Magnetic Properties Of Thin 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.

Magnetic ordering in sol-gel-based Tm3Fe5O12 thin film

In the quest to utilize rare-earth garnets (ReIG) with perpendicular magnetic anisotropy (PMA) in futuristic spintronics, the attention turned towards iron garnet thin films. Among this family, the one candidate is Tm3Fe5O12 (TmIG) that manifests PMA with excellent Gilbert damping, making this material a potential candidate in magnonics devices. Here, we report a cost-effective deposition approach of the TmIG thin films deposited on a thermally oxidized Si(100) substrate. The homogeneous TmIG (≈22 nm) thin film shows a roughness of ≈1.5 nm. The magnetic properties of thin films indicating the compensation temperature 15 K. Experimental findings present a method for the deposition of TmIG thin films, which is a potential candidate for fabricating futuristic compact devices.

Long-Term Degradation Mechanisms in Application-Implemented Radical Thin Films.

Blatter radical derivatives are very attractive due to their potential applications, ranging from batteries to quantum technologies. In this work, we focus on the latest insights regarding the fundamental mechanisms of radical thin film (long-term) degradation, by comparing two Blatter radical derivatives. We find that the interaction with different contaminants (such as atomic H, Ar, N, and O and molecular H2, N2, O2, H2O, and NH2) affects the chemical and magnetic properties of the thin films upon air exposure. Also, the radical-specific site, where the contaminant interaction takes place, plays a role. Atomic H and NH2 are detrimental to the magnetic properties of Blatter radicals, while the presence of molecular water influences more specifically the magnetic properties of the diradical thin films, and it is believed to be the major cause of the shorter diradical thin film lifetime in air.

Unraveling the temperature-dependent anomalous Hall effect in GdFeCo-Ta-TbFeCo ferrimagnetic films

The anomalous Hall effect (AHE) has been a remarkable tool for characterizing the magnetic properties of thin films with perpendicular magnetic anisotropy. In this study, we investigate the temperature-dependent AHE in sandwich structures composed of two ferrimagnetic (FIM) layers with different coercivities, using rare-earth-transition-metal (RE-TM) materials. Complex triple AHE loops are obtained near the compensation temperature of GdFeCo, and these loops are explained by considering the magnetization reversal of the individual layers, Hall sign reversal, and the spin-flop transition in the GdFeCo layer. A model is developed to provide a simplified explanation of the origin of these complex AHE loops. This study elucidates the mechanism behind the unusual temperature-dependent AHE response of the technologically important RE-TM FIM films for spintronics applications.

Improving Néel Domain Walls Dynamics and Skyrmion Stability Using He Ion Irradiation.

Ion irradiation with light ions is an appealing way to finely tune the magnetic properties of thin magnetic films and in particular the perpendicular magnetic anisotropy (PMA). In this work, the effect of He+ irradiation on the magnetization reversal and on the domain wall dynamics of Pt/Co/AlOx trilayers is illustrated. Fluences up to 1.5×1015 ions cm-2 strongly decrease the PMA, without affecting neither the spontaneous magnetization nor the strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This confirms experimentally the robustness of the DMI interaction against interfacial chemical intermixing, already predicted by theory. In parallel with the decrease of the PMA, a strong decrease of the domain wall depinning field is observed after irradiation. This allows the domain walls to reach large maximum velocities with a lower magnetic field compared to that needed for the pristine films. Decoupling PMA from DMI can, therefore, be beneficial for the design of low energy devices based on domain wall dynamics. When the samples are irradiated with larger He+ fluences, the magnetization gets close to the out-of-plane/in-plane reorientation transition, where ≈100nm size magnetic skyrmions are stabilized. It is observed that as the He+ fluence increases, the skyrmion size decreases while these magnetic textures become more stable against the application of an external magnetic field, as predicted by theoretical models developed for ultrathin films with labyrinthine domains.

Integrated experimental and theoretical studies on structural and magnetic properties of thin films of double perovskite ruthenates: Ba2DyRuO6 & Sr2DyRuO6.

