Magnetic Films Research Articles

Experimental Techniques for the Characterization of Magnetic Thin Films

This review article describes the various experimental techniques, which are required for the characterization of magnetic thin films. Characterization is an essential process to understand the properties of magnetic thin films. By knowing the properties of these materials, one can utilize them in various technological applications as per requirements. There are different characterization tools to study the different properties of nanostructured materials. Some important experimental techniques employed to characterize the magnetic thin films are: X-Ray Diffraction, X-Ray reflectivity, Field emission scanning electron microscopy, Energy dispersive spectrometer, Transmission electron microscopy, Superconducting quantum interference device, Raman spectroscopy and X-ray absorption spectroscopy etc. These techniques will develop a better understanding of the structural, morphological, and magnetic properties of the materials to the scientific community. The discussion made in the present review article would be extremely helpful to the researchers who are doing research in the various branches of science and engineering.

Lateral semiconductor magnonics: an array of GaAs stripes atop the YIG layer

In this work, we demonstrate the numerical and experimental research of the spin-wave transport in a structure composed of a gallium arsenide (GaAs) stripe lattice interfaced to an yttrium iron garnet layer. We show that this structure can be considered as an array of an infinite number of laterally coupled ferrite-semiconductor waveguides. We show that the surface wave properties for colinear propagation along the semiconductor stripes are similar to the waves in magnetic films with partial metallization. In addition, the properties of these surface waves depend on the electron concentration of the GaAs and thus may be tuned. With regard to the wave propagation at a certain angle to the GaAs stripe lattice, the Bragg resonance forms and the corresponding band gap depend on the angle between the wave to the stripes and on the GaAs electron density. The Brillouin light scattering technique was used to experimentally observe the spin-wave beam transformation, and microwave measurements support the numerical data and reveal the mechanism of the dip formation and widening of the frequency range in the spin-wave transmission. The proposed structure could be used as a reconfigurable metasurface and magnonic beam separation unit.

Microwave magnonic micro-oscillator based on a nm-thick YIG film

A numerical model describing a magnonic active ring oscillator (MARO) based on a microscopic spin-wave delay line is proposed. The model considers excitation, propagation, and reception of the magnetostatic surface waves in a yttrium iron garnet (YIG) magnetic film with a thickness in the nanometer range. The waves are excited and received with a microscopic coplanar antenna. We employed the model to analyze the influence of the YIG-film thickness and the distance between the antennas on the MARO performance characteristics. We showed that an increase in the delay time inserted by the delay line reduces the phase noise of the MARO and increases the auto-oscillation threshold. In addition, we found a relation between the auto-oscillation threshold, the thickness of the YIG film, and the distance between the antennas. The relation helps design miniature MAROs and suggests a way to reduce the phase noise of the device. The model predicts a phase noise level of −115 dBc/Hz at a 10 kHz offset from an oscillation frequency in the vicinity of 5 GHz for the MARO based on a 100 nm-thick YIG film and 56 μm of distance between the coplanar nano-antennas of the YIG-film based delay line. We believe that this is a clear way forward to microminiaturize the time-delay feedback microwave auto-oscillators. A further reduction in the phase noise down to −125 dBc/Hz at a 10 kHz offset is found in a model of cascaded connection of several microscopic spin-wave delay lines.

Continuous strain-mediated perpendicular magnetic anisotropy in epitaxial (111) CoFe2O4 thin films grown on LiTaO3 substrates

Perpendicular magnetic anisotropy (PMA) in magnetic thin films has attracted much attention due to its potential applications in spintronics devices. Here, we report the continuous strain-mediated PMA in epitaxial (111) CoFe2O4 (CFO) thin films grown on (0001) LiTaO3 substrates. A large variation in lattice strain (∼0.9%) in a continuous way is realized in the CFO thin films by changing substrate temperature during deposition due to the difference in the thermal expansion coefficient between CFO and LiTaO3. As a result, the PMA of the (111) CFO thin films can be continuously mediated by the strain with uniaxial magnetic anisotropy energy in the range of 0.12-14.69×106 erg/cm3. Furthermore, the strain as well as the consequent PMA in the (111) CFO thin films can be maintained within the thickness of 25–205 nm, which is consistent with the scenario of the magnetoelastic effect. Our results reveal that the CFO/LiTaO3 system can be regarded as an ideal platform to realize robust PMA and its continuous strain tuning in the (111) CFO thin films by virtue of strain-induced magnetic anisotropy.

