High-density Magnetic Storage Research Articles

Structural analysis, ferroic properties with enhanced magnetoelectric coupling in novel (1-x)BiFeO3-(x)GdFeO3 nanocomposites

Multiferroic composites exhibit substantially greater magnetoelectric interaction among order variables as compared to single-phase multiferroics, making them particularly attractive for futuristic multi-state RAM and spintronic gadgets. The multiferroic nanocomposites (1-x)BiFeO3-xGdFeO3 (x = 0.05, 0.10, 0.15, & 0.20) are synthesized by using solid-state route. The crystallographic and profile parameters are extracted from the dual-phase refinement of the rhombohedral (R3c) and orthorhombic (Pbnm) crystal structures. The optimized density, crystallite size and homogenous microstructure may be responsible for the improved dielectric and ferroic properties. TEM images reveal a reduction in the particle size (67–59 nm) upon GdFeO3 (GFO) loading. The HRTEM images unravel the interplanar spacing and associated Bragg planes, while the SAED rings validate the polycrystalline features of the samples. The high Curie temperature (Tc ̴ 643 °C) with enhanced specific heat (Cp ̴ 29.5 J/g°C) in x= 0.10 sample ensures its stable operation, efficient heat dissipation, minimal overheating, and greater thermal stability for reliable performance in demanding conditions. The surface and finite-size effects enhanced the magnetization (MS=1.04emu/g) in nanostructured ferromagnetic nanocomposite, making it a promising candidate for high-density magnetic storage devices and sensors. The high polarization (Pmax=8.39µC/cm2) and ME-coupling coefficient (αE=0.16mVcm−1Oe−1) observed in the most dense nanocomposite make it a potential candidate for magnetoelectric applications.

Convoluted Magnetoresistance and Magnetic Reversal Processes in Ni–Fe Segmented Cylindrical Nanodots with Tunable Size and Composition for Technological Applications

AbstractDue to their unique properties, bi‐segmented systems are currently used in several technological applications such as sensing devices, high density magnetic data storage systems, spintronics and microelectromechanical components, among others. In this study, the magnetoresistance and magnetic properties of Ni–Fe bi‐segmented cylindrical nanodots in a broad range of diameters and heights are discussed. The power of the First Principles approach, as considered in the density functional theory formulation, is used to study the structural and magnetic relaxation effects, and atomistic simulations, through the Fast Monte Carlo methodology, are employed to explore the magnetoresistance and magnetic behaviors of these systems. By means of the magnetic hysteresis and magnetoresistance signals, convoluted magnetization reversal schemes are discussed. These effects take place depending on the size of the Ni and Fe components as a result of the interplay among exchange interactions and size and shape effects induced by dipolar interactions. Since size has become an experimental controllable parameter, due to the enriched phenomena, the effects discussed in these bi‐component systems are useful for the design and production of devices for technological applications with relevance beyond the observed in the more restricted single component systems.

Design of Lanthanide Single-Chain Magnets Based on Tubular Segment Clusters

One-dimensional (1D) atomic chains that exhibit large magnetic anisotropy are highly relevant to spintronic applications. Such 1D magnetic systems have usually been produced by atom/molecular assembling on solid surfaces or by coordination polymers. Here, we demonstrate an alternative approach for the formation of a confined ferromagnetic holmium (Ho) atom chain, which is composed of repeating units of the tubular Ho doped boron (B) cluster HoB20. The tubular HoB20 is discovered by the global structural search of a series of small-sized boron clusters doped by a single Ho atom (HoBn, n = 12, 14, 16, 18, 20) using ab initio calculations. Electronic analysis reveals that the individual HoB20 cluster is stabilized by the double σ + π aromaticity. Extending the tubular structure results in a single Ho atom chain being confined inside a boron nanotube, which shows ferromagnetic behaviors and a large magnetic anisotropy of more than 40 meV/atom. Our findings indicate that the magnetic lanthanide chain is a promising candidate for high-density magnetic information storage.

