Magnetite Thin Films Research Articles

Atomic origin of magnetic coupling of antiphase boundaries in magnetite thin films

Revealing the magnetic coupling nature of boundary defects is crucial for in-depth understanding of the behavior and properties of magnetic materials and devices. Here, magnetite (i.e., Fe3O4) thin films were grown epitaxially on (100) SrTiO3 single-crystal substrates by pulsed laser deposition. Atomic-scale scanning transmission electron microscopy characterizations reveal that three types of antiphase boundaries (APBs) are formed in the Fe3O4 thin film. They are the (100) APB that is formed on the (100) plane with a crystal translation of (1/4)a[011¯], the type I and type II (110) APBs that are both formed on the (110) plane with the same crystal translation of (1/4)a[101] but different terminated atomic planes. The type I (110) APB is terminated at the atomic plane with mixed tetrahedral- and octahedral-sites Fe atoms, the type II (110) APB is terminated at the octahedral-site Fe plane. First-principles calculations reveal that the (100) APB and the type I (110) APB tend to form the ferromagnetic coupling that will not decrease the spin polarization of Fe3O4 films, while the type II (110) APB prefers to form the antiferromagnetic coupling that will degrade the magnetic properties. The magnetic coupling modes of the APBs are closely related to the Fe-O-Fe bond angles across the boundaries.

Calculated Lattice Thermal Conductivity of Magnetite Thin Films based on Modified Callaway Model

Thermal conductivity is an important parameter for semiconductor materials used in the nanoscale applications. In this study, the lattice thermal conductivity (LTC) of magnetite thin films was simulated by Modified Callaway Model. To fit the experimental data, some quantities, such as mean bond length, the lattice constant, and volume per atom were calculated. Also, the model is based on some other quantities, such as gruneisen parameter, electron concentration, and surface roughness that were found through fitting theoretical with experimental LTC. As a result, this model could work comparably well in all sizes, and the relationship between the fitting parameters and the thickness of the magnetite films was estimated.

Characterization and In Vitro Studies of Low Reflective Magnetite (Fe3O4) Thin Film on Stainless Steel 420A Developed by Chemical Method

Stainless steel has been the most demanded material for surgical utensil manufacture due to superior mechanical properties, sufficient wear, and corrosion resistance. Surgical grade 420A stainless steel is extensively used for producing sophisticated surgical instruments. Since these instruments are used under bright light conditions prevalent in operation theatres, the reflection from the material is significant which causes considerable strain to the eye of the surgeon. Surgical instruments with lower reflectance will be more efficient under these conditions. A low reflective thin -film coating has often been suggested to alleviate this inadmissible difficulty. This paper reports the development of an optimum parametric low reflective magnetite coating on the surface of SS 420A with a black color using chemical hot alkaline conversion coating technique and its bioactivity studies. Coating process parameters such as coating time, bath temperature, and chemical composition of bath are optimized using Taguchi optimization techniques. X-ray photoelectron spectroscopy (XPS) analysis was used to identify the composition of elements and the chemical condition of the developed coating. Surface morphological studies were accomplished with a scanning electron microscope (SEM). When coupled with an energy-dispersive X-ray analysis (EDAX), compositional information can also be collected simultaneously. Invitro cytotoxicity tests, corrosion behavior, the effect of sterilization temperature on adhesion property, and average percentage reflectance (R) of the developed coating have also been evaluated. These results suggest adopting the procedure for producing low reflective conversion coatings on minimally invasive surgical instruments produced from medical grade 420A stainless steel.

