Film Plane Research Articles

IEEE Magnetics Society Distinguished Lecturers for 2022

Electric manipulation of magnetization is essential for the integration of magnetic functionalities in integrated circuits. Spin-orbit torque (SOT), originating from the coupling of electron spin and orbital motion through spin-orbital interaction, can effectively manipulate magnetization. Symmetry breaking plays an important role in spintronics based on SOT. SOT requires inversion asymmetry in order to have a net effect on magnetic materials, which is commonly realized by spatial asymmetry: a thin magnetic layer sandwiched between two dissimilar layers. This kind of structure restricts the SOT by mirror and rotational symmetries to have a particular form: an “antidamping-like” component oriented in the film plane even upon reversal of the magnetization direction. Consequently, magnetization perpendicular to the film plane cannot be deterministically switched with pure electric current. To achieve all-electric switching of perpendicular magnetization, it is necessary to break the mirror and rotational symmetries of the sandwiched structure.

Study on the formation and mechanism of aluminum bulge defect in semiconductor integrated circuit manufacturing

With the development of semiconductor integrated circuit manufacturing technology, the defects that lead to yield failure are also occurring constantly. In our work, the aluminum bulge defects in the metallization process are briefly analyzed, it will lead to macroscopic chromatic aberration and yield failure. It was confirmed by analyzing the crystal structure of titanium nitride (TiN), which the (111) crystal plane of TiN film can greatly improve the surface roughness of film. On the other hand, by changing the etching conditions of tungsten film, the etching selectivity ratio of tungsten film and TiN film is increased, so as to reduce the defects. Thus, the main factors affecting the bulge defects in the metallization process include the microstructure of TiN film and the etching process of tungsten film.

DC and AC tunneling magnetoelectric responses of cobalt lateral nanogranular films

We demonstrate a new structural optimization of cobalt–(barium fluoride) lateral nanogranular films, achieving independently variable direct current (DC) and alternating current (AC) tunneling effects, in the film plane and out of the plane, respectively. Lateral nanogranular films were successfully fabricated via programmable tandem sputtering. Flat-shaped magnetic Co nanogranules were periodically inserted between dielectric barium fluoride layers of different thicknesses. All the lateral nanogranular films were insulating, with electrical resistivities ρ exceeding 1013 μΩ·cm, even with a Co content as high as 30 at.%. A lateral tunneling magnetoresistance (TMR) effect and vertical tunneling magnetodielectric (TMD) effect were found in the same lateral nanogranular film with 30 at.% Co. For a nanogranular film with lateral Co nanoparticles, the sensitivity of both the TMR and TMD ratio were improved at small magnetic fields compared with conventional films with spherical Co nanoparticles, reflecting its small saturation magnetic field. This layer-ordered metal–insulator nanogranular structure has potential applications in AC/DC hybrid elements as a high-sensitivity magnetic sensor.

Orientation Dependent Mechanical Responses and Plastic Deformation Mechanisms of ZnSe Nano Films under Nanoindentation.

Although ZnSe has been widely studied due to its attractive electronic and optoelectronic properties, limited data on its plastic deformations are available. Through molecular dynamics simulations, we have investigated the indentations on the (001), (110), and (111) planes of ZnSe nano films. Our results indicate that the elastic modulus, incipient plasticity, elastic recovery ratio, and the structural evolutions during the indenting process of ZnSe nano films show obvious anisotropy. To analyze the correlation of structural evolution and mechanical responses, the atomic displacement vectors, atomic arrangements, and the dislocations of the indented samples are analyzed. Our simulations revealed that the plastic deformations of the indented ZnSe nano films are dominated by the nucleation and propagation of 1/2<110> type dislocations, and the symmetrically distributed prismatic loops emitted during the indenting process are closely related with the mechanical properties. By studying the evolutions of microstructures, the formation process of the dislocations, as well as the formation mechanisms of the emitted prismatic loops under the indented crystalline planes are discussed. The results presented in this work not only provide an answer for the questions about indentation responses of ZnSe nano films, but also offer insight into its plastic deformation mechanisms.

