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In this study, we investigate the effect of temperature on the performance of a read sensor by utilizing an atomistic model coupled with a spin transport model. Specifically, we study the temperature dependence of spin transport behavior and MR outputs in a Co 2 FeAl 0.5 Si 0.5 (CFAS)(5nm)/Cu(5nm)/CFAS(5nm) trilayer with diffusive interfaces. Initially, the two-channel model of spin-dependent resistivity is used to calculate the temperature dependence of spin transport parameters which serves as essential input for the spin accumulation model. Our findings demonstrate that as the temperature increases, the spin transport parameters and magnetic properties decrease due to the influence of thermal fluctuation. At a critical temperature, where the ferromagnet transitions to a paramagnetic state, we observe zero spin polarization. Furthermore, at elevated temperatures, the spin accumulation deviates from the equilibrium value, leading to a reduction in the magnitude of spin current and spin transport parameters due to thermal effects. As a consequence, the MR ratio decreases from 65% to 20% with increasing temperature from 0 to 400 K. Our results are consistent with previous experimental measurements. This study allows to deeply understand the physical mechanism in the reader stack which can significantly benefit reader design., (© 2024. The Author(s).)

We demonstrate magnetic droplet soliton pairs in all-perpendicular spin-torque nano-oscillators (STNOs), where one droplet resides in the STNO free layer (FL) and the other in the reference layer (RL). Typically, theoretical, numerical, and experimental droplet studies have focused on the FL, with any additional dynamics in the RL entirely ignored. Here we show that there is not only significant magnetodynamics in the RL, but the RL itself can host a droplet driven by, and coexisting with, the FL droplet. Both single droplets and pairs are observed experimentally as stepwise changes and sharp peaks in the dc and differential resistance, respectively. While the single FL droplet is highly stable, the coexistence state exhibits high-power broadband microwave noise. Furthermore, micromagnetic simulations reveal that the pair dynamics display periodic, quasi-periodic, and chaotic signatures controlled by applied field and current. The strongly interacting and closely spaced droplet pair offers a unique platform for fundamental studies of highly non-linear soliton pair dynamics., (© 2024. The Author(s).)

The semiconductor industry is one of the most technology-evolving and capital-intensive market sectors. Effective inspection and metrology are necessary to improve product yield, increase product quality and reduce costs. In recent years, many types of semiconductor manufacturing equipments have been equipped with sensors to facilitate real-time monitoring of the production processes. These production-state and equipment-state sensor data provide an opportunity to practice machine-learning technologies in various domains, such as anomaly/fault detection, maintenance scheduling, quality prediction, etc. In this work, we focus on the soft-sensing regression problem in metrology systems, which uses sensor data collected during wafer processing steps to predict impending inspection measurements that used to be measured in wafer inspection and metrology systems. We proposed a regressor based on Long Short-term Memory network and devised two distinct loss functions for the purpose of the training model. Although the assessment of our prediction errors by engineers is subjective, a novel piece-wise evaluation metric was introduced to evaluate model accuracy in a mathematical way. Our experimental results showcased that the proposed model is capable of achieving both accurate and early prediction across various types of inspections in complicated manufacturing processes.

Magnons, the quantum-mechanical fundamental excitations of magnetic solids, are bosons whose number does not need to be conserved in scattering processes. Microwave-induced parametric magnon processes, often called Suhl instabilities, have been believed to occur in magnetic thin films only, where quasi-continuous magnon bands exist. Here, we reveal the existence of such nonlinear magnon-magnon scattering processes and their coherence in ensembles of magnetic nanostructures known as artificial spin ice. We find that these systems exhibit effective scattering processes akin to those observed in continuous magnetic thin films. We utilize a combined microwave and microfocused Brillouin light scattering measurement approach to investigate the evolution of their modes. Scattering events occur between resonance frequencies that are determined by each nanomagnet's mode volume and profile. Comparison with numerical simulations reveals that frequency doubling is enabled by exciting a subset of nanomagnets that, in turn, act as nanosized antennas, an effect that is akin to scattering in continuous films. Moreover, our results suggest that tunable directional scattering is possible in these structures., (© 2023. The Author(s).)