Elucidation of Gas Formation Effect on Strong Inhibition of Magnetite Dissolution in Cu2S Through In-Situ Analysis of Reactive Interface

During copper smelting using a flash furnace, the solid magnetite (Fe3O4) phase that stagnates at the slag/matte interface inhibits the absorption of the suspended matte in the slag into the matte, resulting in copper loss. However, the phenomena that occur at the magnetite/matte interface are complex, and the effect of gas formation at the interface on the removal of magnetite has not been studied. In this study, we elucidated the effect of gas formation on the dissolution of the magnetite phase into the matte by directly observing the high-temperature reaction interface through the magnetite thin film. In contrast to the rapid dissolution of magnetite into FeS in the absence of gas formation, magnetite dissolution was strongly inhibited at the Cu2S/magnetite interface by the generation, agglomeration, and accumulation of SO2 gas bubbles. A quantitative analysis of the dissolution rate of the magnetite phase into Cu2S indicated that the mass transfer rate of Fe in the matte is extremely low. We also discuss the contribution of the generated SO2 gas to the inhibition of the interfacial reaction.

Modulating the Verwey Transition of Epitaxial Magnetite Thin Films by Ionic Gating

AbstractUnderstanding the Verwey transition in magnetite (Fe3O4), a strongly correlated magnetic oxide, is a one‐century‐old topic that recaptures great attention because of the recent spectroscopy studies revealing its orbital details. Here, the modulation of the Verwey transition by tuning the orbital configurations with ionic gating is reported. In epitaxial magnetite thin films, the insulating Verwey state can be tuned continuously to be metallic showing that the low‐temperature trimeron states can be controllably metalized by both the gate‐induced oxygen vacancies and proton doping. The ionic gating can also reverse the sign of the anomalous Hall coefficient, indicating that the metallization is associated with the presence of a new type of carrier with competing spin. The variable spin orientation associated with the sign reversal is originated from the structural distortions driven by the gate‐induced oxygen vacancies.

Epitaxial lift-off of flexible single-crystal magnetite thin films with tunable magnetic performances by mechanical deformation

Integrating magnetic oxide thin films without restriction of substrates is crucial for their applications in electronic and spintronic devices. Here the water-soluble Sr3Al2O6 (SAO) layer is employed as the sacrificial layer to transfer the millimeter-size single-crystal Fe3O4 films from SrTiO3 (STO) to silicon and flexible PET substrates. Structural characterizations indicate that the transferred films have the same epitaxial quality with the as-grown films. The hysteresis loops measurements of flexible Fe3O4/PET samples show a deceasing magnetic anisotropy under both of convex and concave deformations. Such tunable magnetic anisotropy is confirmed by fitting the angular dependence of ferromagnetic resonance (FMR) fields. These results provide a damage-free way to fabricate single-crystal spinel ferrites films on the selected substrates for flexible spintronic devices.

Role of anti-phase boundaries in the formation of magnetic domains in magnetite thin films

Anti-phase boundaries (APBs) are structural defects which have been shown to be responsible for the anomalous magnetic behavior observed in different nanostructures. Understanding their properties is crucial in order to use them to tune the properties of magnetic materials by growing APBs in a controlled way since their density strongly depends on the synthesis method. In this work we investigate their influence on magnetite (Fe3O4) thin films by considering an atomistic spin model, focussing our study on the role that the exchange interactions play across the APB interface. We conclude that the main atypical features reported experimentally in this material are well described by the model we propose here, confirming the new exchange interactions created in the APB as the responsible for this deviation from bulk properties.

Large spin-dependent tunneling magnetoresistance in Fe3O4/PET heterostructures developed at room temperature: A promising candidate for flexible and wearable spintronics

Half-metallic nanocrystalline magnetite (Fe3O4) thin films, with different thicknesses were developed on polyethylene-terephthalate (PET) substrates, by reactive sputtering at room temperature. Fe3O4 film (200-nm thick)/PET heterostructures possess superior electrical and magnetic characteristics, with a Verwey transition temperature (Tv) of ~122 K and a saturation magnetization (Ms) ~ 361 emu/cm3. Furthermore, the antiferromagnetic (AFM)-coupled antiphase boundaries (APBs) controlled the transport properties of the Fe3O4 thin films, due to the tunneling of spin-polarized electrons through the films. Very-high magnetoresistance (MR) value (−8.9%) were observed for H‖Film plane, constructed from Fe3O4 (200-nm thick)/PET when H values were below 60 kOe at 300 K. In addition, flexibility tests, to examine resistivity, M-H and MR, were performed using with 90° and 45° bent angles and cyclability experiments were implemented to validate the reproducibility of these characteristics. These outcomes demonstrated that Fe3O4/PET heterostructures may represent a promising candidate for flexible/wearable spintronics.