Thin films of double perovskite ruthenates, viz., Ba2DyRuO6 (BDRO) and Sr2DyRuO6 (SDRO), have been successfully grown on a SrTiO3 substrate using the pulsed laser deposition technique. The BDRO samples crystallizes in cubic structure, while SDRO exhibits monoclinic structure as revealed in their X-Ray diffraction examination. Temperature-dependent magnetization measurements suggest the presence of ferromagnetism in BDRO, while paramagnetism is present for the SDRO thin film. Surprisingly, both films show canted antiferromagnetism at ∼T = 5 K as revealed in their isothermal magnetization curves. The inverse susceptibility has been fitted to the Curie-Weiss law for the SDRO sample, where the Curie temperature (TC ∼ -336.6 K) has been obtained, thus suggesting the prevalence of antiferromagnetic interactions. The existence of the canted magnetism at a lower temperature may be attributed to the Dzyaloshinskii-Moriya (D-M) interactions in the monoclinic SDRO sample due to structural distortion. However, the emergence of canted antiferromagnetism at lower temperatures (5 K) in the BDRO sample with cubic symmetry having no D-M interactions may be attributed to the various modifications at the surface of the thin films. Overall, a comparison made between the magnetic properties of both the thin films i.e., BDRO & SDRO, reveals the suppression of bulk magnetic ordering when compared to their bulk counterparts. The possible reason for the absence of any magnetic ordering in these thin films may be due to any modifications in superexchange interactions, any exchange bias, stress-strain, or uncompensated spins present in these types of thin films. UV-visible measurements for both the samples reveal a direct influence of the A-site element (Sr/Ba) on their band gaps, i.e., 3.66 eV and 2.59 eV for BDRO and SDRO samples, respectively, hence suggesting their insulating nature. We have also carried out first principles calculations with DFT using the CASTEP software to gain more insights into the experimental data. These thin films with insulating-antiferromagnetic properties may be crucial for "spintronics devices".

Anisotropic Magnetoresistance Evaluation of Electrodeposited Ni80Fe20 Thin Film on Silicon.

In this study, a simple growth of permalloy NiFe (Py) thin films on a semiconductive Si substrate using the electrochemical deposition method is presented. The electrodeposition was performed by applying a direct current of 2 mA/cm2 during different times of 120 and 150 s and thin films with different thicknesses of 56 and 70 nm were obtained, respectively. The effect of Py thickness on the magnetic properties of thin films was investigated. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), ferromagnetic resonance (FMR), anisotropic magnetoresistance (AMR), and magneto-optic Kerr effect (MOKE) analyses were performed to characterize the Py thin films. It was observed that the coercivity of the Py thin film increases by increasing the thickness of the layer. Microscopic images of the layers indicated granular growth of the Py thin films with different roughness values leading to different magnetic properties. The magnetic resonance of the Py thin films was measured to fully describe the magnetic properties of the layers. The magnetoresistance ratios of deposited Py thin films at times of 120 and 150 s were obtained as 0.226% and 0.235%, respectively. Additionally, the damping constant for the deposited sample for 120 s was estimated as 1.36 × 10-2, which is comparable to expensive sputtered layers' characteristics.

A short-circuited coplanar waveguide for low-temperature single-port ferromagnetic resonance spectroscopy setup to probe the magnetic properties of ferromagnetic thin films

A coplanar waveguide shorted in one end is proposed, designed, and implemented successfully to measure the properties of magnetic thin films as a part of the vector network analyzer ferromagnetic resonance (FMR) spectroscopy setup. Its simple structure, potential applications, and easy installation inside the cryostat chamber made it advantageous especially for low-temperature measurements. It provides a wide band of frequencies in the gigahertz range essential for FMR measurements. Our spectroscopy setup with a short-circuited coplanar waveguide has been used to extract the Gilbert damping coefficient and effective magnetization values for standard ferromagnetic thin films, such as Permalloy (Py) and Cobalt (Co). The thickness and temperature-dependent studies of those magnetic parameters have also been done here for the afore-mentioned magnetic samples.