A three-dimensional self-consistent spin transport model is developed, which includes both tunnelling transport, leading to tunnelling magneto-resistance, as well as metallic transport, leading to giant magneto-resistance. An explicit solution to the drift-diffusion model is also derived, which allows analysing the effect of both the reference and free layer thickness on the spin-transfer torque polarization and field-like coefficient. It is shown the model developed here can be used to compute the signal-to-noise ratio in realistic magnetic read-heads, where spin torque-induced fluctuations and instabilities limit the maximum operating voltage. The effect of metallic pinhole defects in the insulator layer is also analysed. Increasing the area covered by pinholes results in a rapid degradation of the magneto-resistance, following an inverse dependence. Moreover, the spin torque angular dependence becomes skewed, similar to that obtained in fully metallic spin valves, and the spin-transfer torque polarization decreases. The same results are obtained when considering tunnel junctions with a single pinhole defect, but decreasing cross-sectional area, showing that even a single pinhole defect can significantly degrade the performance of tunnel junctions and magnetic read-heads below the 40 nm node., (© 2023 IOP Publishing Ltd.)

Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0-11.4% weight reduction, their specific Young's modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular "tiger-stripes" exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.

In this work, we propose exchange-coupled-composite-bit-patterned media (ECC-BPM) with microwave-assisted magnetic recording (MAMR) to improve the writability of the magnetic media at a 4 Tb/in 2 recording density. The suitable values of the applied microwave field's frequency and the exchange coupling between magnetic dots, A dot , of the proposed media were evaluated. It was found that the magnitude of the switching field, H sw , of the bilayer ECC-BPM is significantly lower than that of a conventional BPM. Additionally, using the MAMR enables further reduction of H sw of the ECC-BPM. The suitable frequency of the applied microwave field for the proposed media is 5 GHz. The dependence of A dot on the H sw was additionally examined, showing that the A dot of 0.14 pJ/m is the most suitable value for the proposed bilayer ECC-BPM. The physical explanation of the H sw of the media under a variation of MAMR and A dot was given. Hysteresis loops and the magnetic domain of the media were characterized to provide further details on the results. The lowest H sw found in our proposed media is 12.2 kOe, achieved by the bilayer ECC-BPM with an A dot of 0.14 pJ/m using a 5 GHz MAMR.

The current information technology has been developed based on von Neumann type computation. In order to sustain the rate of development, it is essential to investigate alternative technologies. In a next-generation computation, an important feature is memory potentiation, which has been overlooked to date. In this study, potentiation functionality is demonstrated in a giant magnetoresistive (GMR) junction consisting of a half-metallic Heusler alloy which can be a candidate of an artificial synapse while still achieving a low resistance-area product for low power consumption. Here the Heusler alloy films are grown on a (110) surface to promote layer-by-layer growth to reduce their crystallisation energy, which is comparable with Joule heating induced by a controlled current introduction. The current-induced crystallisation leads to the reduction in the corresponding resistivity, which acts as memory potentiation for an artificial GMR synaptic junction., (© 2021. The Author(s).)

Current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) read sensors based on Heusler alloys are promising candidates for ultrahigh areal densities of magnetic data storage technology. In particular, the thickness of reader structures is one of the key factors for the development of practical CPP-GMR sensors. In this research, we studied the dependence of the free layer thickness on the stability of the Co 2 (Mn 0.6 Fe 0.4 )Ge Heusler-based CPP-GMR read head for an areal density of 1 Tb/in 2 , aiming to determine the appropriate layer thickness. The evaluations were done through simulations based on micromagnetic modelling. The reader stability indicators, including the magnetoresistance (MR) ratio, readback signal, dibit response asymmetry parameter, and power spectral density profile, were characterized and discussed. Our analysis demonstrates that the reader with a free layer thickness of 3 nm indicates the best stability performance for this particular head. A reasonably large MR ratio of 26% was obtained by the reader having this suitable layer thickness. The findings can be utilized to improve the design of the CPP-GMR reader for use in ultrahigh magnetic recording densities.