FIRST-PRINCIPLES STUDY OF MAGNETIC ANISOTROPY ENERGY IN TWO-DIMENSIONAL FERROMAGNETIC CrI3

First-principles calculations are increasingly crucial in searching for new materials with customized properties or new functionality. First-principles calculations are superior in speed and cost, and comparable to experiments in terms of accuracy. Two-dimensional (2D) ferromagnetism materials were successfully fabricated experimentally in atomic thin films of CrI3. 2D intrinsic ferromagnetism with perpendicular magnetic anisotropy energy (PMAE) is an encouraging applicant compatible with high-density magnetic storage applications. In this study, spin density functional calculations are investigated on the magnetic anisotropy energy (MAE) in 2D monolayer ferromagnetic CrI3 using a first-principles electronic structure calculation. We include the MAE part calculation from the magnetocrystalline anisotropy energy (MCAE) that comes from the spin-orbit coupling (SOC). In the present calculation, the MCAE part, in addition to a usual scheme of total energy (TE), was evaluated using a grand-canonical force theorem (GCFT) scheme. The MCAE of 2D monolayer ferromagnetic CrI3 is 1.7 meV/unit cell and verified it has an easy-axis perpendicular to the crystal plane, which is a good agreement with experimental measurement. In the latter scheme, employing GCFT, we evaluated atom-resolved, k-resolved, and atomic k-resolved analyses for MCAE can be performed. From the GCFT result, the Cr atom indicates that it is the primary origin of PMAE in the atom-resolved MCAE. The negative MCAE contribution is in points, and the positive MCAE is mainly placed at the line in the 2D first Brillouin zone. Our systematic calculation in this work may also help design an effective structure of monolayer CrI3 in new 2D material magnetic sensor and spintronic device designs.

Structural characterization of ultrathin diamond-like carbon overcoats for high areal density magnetic recording

This paper reports a comprehensive study on chemical structures of ultrathin diamond-like carbon (DLC) overcoats for high areal density magnetic recording. The DLC overcoats were fabricated in a range of thicknesses between 0.5 and 5.0 nm with Si interlayer on NiFe substrates using a pulsed filtered cathodic vacuum arc (PFCVA) technique. The overcoat thicknesses were accurately determined by high–resolution transmission electron microscopy and wavelength dispersive X-ray fluorescence techniques. The surface morphology, chemical composition, microstructure, and tribological properties were systematically investigated by atomic force microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, Raman spectroscopy techniques, and a reciprocating wear test. The results showed that the surface morphologies of DLC overcoats were atomically smooth with a root mean square surface roughness below 0.23 nm. The DLC overcoats had high sp3 bonds fraction. However, as the overcoat thickness was thinner than 1 nm, the sp2 bonds fraction suddenly increased resulting in a significant increase in the coefficient of friction. The obtained results demonstrated the limitation of the thickness of the DLC overcoat fabricated by the PFCVA technique as a protective coating for high–density magnetic storage devices.

Co<sub>13</sub>Cu<sub>87</sub> and Fe<sub>3</sub>O<sub>4</sub> Nanoalloys for Ultrahigh Density Magnetic Storage

Being a part of a globalized society, we are using data at a truly unprecedented rate. Given the daily rise in the need for data and space consumption, it is clear that technology must be developed that will not only conserve space but also expand memory. Storage capacity is a key factor in the development of portable devices such as mobile, MP3 players, digital cameras, etc. In today's technology data storage capacity is crossing over its limit due to the superparamagnetic effect. This technology with longitudinal recording has an estimated limit of 100-200 gigabytes/sq.inch whereas, by perpendicular recording, it increases almost 100 times. This study involves analyzing magnetic single domain nanoparticles suitable for the purpose of high density magnetic data storage. In this work, Co13Cu87 and Fe3O4 have been studied and are speculated to perform satisfying performances. It has been shown that the magnetic characteristics of these nanoalloys can be easily tailored, making it versatile and scalable for storing data.