Interfacial mixing effect in a promising skyrmionic material: Ferrimagnetic Mn4N

Interfacial mixing of elements is a well-known phenomenon found in thin film deposition. For thin-film magnetic heterostructures, interfacial compositional inhomogeneities can have drastic effects on the resulting functionalities. As such, care must be taken to characterize the compositional and magnetic properties of thin films intended for device use. Recently, ferrimagnetic Mn4N thin films have drawn considerable interest due to exhibiting perpendicular magnetic anisotropy, high domain-wall mobility, and good thermal stability. In this study, we employed x-ray photoelectron spectroscopy (XPS) and polarized neutron reflectometry (PNR) measurements to investigate the interfaces of an epitaxially grown MgO/Mn4N/Pt trilayer deposited at 450 °C. XPS revealed the thickness of elemental mixing regions of near 5 nm at both interfaces. Using PNR, we found that these interfaces exhibit essentially zero net magnetization at room temperature. Despite the high-temperature deposition at 450 °C, the thickness of mixing regions is comparable to those observed in magnetic films deposited at room temperature. Micromagnetic simulations show that this interfacial mixing should not deter the robust formation of small skyrmions, consistent with a recent experiment. The results obtained are encouraging in terms of the potential of integrating thermally stable Mn4N into future spintronic devices.

Surface roughness effects on magnetic properties of thin films: A computational Monte Carlo study

By means of Monte Carlo simulation, a computational approach is proposed to investigate the surface roughness effects on the critical and hysteresis behaviors of Heisenberg ferromagnetic thin films. Here, the atomic sites of the film’s surface are changed systematically from their regular positions using a disorder parameter, thereby allowing us to smoothly interpolate between smooth and rough surfaces. Threshold values of the structural disorder level at which the system critical temperature increases are identified. Furthermore, the surface roughness increases is observed to have a profound impact on the system’s magnetic hysteresis loops. In particular, a significant increase in the loop’s area is observed as the roughness increases, thereby increasing the coercivity of the thin magnetic film.

Magnetic domain wall pinning in cobalt ferrite microstructures

A detailed correlative structural, magnetic and chemical analysis of (non-stoichiometric) cobalt ferrite micrometric crystals was performed by x-ray magnetic circular dichroism combined with photoemission microscopy, low-energy electron microscopy and atomic force microscopy. The magnetization vector inside the islands was resolved at the nanoscale, as obtained from magnetic images taken at different x-ray incidence angles. The location of the magnetic domain walls was correlated with the presence of different types of defects as revealed by the different microscopies. This, together with the results of micromagnetic simulations, suggests that the main source of pinning in these microcrystals are linear structural defects induced in the spinel structure by the substrate steps underneath the islands. Our result is of relevance for understanding the different magnetic properties of thin films and nanostructures as compared with the corresponding bulk materials.

Self-assembled growth and magnetic properties of Fe and FeTiO3 core–Sr(Ti,Fe)O3 shell nanocomposites

In this study, a promising method for the modulation of the microstructure, composition, and magnetic properties of thin films fabricated by co-sputtering metallic Fe and oxide SrTiO3 targets is proposed. The proposed method can potentially be applied in multifunctional electronics. The flat surface morphology was observed in the thin film sputtered under a low power for the Fe target, whereas micro-height rods were fabricated on an uneven layer at a higher power. Strong magnetic anisotropy was not observed in the co-sputtered thin films because of the randomly oriented growth of the magnetic rods. Detailed microstructural and compositional studies using high-resolution transmission electron microscopy and scanning transmission electron microscopy revealed that self-assembled nanocomposites with three components were grown with a core–shell structure, in which Fe and FeTiO3 phases grew in the Sr(Ti,Fe)O3 matrix. This report provides an insight into designing multifunctional metal–metal oxide nanocomposites with single-step co-sputtering, which is capable of adjusting the composition and geometry of the nanocomposites.