Purpose: Magnetotransport properties of granular oxide-segregated CoPtCr films were studied on both macroscopic and microscopic length scales by performing bulk and point-contact magnetoresistance measurements, respectively. Such a perpendicular magnetic medium is used in state-of-the-art hard disc drives and, when combined with magnetotransport phenomena for read/write operations, may lead to a novel concept for magnetic recording with high areal density., Materials and Methods: The CoPtCr films were deposited by an epitaxy-like sputtering and contained several perpendicularly magnetized granular-media layers with different coercivities; they are very much like the state-of-the-art perpendicular magnetic medium, which can be found in today's hard disc drives. Magnetoresistive properties of bulk films were assessed by measuring the film resistance in the standard Van der Pauw geometry, while the local transport was probed by the point-contact technique., Results: The bulk measurements showed only a negligible magnetoresistance of less than 0.02%. In contrast, the local point-contact measurements revealed giant-magnetoresistance-like changes Δ R in local resistance of the contact R with more than 10,000% ratio Δ R/R ., Conclusion: The observed large and local magnetoresistive effect could be tentatively attributed to a tunnel magnetoresistance between oxide-segregated CoPtCr grains with different coercivities. The tunneling picture of electronic transport in our granular medium was confirmed by the observation of tunneling-like current-voltage characteristics of the contacts and bias dependence of the contact magnetoresistance - both the local point-contact resistance and magnetoresistance were found to decrease with the applied dc bias., Competing Interests: The authors report no conflicts of interest in conducting this work., (© 2021 Williamson et al.)

Magnetic nanoparticles have been proposed as contact-free minimal-background nanobarcodes, and yet it has been difficult to rapidly and reliably decode them in an assembly. Here, high aspect ratio nanoparticles, or magnetic nanowires (MNWs), are characterized using first-order reversal curves (FORC) to investigate quantitative decoding. We have synthesized four types of nanowires (differing in diameter) that might be used for barcoding, and identified four possible "signature" functions that might be used to quickly distinguish them. To test this, we have measured the signatures of several combination samples containing two or four different MNW types, and fit them to linear combinations of the individual type signatures to determine the volume ratios of the types. We find that the signature which determines the ratios most accurately involves only the slope of each FORC at its reversal field, which requires only 2-4 data points per FORC curve, reducing the measurement time by a factor of 10 to 50 compared to measuring the full FORC.

Optical Photothermal Infrared (O-PTIR) spectroscopy is a new technique for measuring submicron spatial resolution IR spectra with little or no sample preparation. This speeds up analysis times benefiting high-volume manufacturers through gaining insight into process contamination that occurs during development and on production lines. The ability to rapidly obtain far-field non-contact IR spectra at high spatial resolution facilitates the chemical identification of small organic contaminants that are not possible to measure with conventional Fourier transform infrared (FT-IR) microspectroscopy. The unique pump-probe system architecture also facilitates submicron simultaneous IR + Raman microscopy from the same spot with the same spatial resolution. With these unique capabilities, O-PTIR is finding utilization in the high-volume and high-value industries of high-tech componentry (memory storage, electronics, displays, etc.).

During the construction of recording head devices, corrosion of metal features and subsequent deposition of corrosion by-products have been observed. Previous studies have determined that the use of N-methylpyrrolidone (NMP) may be a contributing factor. In this study, we report the use of a novel multiplatform analytical approach comprising of pH, liquid chromatography/UV detection (LC/UV), inductively coupled plasma optical emission spectroscopy (ICP-OES), and LC/mass spectrometry (LC/MS) to demonstrate that reaction conditions mimicking those of general photoresist removal processes can invoke the oxidation of NMP during the photolithography lift-off process. For the first time, we have confirmed that the oxidation of NMP lowers the pH, facilitating the dissolution of transition metals deposited on wafer substrates during post-mask and pre-lift-off processes in microelectronic fabrication. This negatively impacts upon the performance of the microelectronic device. Furthermore, it was shown that, by performing the process in an inert atmosphere, the oxidation of NMP was suppressed and the pH was stabilized, suggesting an affordable modification of the photolithography lift-off stage to enhance the quality of recording heads. This novel study has provided key data that may have a significant impact on current and future fabrication process design, optimization, and control. Results here suggest the inclusion of pH as a key process input variable (KPIV) during the design of new photoresist removal processes., Competing Interests: All authors have declared no conflicts of interest., (Copyright © 2020 Gavin Lennon et al.)