Fast uptake of organic pollutants from dilute aqueous solutions by nanoporous-crystalline PPO films with c-perpendicular orientation

The extraordinary ability of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) dense films, exhibiting a nanoporous-crystalline (NC) phase, to absorb traces of organic pollutants dissolved in water is shown. Equilibrium uptakes and sorption kinetics of perchloroethylene (PCE) are much higher and faster than for the corresponding amorphous films. For sorption kinetics, particularly relevant is a control of the planar orientation of the NC phase. For instance, for PCE sorption from 50 ppm aqueous solutions, a NC α form film with orientation of the crystalline polymer chains being preferentially perpendicular to the film plane (c⊥ orientation) exhibit a diffusivity nearly 14 times higher than for a NC film with crystalline polymer chains being preferentially parallel to the film plane (c// orientation) and nearly 88 times higher than for the starting amorphous PPO film. This phenomenon is rationalized in terms of crystalline channels being preferentially perpendicular to the film plane. Moreover, equilibrium uptakes for NC PPO films are much higher than for NC sPS films. For instance, for sorption experiments from PCE 50 ppm aqueous solutions, equilibrium uptakes for NC PPO and sPS films are nearly 15 wt% and 2 wt%, respectively. This phenomenon is rationalized by the high-free volume of both NC and amorphous phases of PPO.

Electric field control of magnetism in FePt/PMN-PT heterostructures

Laminar heterostructures composed by materials with different ferroic properties have been proposed for the control of magnetism with an applied voltage. We present here a study of the structural and magnetic properties of chemically disordered FePt ferromagnetic films of different thicknesses that have been sputter-deposited on ferroelectric PMN-PT (011) single crystals.By means of static and dynamic magnetic measurements we have found that it is possible to switch the magnetization easy axis by 90° if an electric field is applied in a direction perpendicular to the film plane. Using ferromagnetic resonance techniques we have estimated the strain induced magnetoelectric coupling of the FePt/PMN-PT heterostructure, obtaining ME=477(15) Oe m/MV for FePt thicknesses greater than 26 nm, which corresponds to an average magnetoelastic constant B=−13.2(1.1) MJ/m3. The associated saturation magnetostriction was estimated in λs∼90 ppm. Films thinner than 26 nm present corresponding values that are smaller by approximately 20%. A possible explanation for this difference is the well known transition from planar to stripe-like magnetic domains that occurs in FePt around this film thickness. However, this thickness dependence of ME is relatively smaller than that found in other ferromagnets such as Fe or FeGa, which makes FePt a potential candidate for thin film applications in magnetoelectronic devices.

Mechanisms determining different planar orientations in PPO films crystallized by guest sorption

Co-crystallization of amorphous poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) films, as induced by sorption at different temperatures of many liquid guest molecules, is explored. Both for co-crystalline (CC) and corresponding nanoporous-crystalline (NC) films, kinds of and degree of planar orientation, which are relevant for their properties and applications, can be controlled by the guest sorption procedure. In particular, crystalline polymer chain orientation preferentially perpendicular to the film plane is favored by bulky guest molecules and by low guest sorption temperatures, i.e. by slow guest uptakes. Guest sorption kinetics and Scanning Electron Microscopy (SEM) support a simple mechanism that rationalizes the kinds of planar orientation of crystalline PPO chains. Slow guest uptakes imply polymer co-crystallization in spatial confinement, producing lamellae that are oriented flat-on to the film surface and hence polymer chain axes preferentially perpendicular to the film plane (c⊥ orientation). Fast guest uptakes imply polymer co-crystallization leading to fibrils that are parallel to the film surface and hence to polymer chain axes being preferentially parallel to the film plane (c// orientation).

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Anisotropic terahertz transmission induced by the external magnetic field in La0.67Ca0.33MnO3 film.