Modeling of Magnetic Films: A Scientific Perspective.

Magnetic thin-film modeling stands as a dynamic nexus of scientific inquiry and technological advancement, poised at the vanguard of materials science exploration. Leveraging a diverse suite of computational methodologies, including Monte Carlo simulations and molecular dynamics, researchers meticulously dissect the intricate interplay governing magnetism and thin-film growth across heterogeneous substrates. Recent strides, notably in multiscale modeling and machine learning paradigms, have engendered a paradigm shift in predictive capabilities, facilitating a nuanced understanding of thin-film dynamics spanning disparate spatiotemporal regimes. This interdisciplinary synergy, complemented by avantgarde experimental modalities such as in situ microscopy, promises a tapestry of transformative advancements in magnetic materials with far-reaching implications across multifaceted domains including magnetic data storage, spintronics, and magnetic sensing technologies. The confluence of computational modeling and experimental validation heralds a new era of scientific rigor, affording unparalleled insights into the real-time dynamics of magnetic films and bolstering the fidelity of predictive models. As researchers chart an ambitiously uncharted trajectory, the burgeoning realm of magnetic thin-film modeling burgeons with promise, poised to unlock novel paradigms in materials science and engineering. Through this intricate nexus of theoretical elucidation and empirical validation, magnetic thin-film modeling heralds a future replete with innovation, catalyzing a renaissance in technological possibilities across diverse industrial landscapes.

Reciprocal and non-reciprocal electromagnetic wave propagation in sub-100 nm epitaxial YIG thin films deposited under different oxygen growth pressure

Directional dependent transport of information in magnetic thin films offers a great opportunity to realize reciprocal and nonreciprocal microwave devices, such as filters, phase shifter, isolators and circulators. Electromagnetic wave (EM) propagation in sub-100 nm thin magnetic film is critical, yet reciprocal and non-reciprocal wave propagation and its accurate measurements remain a challenge. We investigated reciprocal and non-reciprocal wave propagation in 90 nm thick epitaxial thin films of yttrium iron garnet (Y3Fe5O12:YIG) grown by pulse laser deposition (PLD) technique on gadolinium gallium garnet [GGG(100)] substrates. The effect of oxygen growth pressure during deposition of YIG films exhibit directional dependence properties of electromagnetic wave propagation. The reciprocal EM wave propagation was generated by a S-type transmission line to achieve microwave (RF) magnetic fields (hRF) perpendicular to applied dc magnetic fields (HDC), to ensure the ferromagnetic resonance (FMR) condition. The center frequency is tuned up to 20 GHz with an applied magnetic field of 6 kOe. The tuning of the center frequency was achieved as of 85.3 % with HDC of 6 kOe. To achieve non-reciprocal EM-wave propagation one straight microstrip line was used to ensures a parallel configuration (parallel pumping FMR condition) of hRF to HDC. The nonreciprocity observed is due to the presence of gyrotropic properties in the YIG thin films and it enhances when YIG film was placed in asymmetric geometry. Further, oxygen growth pressure (>0.1 mbar) grown YIG films enhances the nonreciprocity by 21.6 %. The experimental results were successfully validated using high-frequency structure simulator (HFSS). Hence, these results indicate that controlled deposition parameters can be a crucial parameter in the design of reciprocal and nonreciprocal microwave signal processing devices.

Skyrmion based universal logic gates and computation operation

Swirling spin configurations with a non-trivial topological state are popularly known as magnetic skyrmions. They are often observed in magnetic thin films with perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction (DMI). Due to their small size and non-collinear spin texture, they are being considered as a potential candidate for spintronic devices such as data storage devices, and logic-based devices. These skyrmions have distinct properties and interactions, that can be utilized to control their movement by applying an external electric current. In this work, we have successfully demonstrated the operation of skyrmion-based universal NAND and NOR logic gates. We have further performed arithmetic addition of two and three single-bit by using a half and full adder, fabricated based on the XOR and AND gates. We have observed that the presence of only uniform DMI is not enough to achieve all logic operations. The presence of a negative DMI at the edges is crucial in achieving proper logic operations. The findings are very important for the realization of skyrmion-based logic and computational operations.