The magnetic ground states in highly ordered double perovskites LaSr 1-x Ca x NiReO 6 (x = 0.0, 0.5, 1.0) are studied in view of the Goodenough-Kanamori rules of superexchange interactions in this paper. In LaSrNiReO 6 , Ni and Re sublattices are found to exhibit curious magnetic states separately, but no long range magnetic ordering is achieved. The magnetic transition at ~255 K is identified with the independent Re sublattice magnetic ordering. Interestingly, the sublattice interactions are tuned by modifying the Ni-O-Re bond angles through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction data reveals long range ferrimagnetic ordering of the Ni and Re magnetic sublattices along the crystallographic b-axis. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.

CoCrPt material is used for perpendicular magnetic recording media due to its high magneto-crystalline anisotropy that brings good thermal stability on the media. The addition of SiO 2 between the CoCrPt grains offers benefits including lower noise and better thermal stability. It has been reported that the SiO 2 content has strong effects on the media's recording performance such as coercivity, anisotropy and noise. In this work, we focus on studying the effects of the SiO 2 content on the nanomechanical properties of the media which are critical for the head-disk interface reliability. Variations of these properties with SiO 2 content provide guidelines for optimum designs considering both recording and mechanical interface performance.

The localized surface plasmon resonance (LSPR) sensitivity of metal nanostructures is strongly dependent on the interaction between the supporting substrate and the metal nanostructure, which may cause a change in the local refractive index of the metal nanostructure. Among various techniques used for the development of LSPR chip preparation, solid-state dewetting of nanofilms offers fast and cost effective methods to fabricate large areas of nanostructures on a given substrate. Most of the previous studies have focused on the effect of the size, shape, and inter-particle distance of the metal nanostructures on the LSPR sensitivity. In this work, we reveal that the silicon-based supporting substrate influences the LSPR associated refractive index sensitivity of gold (Au) nanostructures designed for sensing applications. Specifically, we develop Au nanostructures on four different silicon-based ceramic substrates (Si, SiO 2 , Si 3 N 4 , SiC) by thermal dewetting process and demonstrate that the dielectric properties of these ceramic substrates play a key role in the LSPR-based refractive index (RI) sensitivity of the Au nanostructures. Among these Si-supported Au plasmonic refractive index (RI) sensors, the Au nanostructures on the SiC substrates display the highest average RI sensitivity of 247.80 nm/RIU, for hemispherical Au nanostructures of similar shapes and sizes. Apart from the significance of this work towards RI sensing applications, our results can be advantageous for a wide range of applications where sensitive plasmonic substrates need to be incorporated in silicon based optoelectronic devices.

We report observation of a radial dependence in the magnetic anisotropy of epitaxially strained CoFe 2 O 4 nanopillars in a BaTiO 3 matrix. This archetypal example of a multiferroic heterostructure with a self-assembling three-dimensional architecture possesses significant out-of-plane uniaxial magnetic anisotropy. The anisotropy originates from the large magnetostriction of CoFe 2 O 4 and the state of stress within the nanocomposite. Magnetometry suggests the existence of two magnetic phases with different anisotropies. Micromagnetic simulations of a core-shell magnetic anisotropy qualitatively reproduce features of the magnetic hysteresis and elucidate the magnetization reversal mechanism: The magnetization initially reorients within the pillar core, followed by that of the shell. This is consistent with polarized small-angle neutron scattering which can be described by a CoFe 2 O 4 magnetization that is nonuniform on nanometer length scales. As the length scale of inhomogeneity of the magnetic anisotropy is similar to estimates of the relaxation of the displacement field from the CoFe 2 O 4 -BaTiO 3 interface, stress and its influence on structure provide an important route to new functionality of vertically aligned nanopillars for applications in low-power memory, computing, and sensing.