Magnetic anisotropy-controlled vortex nano-oscillator for neuromorphic computing

Chiral magnetic vortex has shown great potential for high-density magnetic storage, modern telecommunication and computation devices, thanks to its topological stability and rich dynamic behaviours. Particularly, the synchronization of magnetic vortex nano-oscillators leads to the emergence of fascinating collective phenomena used for microwave generator and neuromorphic computing. In this work, by means of micromagnetic simulations, we create stable chiral magnetic vortices by exploiting the chiral coupling principle and study the gyrotropic motion of the vortex core under spin-transfer torques. The gyrotropic oscillation frequency can be tuned by injecting spin-polarised current as well as the change of the magnetic anisotropy in the vortex area, resulting from the modification of the vortex confine potential and the size of the vortex core. Two vortex nano-oscillators can be synchronized wherein the synchronization state can be modulated by the spin-polarised current and the magnetic anisotropy. Moreover, we demonstrate that the magnetic anisotropy can modify the synchronization patterns when integrating six vortices into an oscillator network, making it potentially serve as an oscillator-based neural network. Our work provides a new route to constructing a flexible oscillator network for neuromorphic computing hardware.

Efficient perpendicular magnetization switching by a magnetic spin Hall effect in a noncollinear antiferromagnet

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows generation of the out-of-plane spin current carrying spin polarization collinear to its direction induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing the deterministic switching of the perpendicular magnetization of an adjacent Ni/Co multilayer. Due to being odd with respect to time reversal symmetry, the observed magnetic spin Hall effect and the resulting spin-orbit torque can be reversed with reversal of the antiferromagnetic order. Contrary to the conventional spin-orbit torque devices, the demonstrated magnetization switching does not need an external magnetic field and requires much lower current density which is useful for low-power spintronics.

Transition-Metal Interlink Neural Network: Machine Learning of 2D Metal-Organic Frameworks with High Magnetic Anisotropy.

Two-dimensional (2D) metal-organic framework (MOF) materials with large perpendicular magnetic anisotropy energy (MAE) are important candidates for high-density magnetic storage. The MAE-targeted high-throughput screening of 2D MOFs is currently limited by the time-consuming electronic structure calculations. In this study, a machine learning model, namely, transition-metal interlink neural network (TMINN) based on a database with 1440 2D MOF materials is developed to quickly and accurately predict MAE. The well-trained TMINN model for MAE successfully captures the general correlation between the geometrical configurations and the MAEs. We explore the MAEs of 2583 other 2D MOFs using our trained TMINN model. From these two databases, we obtain 11 unreported 2D ferromagnetic MOFs with MAEs over 35 meV/atom, which are further demonstrated by the high-level density functional theory calculations. Such results show good performance of the extrapolation predictions of TMINN. We also propose some simple design rules to acquire 2D MOFs with large MAEs by building a Pearson correlation coefficient map between various geometrical descriptors and MAE. Our developed TMINN model provides a powerful tool for high-throughput screening and intentional design of 2D magnetic MOFs with large MAE.

Strain-induced magnetic anisotropy of REIG thin films grown on YAG(111) substrates by pulsed laser deposition

Several studies have revealed using rare earth (RE) elements instead of yttrium to regulate the strain-induced magnetic anisotropy of garnet films in recent years. In this study, we used pulsed laser deposition to fabricate RE iron garnet (REIG) thin films on (111)-oriented yttrium aluminum garnet (YAG) substrates. The REIG films are 100 nm in thickness and crystalline with (111)-orientation. The out-of-plane (444)-plane spacing decreases as the ionic radius of RE metal ions decreases, while the crystallite size increases. Samarium, holmium, and yttrium iron garnet (SmIG, HoIG, and YIG) have out-of-plane compressive strain, while erbium and thulium iron garnet (ErIG and TmIG) have weak out-of-plane tensile strain. The strain of the REIG films is resulted from lattice mismatch, off-stoichiometry, and the recrystallization process by thermal annealing. SmIG has a rather rough surface because of the crystalline distortion due to the largest ionic radius of Sm and the lattice mismatch between SmIG and YAG substrates. Due to negative magnetostriction constant and out-of-plane compressive strain, SmIG and HoIG films show strong perpendicular magnetic anisotropy (PMA) in vibrating sample magnetometry and magneto-optical Faraday effect (MOFE). MOFE also revealed that the REIG films have different sensitivities at different wavelengths of light. With further tuning PMA on SmIG and HoIG by decreasing the thickness and lateral size, our findings could pave the way for high-density nano-scale magnetic information storage based on REIG thin films.