Volume effects on microstructures and magnetic properties of MnGa thin films during order-disorder transformation

In this study, L10 MnGa thin films were grown on an amorphous glass substrate, and the relationship between the volume effect and the magnetic properties of thin films as a function of the film thickness was investigated. An amorphous thin film and weak magnetic properties were observed at the thickness of 10 nm. With the increase in thickness, the magnetization (M10 kOe) and coercivity (Hc⊥) also increased. The maximum M10 kOe and Hc⊥ values were 106.3 ± 5.7 emu/cm3 and 8.54 kOe in a 200 nm-thick sample, respectively. X-ray diffraction indicated that the order-disorder transformation occurred when the thickness was greater than 25 nm. Plan-view transition electron microscopy (TEM) images indicated the emergence of larger grains and blurred grain boundaries when the thickness was increased beyond 25 nm, while cross-sectional TEM images suggested that the appearance of nuclei promote the growth of columnar MnGa grain structures. Energy dispersion spectroscopy analysis indicated that the composition of MnGa was Mn-rich (or Ga-poor) in the nuclei at the initial growth state and then gradually changed to Mn50Ga50 as the thickness increased. In addition, the effects of the base pressure of the chamber on the phase and magnetic properties of the MnGa films were also investigated.

Composition and magnetic properties of thin films grown by interdiffusion of Mn and Sn-Rich, Ge lattice matched SixGe1-x-ySny layers

We report on the structure and magnetic properties of Mn based ferromagnetic layers on the semiconductor SixGe1-x-ySny with Sn content up to y = 0.15 in comparison with layers on Ge and Si0.75Ge0.25. The ferromagnetic layers grow by interdiffusion between an evaporated Mn layer and molecular-beam-epitaxy grown semiconductor layers. This approach enables the preparation of Mn based layers, e.g., as a ferromagnetic contact material for SixGe1-x-ySny using a self-aligned interdiffusion process, opening up the opportunity for large-scale manufacturing. The samples show a clear phase separation into Si-rich and Ge-rich Mn compounds. All samples are ferromagnetic and exhibit a decrease in saturation magnetization and an increase in coercive field with increasing Si content x. The Curie temperature shows no decisive trend with increasing Si content with values around room temperature. Based on the composition, structure and magnetic properties, we propose a two-layer model to correlate the structure and composition with the observed magnetic properties. We show that the changes in magnetic behavior can be explained solely by considering the Si content of the SixGe1-x-ySny substrates with the Sn being largely passive.

Inhomogeneous magnetic properties characterized by simultaneous electrical and optical detection of spin-torque ferromagnetic resonance

Magnetic properties of the Pt/Py microstrip were investigated using the simultaneous electrical and optical detection of spin-torque ferromagnetic resonance. From the measured optical signal using the heterodyne-magneto-optical Kerr effect (MOKE), we found that the inhomogeneous broadening and Gilbert damping constant were modified along the transverse direction of the microstrip. In addition, a difference in the precession phase was also observed owing to the non-uniform out-of-plane microwave field. Our study shows that the ferromagnetic resonance measurement based on the heterodyne-MOKE technique is a powerful tool for characterizing the static and dynamic magnetic properties of magnetic thin films with sub-micrometer spatial resolution.

Numerical study of structural and magnetic properties of thin films obliquely deposited on rippled substrates

Structural modulation in thin films plays a substantial role in the formation of their magnetic properties. By producing topographic patterns in thin films, it is possible to engineer their magnetic response. Here, we report on the numerical study of the relationship between structural and static magnetic properties of thin films obliquely deposited on substrates with the sinusoidal surface. 3D Monte Carlo film growth simulations show that, under certain deposition conditions, an inhomogeneous columnar morphology can form in the films caused by the shadowing effect and the rippled substrate. Calculations of the demagnetizing tensors for these films demonstrate that their columnar structure is the source of the shape-induced uniaxial magnetic anisotropy that varies nonmonotonically with the deposition angle. Micromagnetic simulations of the generated films confirm the uniaxial character of the shape-induced anisotropy, and also show that magnetization reversal occurs via an incoherent rotation of magnetic moments.