Polyethyleneimine-functionalized magnetic sugarcane bagasse cellulose film for the efficient adsorption of ibuprofen

Polyethyleneimine-modified magnetic sugarcane bagasse cellulose film (P-SBC/Fe3O4 film) was simply fabricated for the removal of ibuprofen (IBP), a typical emerging organic contaminant. The P-SBC/Fe3O4 film exhibited an equilibrium adsorption amount of 370.52 mg/g for IBP and a corresponding removal efficiency of 92.63 % under following adsorption conditions: 318 K, pH 4, and 0.25 mg/mL dosage. Thermodynamic studies indicated that adsorption of IBP on the P-SBC/Fe3O4 film was spontaneous (∆G < 0) and endothermic (∆H > 0). The adsorption data conformed to the Freundlich isotherm model and multilayer adsorption model (two layers), and an average of 3–4 active sites on the P-SBC/Fe3O4 film share an IBP molecule. Both the EDR-IDR and AOAS models vividly described the dynamic characteristics of adsorption process. Model fitting results, theoretical calculations, and comprehensive characterization revealed that adsorption is driven by electrostatic interactions between the primary amine of P-SBC/Fe3O4 film and the carboxyl group of IBP molecule, while other weak interactions are also non-ignorable. Furthermore, quantitative calculations based on density functional theory (DFT) underscored the importance of PEI functionalization. In conclusion, P-SBC/Fe3O4 film is an environmentally friendly and cost-effective adsorbent with significant potential for effectively removing IBP, while maintaining its efficacy over multiple cycles.

Contribution of surface scattering to the GMR effect in the magnetic multilayer films

Contribution of surface scattering to the GMR effect in the magnetic multilayer films

Berry curvature derived negative magnetoconductivity observed in type-II magnetic Weyl semimetal films

Berry curvature derived negative magnetoconductivity observed in type-II magnetic Weyl semimetal films

Navigating the magnetic contribution of the commonly used single-crystal substrates SrTiO3 (100) and LaAlO3 (100) in weak magnetic thin films

In recent years, thin films of weak ferromagnetic materials have been in huge demand; however, probing their magnetic characteristics has been difficult due to contributions from underlying substrates. In the present study, we have analyzed the magnetic properties of the commonly used single-crystal SrTiO3 (100) and LaAlO3 (100) substrates and performed a time-dependent annealing protocol in vacuum and ambient oxygen pressure to mitigate the intrinsic weak ferromagnetic contributions from these substrates arising due to the presence of disorder or defects such as vacancies in the pristine substrates. It is shown that after proper air annealing, the substrate magnetic background becomes diamagnetic. When such air-annealed diamagnetic substrates are used for the deposition of low-thickness films carrying low magnetic moments such as SrRuO3 and SrMnO3 thin films, their magnetic transitions are explicitly observed. The proposed annealing protocols help to improve the signal from weak magnetic samples. This allows us to analyze the film’s magnetic properties without worrying about the contribution from the substrate.

Size-dependent bistability of magnetic states in soft magnetic cap arrays

We have investigated the size dependent energy barrier regarding the transition between magnetic vortex and collinear states in dense arrays of magnetic cap structures hosting magnetic vortices. The cap structures were formed by the deposition of soft magnetic thin films on top of large arrays of densely packed polystyrene spheres. The energy barrier associated with the magnetic field assisted switching from a collinear magnetic state to a non-uniform vortex state (or vice versa) was tuned by tailoring the diameter and thickness of the soft magnetic caps. At a sufficient temperature, known as the bifurcation temperature, the thermal energy overcomes this energy barrier and magnetic bistability with a hysteresis-free switching occurs between the two magnetic states. In magnetic caps with a fixed thickness, the bifurcation temperature decreases with increasing cap diameter. On the other hand, for a fixed diameter, the bifurcation temperature increases with an increase in film thickness of the cap structure. This study demonstrates that the bifurcation temperature can be easily tailored by changing the magnetostatic energy contribution which in turn affects the energy barrier and thus the magnetic bistability.