A systemic investigation of the terahertz (THz) transmission of La0.67Ca0.33MnO3 film on the (001)-oriented NdGaO3 substrate under external magnetic field and low temperature have been performed. The significant THz absorption difference between the out-of-plane and the in-plane magnetic field direction is observed, which is consistent with the electrical transport measurement using the standard four-probe technique. Furthermore, we find that the complex THz conductivities can be reproduced in terms of the Drude Smith equation as the magnetic field is perpendicular to the film plane, whereas it deviates from this model when the in-plane magnetic field is applied. We suggest that such anisotropies in THz transport dynamics have close correspondences with the phase separation and anisotropic magnetoresistance effects in the perovskite-structured manganites. Our work demonstrates that the THz time-domain spectroscopy (TDS) can be an effective non-contact method for studying the magneto-transport properties of the perovskite-structured manganites.

Coherent GHz lattice and magnetization excitations in thin epitaxial Ag/Fe/Cr/Fe films

We excited an epitaxial magnetic Ag/Fe/Cr/Fe multilayer nonthermally and nonoptically with very short (1 ps) electromagnetic pulses. We detected the synchronous phononic-magnetic response by time-resolved magneto-optical Kerr effect measurements. The Ag/Fe/Cr/Fe multilayer was patterned into a coplanar waveguide transmission line, and the electromagnetic pulses were generated by pulsed-laser illumination of an integrated GaAs photoconductive switch (PCS). The detected magnetic excitations comprise up to four narrow-band high-order modes with the highest frequency reaching 30 GHz. The mode frequencies are independent of both temperature in the range from 16 to 300 K and the applied external magnetic field up to 120 mT. Our analysis shows that the origin of the rigidity of these high-frequency modes is the strong coupling of the magnetic subsystem with the lattice of the Ag/Fe/Cr/Fe multilayer. The exciting electromagnetic pulse generated by the PCS induces, via magnetoelastic coupling, long-lived (ns) standing GHz acoustic waves normal to the Ag/Fe/Cr/Fe film plane. These lattice oscillations in turn couple back and drive the magnetization oscillations via the magnetoelastic coupling. The temperature and field dependence of the damping of the oscillations can be described by inelastic phonon-phonon and phonon-magnon scattering. Our study opens up a possibility of using coherent lattice and magnetization dynamics in ferromagnetic films for spintronic devices at GHz clock rates.

Spin\u2013orbit torque driven magnetization switching in W/CoFeB/MgO-based type-Y three terminal magnetic tunnel junctions

We have studied current induced magnetization switching in W/CoFeB/MgO based three terminal magnetic tunnel junctions. The switching driven by spin—orbit torque (SOT) is evaluated in the so-called type-Y structure, in which the magnetic easy-axis of the CoFeB layer lies in the film plane and is orthogonal to the current flow. The effective spin Hall angle estimated from the bias field dependence of critical current (Ic) is ~ 0.07. The field and current dependence of the switching probability are studied. The field and DC current induced switching can be described using a model based on thermally assisted magnetization switching. In contrast, the 50 ns long pulse current dependence of the switching probability shows significant deviation from the model, even if contribution from the field-like torque is included. The deviation is particularly evident when the threshold switching current is larger. These results show that conventional thermally assisted magnetization switching model cannot be used to describe SOT induced switching using short current pulses.

Magnetoelasticity of Fe1−xGax thin films on amorphous substrates

In this work, we study the magnetoelastic behavior of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}$ ($0.11&lt;x&lt;0.19$) thin films, grown on glass and oxidized Si(100) amorphous substrates, that present an isotropic crystalline texture in the film plane. The magnetoelastic coupling coefficients are obtained through the cantilever deflection technique. We find that the magnetoelastic response is larger for samples grown on glass with respect to those grown on Si(100), and such a response increases for larger Ga concentrations for both substrates used. Furthermore, the increasing substrate temperature during growth does not appear to have a significant effect on magnetoelastic behavior of samples grown on Si(100). From a model that takes into account the elastic grain interaction for isotropic systems, we are able to describe the experimentally observed behavior. We find that the magnetoelastic response of the samples grown on glass are well described by the Voigt model, while the samples on Si(100) present an intermediate response between the Voigt and Reuss models.