The local structure around Ge atoms in Ge-doped magnetite thin films

AbstractDistribution of Ge atoms between tetrahedral and octahedral sites in the spinel-type structure of Fe2.64Ge0.36O4thin films fabricated by radio frequency sputtering with a composite target of magnetite and Ge has been investigated by extended X-ray absorption fine structure analysis. The local structural changes around the Ge atoms in the films induced by annealing at 573 and 873 K are discussed through comparison of the local structure for sintered crystalline Fe2.7Ge0.3O4in which Ge atoms preferentially located at the tetrahedral site of the spinel-type structure. This work provides successful information on the structural change with magnetic property of the thin films as follows: the Ge atoms statistically distributed at the tetrahedral and octahedral sites of the as-synthesized films and preferentially occupied the tetrahedral site by annealing at 873 K corresponding to the increase in magnetization.

Room-Temperature Manipulation of Magnetization Angle, Achieved with an All-Solid-State Redox Device.

An all-solid-state redox device, composed of magnetite (Fe3O4) thin film and Li+ conducting electrolyte thin film, was fabricated for the manipulation of a magnetization angle at room temperature (RT). This is a key technology for the creation of efficient spintronics devices, but has not yet been achieved at RT by other carrier doping methods. Variations in magnetization angle and magnetic stability were precisely tracked through the use of planar Hall measurements at RT. The magnetization angle was reversibly manipulated at 10° by maintaining magnetic stability. Meanwhile, the manipulatable angle reached 56°, although the manipulation became irreversible when the magnetic stability was reduced. This large manipulation of magnetic angle was achieved through tuning of the 3d electron number and modulation of the internal strain in the Fe3O4 due to the insertion of high-density Li+ (approximately 1021 cm-3). This RT manipulation is applicable to highly integrated spintronics devices due to its simple structure and low electric power consumption.

Magnetite thin films grown on different flexible polymer substrates at room temperature: Role of antiphase boundaries in electrical and magnetic properties

Currently, there is an enormous need for flexible electronic devices given their astonishing competencies. In this view, we investigated the structural, electrical, and magnetic characterstics of magnetite (Fe3O4) thin films with a thickness of 100 nm prepared using a reactive RF sputtering technique at 300 K on polycarbonate (PC), polymethyl methacrylate (PMMA), and polythene terephthalate (PET) flexible substrates. The structural properties showed that the films grown on PC, PMMA, and PET substrates exhibited the pure form of Fe3O4 nanostructures by flowing oxygen with a flow rate of 3.5 sccm. The Verwey transition temperatures (Tv) of ∼123 K, ∼124 K, and ∼126 K; saturation magnetization (Ms) values of ∼220 emu/cm3, ∼235 emu/cm3, and ∼261 emu/cm3; and magnetoresistance (MR) values of −7.1%, −7.3%, and −7.8% under the H∥Film plane below 60 kOe at 300 K for 100-nm-thick Fe3O4 film on PC, PMMA, and PET substrates respectively were observed. These remarkable results were interpreted and the effect of antiferromagnetically (AFM) coupled antiphase boundaries (APBs) was explained, which suggested that Fe3O4/PET heterostructure can be a most promising component for flexible spintronics.