Exploring magnetic properties and dynamic performance of magnetic-hydraulic double-floating journal bearing based on offset load

An innovative structural system of magnetic-hydraulic double-floating journal bearing is designed to improve the ability to resist offset loads. By considering the magnetic force to the water-lubricated journal bearing and the magnetic structure design, a force model of the innovative bearing is proposed. The magnetic force and water film force for the bearing are simulated by comparing the load-carry capacity of only water film force. Experimental results showed the load-carry capacity and stability test of the innovative bearing. The design of innovative bearing with the upper suction and lower magnetic repulsion based on the Halbach array can provide a larger supporting magnetic force. The axially non-uniform magnetic structure deployment can manipulate the changes of the magnetic force in the axial direction to hold the offset load. The test found that by comparing the traditional water-lubricated bearing, the bearing has a certain vibration suppression ability in the vertical direction. Under the test speed, the bearing stiffness hardly changes with the change of the speed, which also shows a slightly decreasing trend with the increase of the excitation frequency.

Actuation of microstructures with spin-current volume effect

Microactuators are essential for advances in micro-optics, ultrasonic transducers and microsensors, and there is a growing demand for miniaturization and improved power. Here we demonstrate the actuation of micromechanical structures based on spin-current volume effect using an amorphous magnetic film of TbFeCo with volume magnetostriction. A 2 mm-diameter circular polyimide diaphragm coated with thin TbFeCo/non-magnetic metal films is prepared as the micromechanical structure. When an alternating charge current flows through the TbFeCo/non-magnetic metal films on the diaphragm under an external magnetic field orthogonal to the charge current, an alternating spin-current flows in the non-magnetic metal film due to the spin-Hall effect. In the spin-current volume effect, the spin-current transports angular momentum from the non-magnetic metal to TbFeCo film, and the spin-transfer torque modulates the magnetization fluctuation of the TbFeCo film, causing the diaphragm to vibrate due to spin-lattice coupling. The power density of the TbFeCo/Pt films actuator is larger than 1.17 × 106 W m−3 at 20 mA charge current under 7.2 kOe magnetic field. This value is much higher than that of various existing film-type microactuators. This spin-current volume effect is effective as a new actuation mechanism for microactuators used in micro-optical systems, acoustic diagnostic equipment, and micro-fluidic systems etc.

Static and dynamic properties of noncollinear magnetized ferromagnetic films

Static and dynamic properties of noncollinear magnetized ferromagnetic films

Composition dependence of anomalous Nernst effect in amorphous TbFeCo thin films with perpendicular magnetic anisotropy

In this study, we systematically investigated the anomalous Nernst effect in perpendicularly magnetized amorphous TbFeCo thin films with various compositions. It was found that the magnitude of the off diagonal thermopower (ODT), which corresponds to the anomalous Nernst effect, can be uniformly explained with respect to the Tb content regardless of the concentration above or below the compensation composition. The maximum ODT of 1.3 μV/K and the thermoelectric conductivity of 1.59 A/mK at room temperature were obtained, which is more significant than other perpendicular magnetic anisotropy thin films to achieve a large Nernst voltage for roll-type thermoelectric devices. By considering the thermoelectric tensor, Mott’s equation, and the scaling law, it was shown both experimentally and theoretically that the magnitudes of the first and second terms contributing to the anomalous Nernst effect are comparable. It was also found that the ODT of TbFeCo thin films is twice or more significant than the product of the Seebeck coefficient and the Hall angle. Furthermore, amorphous metals and Mn-alloys with a large Berry curvature are located above the relation that the ODT is twice the product of the Seebeck coefficient and the Hall angle, which means that amorphous metals are expected to enhance the ANE.