Magnetic Anisotropy Induced by Orbital Occupation States in La0.67Sr0.33MnO3 FilmsSupported by the National Key Research Program of China (Grant Nos. 2017YFA0206200, 2016YFA0300701, and 2018YFA0208402), the National Natural Science Foundation of China (Grant Nos. 11934017, 11874413, 11574376, and 51972333), the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No. XDB33030200), and the Youth Innovation Promotion Association of the Chinese

Interface engineering is an effective and feasible method to regulate the magnetic anisotropy of films by altering interfacial states between films. Using the technique of pulsed laser deposition, we prepared La0.67Sr0.33MnO3 (LSMO) and La0.67Sr0.33MnO3/SrCoO2.5 (LSMO/SCO) films on (110)-oriented La0.3Sr0.7Al0.65Ta0.35O3 substrates. By covering the SCO film above the LSMO film, we transformed the easy magnetization axis of LSMO from the [001] axis to the [] axis in the film plane. Based on statistical analyses, we find that the corresponding Mn–Mn ionic distances are different in the two types of LSMO films, causing different distortions of Mn–O octahedron in LSMO. In addition, it also induces diverse electronic occupation states in Mn3+ ions. The e g electron of Mn3+ occupies 3z 2 – r 2 and x 2 – y 2 orbitals in the LSMO and LSMO/SCO, respectively. We conclude that the electronic spin reorientation leads to the transformation of the easy magnetization axis in the LSMO films.

Tailoring interface alloying and magnetic properties in (111) Permalloy/Pt multilayers

We demonstrate preparation and characterization of permalloy Ni80Fe20 at.% (Py) multilayers in which the Py layers were deposited by two different sputter deposition methods. Namely, dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS), that represent low and moderate ionized flux fraction of the film forming material, respectively. We deposited ultrathin bilayers, i.e. 15 Å thick Py and 5 Å thick Pt, with 20 repetitions. Various effects such as substrate roughness, working gas pressure and sputter power are considered. The microstructure, texture and strain were characterized by X-ray diffraction, individual thicknesses and alloying were analysed by X-ray reflectivity, and uniaxial in-plane anisotropy probed by the magneto-optical Kerr effect. It is shown that HiPIMS deposition produces multilayers with reduced surface roughness regardless of the substrate surface roughness. Both dcMS and HiPIMS deposition present multilayers with strong (111) texture normal to the substrate. Using HiPIMS for deposition of the Py layer minimizes the alloying between individual layers compared to dcMS deposition performed at same average sputter power. However, this improvement in interface sharpness leads to a higher magnetic coercivity and a poor hard axis in the film plane. On the other hand, multilayers with alloying present a linear hard axis. Furthermore, we studied Py/Cu and Py/CuPt multilayers, prepared under identical conditions using HiPIMS. The results indicate that in the Py/Pt case, deterioration of the in-plane uniaxial anisotropy, is caused by inverse magnetostriction originating from the large lattice mismatch between Py and Pt. The Py/Pt multilayers that exhibit alloying have a less strained interface and have a well defined uniaxial anisotropy.

Electrostatic model of dielectric elastomer generator based on finite element

When dielectric elastomer materials are used for power generation, bias voltage is applied at both ends of dielectric elastomer film, and there are equal amounts of heterogeneous charges on both sides of the film, so Maxwell electrostatic force is always coupled in the process of power generation. In order to investigate the distribution of Maxwell stress in dielectric elastomer material under electric field, the electrostatic model of dielectric elastomer generator is established in COMSOL finite element simulation software environment in this paper. The distribution of electrostatic force is studied from two aspects of theoretical derivation and simulation, and the magnitude and direction of electrostatic force are determined. The simulation results show that the Maxwell electrostatic force can be equivalent to the tensile force along the film plane and the extrusion force perpendicular to the plane, and they are the same.