The science of system identification is widely utilized in modeling input-output relationships of diverse systems. In this article, we report field programmable gate array (FPGA) based implementation of a real-time system identification algorithm which employs forgetting factors and bias compensation techniques. The FPGA module is employed to estimate the mechanical properties of surfaces of materials at the nano-scale with an atomic force microscope (AFM). The FPGA module is user friendly which can be interfaced with commercially available AFMs. Extensive simulation and experimental results validate the design.

The directed self-assembly (DSA) and pattern transfer of poly(5-vinyl-1,3-benzodioxole-block-pentamethyldisilylstyrene) (PVBD-b-PDSS) is reported. Lamellae-forming PVBD-b-PDSS can form well resolved 5 nm (half-pitch) features in thin films with high etch selectivity. Reactive ion etching was used to selectively remove the PVBD block, and fingerprint patterns were subsequently transferred into an underlying chromium hard mask and carbon layer. DSA of the block copolymer (BCP) features resulted from orienting PVBD-b-PDSS on guidelines patterned by nanoimprint lithography. A density multiplication factor of 4× was achieved through a hybrid chemo-/grapho-epitaxy process. Cross-sectional scanning tunneling electron microscopy/electron energy loss spectroscopy (STEM/EELS) was used to analyze the BCP profile in the DSA samples. Wetting layers of parallel orientation were observed to form unless the bottom and top surface were neutralized with a surface treatment and top coat, respectively.

The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach.

The generation and control of fast switchable magnetic fields with large gradients on the nanoscale is of fundamental interest in material science and for a wide range of applications. However, it has not yet been possible to characterize those fields at high bandwidth with arbitrary orientations. Here, we measure the magnetic field generated by a hard-disk-drive write head with high spatial resolution and large bandwidth by coherent control of single electron and nuclear spins. We are able to derive field profiles from coherent spin Rabi oscillations close to the gigahertz range, measure magnetic field gradients on the order of 1 mT nm -1 and quantify axial and radial components of a static and dynamic magnetic field independent of its orientation. Our method paves the way for precision measurement of the magnetic fields of nanoscale write heads, which is important for future miniaturization of these devices.

The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO 2 -C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO 2 -C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

Materials with high volume magnetization are perpetually needed for the generation of sufficiently large magnetic fields by writer pole of magnetic hard disks, especially for achieving increased areal density in storage media. In search of suitable materials combinations for this purpose, we have employed density functional theory to predict the magnetic coupling between iron and gadolinium layers separated by one to several monolayers of 3d transition metals (Sc-Zn). We demonstrate that it is possible to find ferromagnetic coupling for many of them and in particular for the early transition metals giving rise to high moment. Cr and Mn are the only elements able to produce a significant ferromagnetic coupling for thicker spacer layers. We also present experimental results on two trilayer systems Fe/Sc/Gd and Fe/Mn/Gd. From the experiments, we confirm a ferromagnetic coupling between Fe and Gd across a 3 monolayers Sc spacer or a Mn spacer thicker than 1 monolayer. In addition, we observe a peculiar dependence of Fe/Gd magnetic coupling on the Mn spacer thickness.

We propose an internal (on-chip) Wheatstone bridge configuration to evaluate the efficiency of near-field transducers (NFT) as used in heat-assisted magnetic recording (HAMR). The electric field enhancement between the transducer and the image plane is monitored by measuring the resistance of metal electrodes composing the image plane. The absorption of the enhanced electric field causes an increase in the metal temperature, and thereby, in its resistance whose variation is monitored with an internal Wheatstone bridge which is accurately balanced in the absence of the electric field.