper, we use an SR methodology that allows us to take advantage of the information present in the image frames and to reliably facilitate the analysis of more difficult regions of interest in experimental images, such ...
We show a direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on ... more We show a direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on the spin transport signals in semiconductor-based lateral spin-valve (LSV) devices. Based on atomic scale Z contrast scanning transmission electron microscopy and energy dispersive x-ray spectroscopy we show that atomic order/disorder of Co2FeAl0.5Si0.5 (CFAS)/n-Ge LSV devices is critical for the spin injection in Ge. By conducting a post annealing of the LSV devices, we find 90% decrease in the spin signal while there is no difference in the electrical properties of the CFAS/n-Ge contacts and in the spin diffusion length of the n-Ge layer. We show that the reduction in the spin signals after annealing is attributed to the presence of intermixing phases at the Heusler/semiconductor interface. First principles calculations show how that intermixed interface region has drastically reduced spin polarisation at the Fermi level, which is the main cause for the significant decrease of the spin signal in the annealed devices above 300 • C.
Sustainable electric double-layer capacitor (EDLC) electrodes were made by incorporating nano-gra... more Sustainable electric double-layer capacitor (EDLC) electrodes were made by incorporating nano-graphite particles into the electrode pore walls, improving conductivity and capacitance. The combination of ball milling, microwave processing and carbonisation were key to excellent nanoparticle dispersion.
Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like ... more Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell FeO/MnFeO MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic corr...
Engineering of the atomic structure of hetero-interfaces enables tuning of electronic properties ... more Engineering of the atomic structure of hetero-interfaces enables tuning of electronic properties of the heterostructure such as band alignment, Schottky barrier height, interface conductivity and magnetism. Hence it is the aim of continuous experimental and theoretical research to control chemical intermixing arising due to interdiffusion, as well as interface strain, which are the main parameters that control the structural and chemical quality of a given heterostructure. However, tailoring the atomic structure of ferromagnet/semiconductor interfaces, of crucial importance for spintronic applications, has been shown to be a rather elusive goal despite the intensive research efforts over the past years [1, 2].
We present a structural and density functional theory study of Fe x Cu 1 − x Se within the three-... more We present a structural and density functional theory study of Fe x Cu 1 − x Se within the three-dimensional topological insulator Bi 2 Te 3. The Fe x Cu 1 − x Se inclusions are single-crystalline and epitaxially oriented with respect to the Bi 2 Te 3 thin film. Aberrationcorrected scanning transmission electron microscopy and electron energy loss spectroscopy show an atomically sharp Fe I Cu 1 − x Se/Bi 2 Te 3 interface. The Fe x Cu 1 − x Se/Bi 2 Te 3 interface is determined by Se-Te bonds and no misfit dislocations are observed, despite the different lattice symmetries and large lattice mismatch of ∼ 19%. First-principle calculations show that the large strain at the Fe x Cu 1 − x Se/Bi 2 Te 3 interface can be accommodated by van der Waals-like bonding between Se and Te atoms.
Bi 2 Se 3 is a 3D topological insulator (TI) that has attracted a lot of research interest due to... more Bi 2 Se 3 is a 3D topological insulator (TI) that has attracted a lot of research interest due to its exotic properties [1], associated with topologically-protected helical two-dimensional surface states and onedimensional bulk states associated with line defects such as dislocations. Recent theoretical studies [2] have shown that when graphene is placed near Bi 2 Se 3 the strong spin orbit interaction due to proximity effects will open the band gap in graphene for 0.2 eV. Therefore TI/graphene heterostructures are promising platform for developing electronic and spintronic graphene based devices.
By using first-principles calculations we show that the spin-polarization reverses its sign at at... more By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si–Co–Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.
We show that Co2FeAl0.5Si0.5 film deposited on Si(111) has a single crystal structure and twin re... more We show that Co2FeAl0.5Si0.5 film deposited on Si(111) has a single crystal structure and twin related epitaxial relationship with the substrate. Sub-nanometer electron energy loss spectroscopy shows that in a narrow interface region there is a mutual inter-diffusion dominated by Si and Co. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that the film has B2 ordering. The film lattice structure is unaltered even at the interface due to the substitutional nature of the intermixing. First-principles calculations performed using structural models based on the aberration corrected electron microscopy show that the increased Si incorporation in the film leads to a gradual decrease of the magnetic moment as well as significant spin-polarization reduction. These effects can have significant detrimental role on the spin injection from the Co2FeAl0.5Si0.5 film into the Si substrate, besides the structural integrity of this junction.
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Papers by Vlado Lazarov