High diffusivity dense films of a nanoporous-crystalline polymer

Nanoporous-crystalline (NC) films of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) exhibit much higher guest uptakes with respect to amorphous PPO films as well as with respect to films based on different polymers. Particularly high guest diffusivities are observed for PPO films with orientation of the chain axes of their NC phases being preferentially perpendicular to the film plane (c⊥ orientation). Remarkably high diffusivities of c⊥ oriented NC PPO films are also observed for high film thickness (at least up to 50 μm). This phenomenon is due to the high free-volume of the amorphous PPO phase combined with crystalline channels being preferentially perpendicular to the film plane. Guest uptakes for NC PPO films, when expressed as mass/volume, are also much higher than for NC PPO powders and high-surface-area NC PPO aerogels, as well as much higher than for benchmark adsorbent polymers (Tenax). High guest uptakes and diffusivities of NC PPO films with c⊥ orientation are relevant for their possible applications as dense membranes for organic pollutant control, molecular separations and molecular sensors.

Ориентационные характеристики возбуждения прецессии намагниченности на интерференционной решетке, создаваемой фемтосекундным лазером.

The subject of investigation in this work is the excitation of magnetization precession in magnetic film on the surface of which is formed the temperature relief which is formed by interference picture formatted by preliminary divided ray from femtosecond laser. It is mentioned the discovered in experiment the dependence of excitation efficiency from the orientation of magnetic field applied in the plane of film. The main aim of this work is the theoretical interpretation of observed orientation dependence. The realized in experiment scheme “pump-probe” is described. The whole geometry of task is proposed. This geometry includes in oneself the magnetic film with formed in its surface interference picture and applied in the plane of film the constant field. It is shown that by the thermal expansion in the film the elastic waves two types are excited; the surface Rayleigh waves and leaky longitudinal waves. The projections of wave-vectors of propagating waves to plane of film are normal to the strips of interference picture. The orientation of field may change from to longitudinal to transverse from the same strips. The components of deformation tensor of Rayleigh and leaky waves are determined. The precession of magnetization in the coordinate system connected with field is investigated. By using the apparatus of crossing matrixes it is found the components of deformation tensor are determined. In the frame of linear approach in this system the task about excitation of magnetization precession by elastic deformations by Rayleigh and leaky waves is solved. The dynamical component of magnetization precession which ensures the light polarization rotation which passes along the normal to the plane of film is found. It is shown that the angle of rotation is straight proportional to the tensor deformation components with the summarization with the resonance character of precession magnetization dependence from the value of magnetic field. The dependence of polarization rotation from orientation of field which is applied in the plane of film is found. It is shown that by the orientation of field along and across the interference stripes the rotation of polarization plane is absent. Between these extreme orientations the dependence has appearance as two maxima divided by deep minimum. The received results are compared with data of experiment. It is found the quality and in some cases quantity correlation. The recommendations for further development of work are proposed.

Magnetocrystalline anisotropy and volume ratio of FePt grains with c-axes parallel to the film plane in FePt granular film with various grain boundary materials

In this study, we analyzed the structure for FePt grains whose c-axes are parallel to the film plane (in-plane grains) and the effect of the grains on magnetic properties. According to the analysis for granular films with a constant GBM volume of 30 vol% deposited at a high substrate temperature, the structure such as the lattice constant c, a and degree of order for in-plane grains was estimated to be the same as that of FePt grains whose c-axes are normal to the film plane (normal grains). In addition, it was found that perpendicular magnetic anisotropy was dependent on both the ratio of in-plane grains to the normal grains (R parallel) and the degree of order. Considering R parallel and the volume of GBM, magnetocrystalline anisotropy (K u grain) is estimated to be 3.43 × 107 (erg cm−3) for perfect ordering FePt grains.