마그네타이트 절연막을 가진 철압분 코어의 특성

마그네타이트 절연막을 가진 철압분 코어의 특성

Probing the local distortion of Fe sites in Fe3O4 thin films using enhanced symmetry selection in XMLD

Magnetite (${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) thin-films are among the most stimulating systems for electronic applications, in particular given that their electric and magnetic properties can be controlled by substrate strain. Here we investigate the electronic structure of a 38 nm ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}/{\mathrm{SrTiO}}_{3}\phantom{\rule{4pt}{0ex}}(001)$ thin-film by a unique set of x-ray magnetic linear dichroism (XMLD) measurements. We show that it is only possible to uncover the orbital character of the Fe sites in ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ by a systematic analysis of the XMLD angular distribution. The local symmetry of the ${\mathrm{Fe}}^{2+}$ B site in the thin-film is found to be trigonally distorted. Our results highlight that the combination of state-of-the-art XMLD measurements and theoretical simulations is indispensable for investigating the electronic structure of oxide thin-films and heterostructures.

Efficiency evaluation of the transverse magneto-optical Kerr effect in magnetoplasmonic structures

In this study the new approach to the efficiency evaluation of the transverse magneto-optical Kerr effect is considered. To assess the prospects for the practical use of structures based on TMOKE, the Figure of Merit (FOM) parameter is introduced, which is the product of the reflected/transmitted light intensity and the Kerr signal of the structure. Kerr signal defined as absolute value of the difference of light intensities at opposite magnetizations. It is shown that parameter Figure of Merit (FOM) in proposed form can give more information than the most commonly used relative value of TMOKE. The advantages of the introduced parameter are demonstrated on the example of a magnetoplasmonic structure with thin magnetite films.

Transverse magneto-optical Kerr effect in magnetoplasmonic waveguide structures based on Fe3O4

In this study transverse magneto-optical Kerr effect in transmission for the magnetite thin film with gold grating on top was examined theoretically and experimentally. The magnetite films with thickness of 200 nm were fabricated by the laser electrodispersion technique. Arrays of gold stripes with 600 nm period and 350 nm and 500 nm stripe widths were created by lift-off e-beam lithography. It was shown experimentally that the TMOKE enhancement in structures with 350 nm width is attributed to SPP excitation on gold-magnetite surface. TMOKE value δ reaches magnitude of ±5·10−3 at the wavelengths 790 nm and 860 nm at light incidence angles of 8-10° and 12-13°, respectively. In case of 500 nm stripe width, SPP excitation is poor, however δ reaches magnitude of ±6.6·10−3 at angles of incidence more than 20°, that can be associated with the quasiguided mode resonance in such structure.

Decoding Biomineralization: Interaction of a Mad10-Derived Peptide with Magnetite Thin Films.

Protein-surface interactions play a pivotal role in processes as diverse as biomineralization, biofouling, and the cellular response to medical implants. In biomineralization processes, biomacromolecules control mineral deposition and architecture via complex and often unknown mechanisms. For studying these mechanisms, the formation of magnetite nanoparticles in magnetotactic bacteria has become an excellent model system. Most interestingly, nanoparticle morphologies have been discovered that defy crystallographic rules (e.g., in the species Desulfamplus magnetovallimortis strain BW-1). In certain conditions, this strain mineralizes bullet-shaped magnetite nanoparticles, which exhibit defined (111) crystal faces and are elongated along the [100] direction. We hypothesize that surface-specific protein interactions break the nanoparticle symmetry, inhibiting the growth of certain crystal faces and thereby favoring the growth of others. Screening the genome of BW-1, we identified Mad10 (Magnetosome-associated deep-branching) as a potential magnetite-binding protein. Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we show that a Mad10-derived peptide, which represents the most conserved region of Mad10, binds strongly to (100)- and (111)-oriented single-crystalline magnetite thin films. The peptide-magnetite interaction is thus material- but not crystal-face-specific. It is characterized by broad rupture force distributions that do not depend on the retraction speed of the AFM cantilever. To account for these experimental findings, we introduce a three-state model that incorporates fast rebinding. The model suggests that the peptide-surface interaction is strong in the absence of load, which is a direct result of this fast rebinding process. Overall, our study sheds light on the kinetic nature of peptide-surface interactions and introduces a new magnetite-binding peptide with potential use as a functional coating for magnetite nanoparticles in biotechnological and biomedical applications.