Magnetic and structural characteristics of ambient pressure fcc phase Ho and Tb thin films

We report the results of an investigation into the structural and magnetic properties of thin films of Ho and Tb sputtered on Ta-buffered Si substrates. As is often reported in thin films and nanoparticles of the rare earth (RE) metals, we observe both hcp and fcc phases where the relative fraction of each depends on the deposition conditions. The presence of a fcc RE phase at ambient conditions is generally claimed to be strain stabilised as in the bulk the fcc phase is only thermodynamically stable at elevated pressures. We find the lattice constants of the fcc phases in our films to coincide with values for the Ho- and Tb- hydrides, and analysis of the magnetic measurements shows that the Ho fcc phase is paramagnetic at ambient temperatures and antiferromagnetic at low temperatures, also a feature of the RE-hydrides. By considering both the structural and magnetic measurements on Ho and Tb films together, we demonstrate that the observed fcc phase is the antiferromagnetic rare earth hydride, which readily forms at the RE/Ta interface in the presence of the residual and outgassed hydrogen in vacuum chambers.

Structural and magnetic properties of CoIrMnAl equiatomic quaternary Heusler alloy epitaxial films designed using first-principles calculations

• CoIrMnAl was computationally designed as one of the advanced materials for spintronics. • We obtained B2 ordered CoIrMnAl thin films with the lattice constant similar to that predicted in fully ordered alloy. • Magnetization at 10 K and Curie temperature measured were about 70% of the predicted values in fully ordered alloys. • Experimental data were well explained with ferrimagnetism due to Co-Mn swap disorders predicted from ab-initio calculation. MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy electrodes have attracted considerable attention for spintronics applications. However, there remain a couple of issues related to materials that should be resolved before practical use. Recently, quarterly equiatomic Heusler alloys have attracted attention as advanced Heusler alloys. CoIrMnZ (Z = Al, Si, Ga, and Ge) half-metallic Heusler alloys were designed and predicted to have moderate Curie temperatures and to be lattice-matched with the MgO barrier, which is advantageous compared to traditional Co 2 Heusler alloys T. T [T. Roy et al., J. Magn. Magn. Mater. 498 (2020) 166092]. Here, we experimentally investigated the structure and magnetic properties of thin films composed of one of these alloys, CoIrMnAl, fabricated by sputtering deposition. We successfully obtained films with the B 2 chemical ordering, even without a post-annealing process. The lattice constants for the films annealed at 500–600 ∘ C were approximately equal to the predicted values. The magnetization at 10 K was close to 500 kA/m, and the Curie temperature was approximately 400 K, which were approximately 70% of the values predicted for the fully ordered structure. The magnetic properties observed in the B 2-ordered films were well explained by ferrimagnetism that appeared in the B 2-ordered CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap disorder of Co-Mn, which was predicted from the first-principles calculations.

The Influence of Pressure on the Formation of FM/AF Configurations in LSMO Films: A Monte Carlo Approach

In this work, Monte Carlo simulations of magnetic properties of thin films, including the influence of an external pressure, are presented. These simulations were developed using a Hamiltonian composed by terms that represent the exchange interaction, dipolar interaction, Zeeman effect, monocrystalline anisotropy, and pressure influence. The term that represents the pressure influence on the magnetic properties was included, since for many applications, magnetic materials are a part of a multiferroic material together with a piezoelectric or a ferroelectric compound. Initially, the model was developed using generic parameters, in order to probe its suitable performance; after that, parameters were adjusted for simulating thin films of La0.67Sr0.33MnO3, a manganite with several technological applications because its Curie temperature is greater than room temperature. Including the pressure influence, it was observed the formation of several kind of FM/AF configurations as strip, labyrinth, and chess board forms. Furthermore, it was observed that, as the pressure increased, the critical temperature tended to decrease, and this result was in agreement with experimental reports.

Measurement of the magnetic properties of thin films based on the spin Hall effect of light.

Using the spin Hall effect of light, this work proposes a measurement technique of the magnetic properties of thin films. The beam shift of the spin Hall effect of light is used to replace the magneto-optical Kerr rotation angle as a parameter to characterize the magnetism of thin films. The technique can easily achieve an accuracy of 10-6 rad of the magneto-optical Kerr rotation angle which can, in theory, be further improved to 10-8 rad. We also proposed two methods to solve the problem of the exceeding linear response region of the measurement under high magnetic field intensity, making it more conducive to practical application. This technique has great potential for application in the magnetic measurement of ultra-thin films with particular emphasis on thicknesses within several atomic layers.