ZnO Nanorods Grown on Heterogenous Ag Seed Layers for Single-Cell Fluorescence Bioassays

Here we demonstrate the controllability of the morphology of hydrothermal ZnO nanorods (ZnO-NRs) grown on heterogenous Ag seed layers. By varying the crystal orientation of silver thin films (Ag), a high density of ZnO-NRs could be obtained. We find that the density of ZnO-NRs strongly relates to the peak intensity ratio between (111) and (200) planes of Ag thin films due to a heteroepitaxy between (0002) ZnO and (111) Ag rather than that of grain boundary nucleation and/or surface nucleation. In addition, the optimized heterostructure of ZnO nanorod/Ag arrays is investigated via a critical concentration for nucleation and used as a fluorescence enhancement substrate (FES). The experimental results have shown that the FES presents an ability to detect a biological sample (PC-3 cell) with a high sensitivity and low detection limit of 1 cell/μL. Our results highlight that understanding an important key to control and design the morphology of heterogeneous hydrothermal ZnO-NR growth is essential to open up the opportunities for fundamental studies and applications in high-performance integrated nanodevices.

Measurement-based range evaluation for quality assurance of CBCT-based dose calculations in adaptive proton therapy.

The implementation of volumetric in-room imaging for online adaptive radiotherapy makes extensive testing of this image data for treatment planning necessary. Especially for proton beams the higher sensitivity to stopping power properties of the tissue results in more stringent requirements. Current approaches mainly focus on recalculation of the plans on the new image data, lacking experimental verification, and ignoring the impact on the plan re-optimization process. The aim of this study was to use gel and film dosimetry coupled with a three-dimensional (3D) printed head phantom (based on the planning CT of the patient) for 3D range verification of intensity-corrected cone beam computed tomography (CBCT) image data for adaptive proton therapy. Single field uniform dose pencil beam scanning proton plans were optimized for three different patients on the patients' planning CT (planCT) and the patients' intensity-corrected CBCT (scCBCT) for the same target volume using the same optimization constraints. The CBCTs were corrected on projection level using the planCT as a prior. The dose optimized on planCT and recalculated on scCBCT was compared in terms of proton range differences (80% distal fall-off, recalculation). Moreover, the dose distribution resulting from recalculation of the scCBCT-optimized plan on the planCT and the original planCT dose distribution were compared (simulation). Finally, the two plans of each patient were irradiated on the corresponding patient-specific 3D printed head phantom using gel dosimetry inserts for one patient and film dosimetry for all three patients. Range differences were extracted from the measured dose distributions. The measured and the simulated range differences were corrected for range differences originating from the initial plans and evaluated. The simulation approach showed high agreement with the standard recalculation approach. The median values of the range differences of these two methods agreed within 0.1mm and the interquartile ranges (IQRs) within 0.3mm for all three patients. The range differences of the film measurement were accurately matching with the simulation approach in the film plane. The median values of these range differences deviated less than 0.1mm and the IQRs less than 0.4mm. For the full 3D evaluation of the gel range differences, the median value and IQR matched those of the simulation approach within 0.7 and 0.5mm, respectively. scCBCT- and planCT-based dose distributions were found to have a range agreement better than 3mm (median and IQR) for all considered scenarios (recalculation, simulation, and measurement). The results of this initial study indicate that an online adaptive proton workflow based on scatter-corrected CBCT image data for head irradiations is feasible. The novel presented measurement- and simulation-based method was shown to be equivalent to the standard literature recalculation approach. Additionally, it has the capability to catch effects of image differences on the treatment plan optimization. This makes the measurement-based approach particularly interesting for quality assurance of CBCT-based online adaptive proton therapy. The observed uncertainties could be kept within those of the registration and positioning. The proposed validation could also be applied for other alternative in-room images, e.g. for MR-based pseudoCTs.