Crystal texture-dependent magnetic and magnetotransport properties of half-metallic Fe3O4 films grown on oxidized Si substrates by reactive deposition

Nanocrystalline magnetite (Fe3O4) films with various preferred crystallite orientations were grown on oxidized silicon surface by reactive iron deposition in an oxygen atmosphere. Depending on the partial pressure of oxygen (PO2), the evolution of the structural, magnetic, and magnetotransport properties of the grown films was investigated. We found that the growth of films containing only the Fe3O4 phase occurs in a certain PO2 range, and the magnetite crystallites may have (311) or (110) preferred orientation. It was revealed that films with (311) and (110) textures have a column structure. An increase in the PO2 leads to a structure transformation from (311) to (110) texture with larger crystallites. A film with (110) texture showed higher values of saturation magnetization, magnetoresistance and spin polarization. The analysis of approach to magnetic saturation revealed that the local magnetic anisotropy of crystallites in textured films is much higher than the anisotropy of bulk magnetite due to the large surface contribution. The FORC diagram method in combination with the approach to magnetic saturation proved the existence of the exchange coupling between large and small grains. Our results open the reliable route for crystal texture-depending manipulation of functional properties of thin magnetite films for advanced spintronic applications.

Studies of electrical and magnetic properties across the Verwey transition in epitaxial magnetite thin films

The magnetic and transport properties of magnetite (Fe3O4) films grown on isostructural substrates (MgAl2O4, MgGa2O4, and CoGa2O4), with varying degrees of lattice mismatches (3.8%, −1.4%, and −0.8%, respectively), have been investigated. A significant reduction in the density of antiphase boundary defects is observed for the Fe3O4 films grown under optimal process conditions on smaller lattice mismatch substrates (MgGa2O4 and CoGa2O4) as compared to MgAl2O4. Correspondingly, films on these substrates show much improved magnetic properties and sharper transition in the resistance values at the Verwey transition. Room temperature magnetic hysteresis and ferromagnetic resonance measurement studies indicate the presence of uniaxial magnetic anisotropy induced by substrate-induced strain in the film. Temperature-dependent transport measurements confirm that film thickness has a larger effect on the sharpness of the Verwey transition temperature than the degree of lattice mismatch with substrates.

HAADF-STEM Image Resolution Enhancement Using High-Quality Image Reconstruction Techniques: Case of the Fe3O4(111) Surface.

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 as surfaces and interfaces. By acquiring a series of cross-sectional experimental images of magnetite (Fe3O4) thin films (111), we have generated interpolated images using averaging and SR, and reconstructed the atomic structure of the very top surface layer that consists of a full monolayer of Fe, with topmost Fe atoms in tetrahedrally coordinated sites.

The Effect of the Superlattice on the Magnetic and Transport Properties of Epitaxial Magnetite Thin Films

The surface structural, transport, and magnetic properties of superlattice films were examined, focusing on the effects of the superlattice periodicity of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO) layers. The superlattice structures of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO)n ultrathin films were fabricated using molecular-beam epitaxy on MgO(001) substrates, where n is the number of layers. It was observed that these oxide films have a single crystalline quality with the same orientation as the substrates for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as thin as approximately three unit cells. The transport and magnetic results showed that the conductivity and magnetization of the superlattice increase as the number of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO) layers is increased. Furthermore, a sharp Verwey transition was found in the (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO)n superlattices with thickness layer smaller than seen in an earlier study for a single or superlattice film. These results give the indication that Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> superlattice ultrathin films have better properties than single layers of the same thickness. This artificial growth of superlattice ultrathin films will provide a useful method to realize novel properties for other complex oxide systems.