Flexible and twistable free-standing PDMS-magnetic-nanoparticle-based soft magnetic films with robust magnetic properties

In this paper, we develop multifunctional, physically soft, mechanically compliant, and magnetically responsive PDMS films, with embedded Fe3O4 nanoparticles, that show robust magnetic properties over a significant range of mechanical deformation. First, we establish that the magnetic properties, namely the saturation magnetization (M s), remanent magnetization (M r), and intrinsic coercivity (H ci) of these PDMS films in highly deformed configurations, i.e. in folded, twisted (with different twist angles), and bent (flexed) configurations, show very little degradation compared to those obtained in undeformed configurations. Next, the films were subjected to repetitive cycles of zero-to-max deformation (R = 0) and the saturation magnetization of the films was shown to not exhibit any significant degree of progressive degradation as a function of cyclic deformation history. These findings confirm the excellent robustness and cyclic durability of magnetic properties shown by these magnetic and compliant PDMS films and point to their suitability for wearable electronics applications.

Oxygen adsorption on pristine MnBi and Ta-capped MnBi thin-films: Ab-initio study of structural and electronic properties, and magnetic anisotropy

We have studied the structural and electronic properties, as well as magnetic anisotropy in oxidized MnBi thin film with and without tantalum (Ta) atom as a capping layer. Spin-polarized density-functional theory calculations with the generalized gradient approximation (GGA) including U+J Hubbard correction, i.e., DFT+U+J have been employed. We found that the oxygen (O) atom binds more strongly to the MnBi surface when co-present with the Ta atom. We postulate that the strong binding prevents the O atoms from diffusing into the MnBi film layer. Thus, the Ta layer prevents surface oxidation by inducing strong binding of the O atoms to the Mn surface. Furthermore, in cases where molecular O2 is adsorbed on the Ta-capped MnBi, the O2 molecule fragments into two atomic components such that each of the O atoms relaxes to a different lattice sites on the MnBi film. Electronic structure analysis performed with this structure shows that the Ta atom on which one of the O atom is directly attached is weakly binded to the Mn. This makes it less feasible for the O atom to attach to MnBi surface. We conclude therefore, that two different mechanisms contrive to prevent MnBi surface oxidation. These are the strong binding of the O atom to the Mn which prevents the O diffusion into the MnBi film and the weak electronic bonding between the Ta and O which prevent the O atom from binding to the MnBi surface. Furthermore, we found that the presence of either Ta or O, or both, largely preserves the lattice structure of the MnBi film. With respect to the magnetic anisotropy energy (MAE), the presence of Ta capping layer restores the in-plane parallel magnetization of the pristine MnBi thin film after the latter’s oxidation. Where the direction of MAE is reversed from the in-plane to perpendicular, the perpendicular MAE is order of magnitude smaller than the in-plane MAE. This affirms the tendency of Ta capping layer to preserve either strongly or weakly, the direction of magnetization in oxidized MnBi. Our work provides the missing but highly crucial atomic level insights into an experimental study (M.Y. Sun et.al., Journal of Alloys and Compounds 672 (2016) 59-63) and has implications for the modeling of oxidation prevention via capping of magnetic thin film with external metallic atoms.

Magnetic printing characteristics of burst signals by using double magnet master media

In this study, the magnetic printing characteristics of burst signals with double magnet master (DMM) media, which consists of hard and soft magnet patterns corresponding to the burst signals, onto energy-assisted magnetic recording (EAMR) media was investigated by the micromagnetic simulation. For comparison, the magnetic printing characteristics with the conventional master media, which includes only soft magnet patterns, was also calculated. The magnetic film patterns of each master media transfer automatic-gain-control (AGC) and burst parts to the recording medium. The burst signals was amplitude AB-burst patterns, which consists of the repeated pattern region and blank area without burst patterns. Two possible master media structures of DMM media were considered, which are herein called positive- and negative- DMM media. By utilizing the positive-DMM, which spatially divides soft magnets, the AGC and the burst signals can be clearly printed, comparing with the conventional master media. While the negative-DMM is insufficient to print burst signals because the blank area without burst patterns has some non-recorded clusters. Thus, the positive-DMM are feasible for the magnetic printing of burst signals. The clear printing onto EAMR media is expected to be obtained by the optimum non-magnetic separator thickness and the optimum printing field. Therefore, the magnetic printing with positive DMM master is promising onto EAMR media.

Border effects on the ground state of an ultrathin magnetic film model

Border effects on the ground state of an ultrathin magnetic film model