Effective modulating the electronic and magnetic properties of VI3 monolayer: A first-principles calculation

Exploring a two-dimensional ferromagnetic material with a high Curie temperature and large magnetic anisotropy energy is still challenging. Here, we implement an effective adjustment on the electronic and magnetic properties of VI 3 monolayer by means of first-principles calculation. The results indicate that the most stable structure of VI 3 monolayer is particularly susceptible to the calculation parameter such as Hubbard U and the spin-orbit coupling (SOC). Ultimately, under density functional theory (DFT) +U + SOC (U = 3 eV), the most stable structure of VI 3 monolayer is a ferromagnetic semiconductor with a direct band gap of 0.51 eV, and the predicted Curie temperature ( T C ) is 29 K. Biaxial strain and carrier doping could not only induce VI 3 monolayer FM-AFM-FM transition, but also effectively increase T C to 123 K under 0.5 electron doping. Meanwhile, carrier hoping realizes the potential ferromagnetic half-metal. Fortunately, in the constructing alloy monolayer, the VTaI 6 monolayer is found a ferromagnetic half-metal under DFT + U (U = 3, 1 eV for V and Ta), and the T C is increased to 74 K. Moreover, VTaI 6 monolayer possesses a large in-plane magnetic anisotropy energy (IMA) and its physical origin is explained in detail based on the second-order perturbation theory . These findings suggest that VI 3 monolayer has a potential application in the spintronics and high-density magnetic storage devices. • The most stable structure of VI 3 monolayer is very susceptible to the calculation parameters such as Hubbard U value and spin-orbit coupling effect. • Carrier doping can make the VI 3 system generate potential half-metallic characteristics, while biaxial strain maintains its semiconductor properties. • Biaxial strain and carrier doping could not only induce FM-AFM-FM transition, but also carrier doping make T C increase by 3–4 times. • The VTaI 6 monolayer is a FM half-metal and possesses a large in-plane magnetic anisotropy energy (−6.505 meV).

Coexisting ferromagnetic-antiferromagnetic state in twisted bilayer CrI3.

Moiré engineering1-3 of van der Waals magnetic materials4-9 can yield new magnetic ground states via competing interactions in moiré superlattices10-13. Theory predicts a suite of interesting phenomena, including multiflavour magnetic states10, non-collinear magnetic states10-13, moiré magnon bands and magnon networks14 in twisted bilayer magnetic crystals, but so far such non-trivial magnetic ground states have not emerged experimentally. Here, by utilizing the stacking-dependent interlayer exchange interactions in two-dimensional magnetic materials15-18, we demonstrate a coexisting ferromagnetic (FM) and antiferromagnetic (AF) ground state in small-twist-angle CrI3 bilayers. The FM-AF state transitions to a collinear FM ground state above a critical twist angle of about 3°. The coexisting FM and AF domains result from a competition between the interlayer AF coupling, which emerges in the monoclinic stacking regions of the moiré superlattice, and the energy cost for forming FM-AF domain walls. Our observations are consistent with the emergence of a non-collinear magnetic ground state with FM and AF domains on the moiré length scale10-13. We further employ the doping dependence of the interlayer AF interaction to control the FM-AF state by electrically gating a bilayer sample. These experiments highlight the potential to create complex magnetic ground states in twisted bilayer magnetic crystals, and may find application in future gate-voltage-controllable high-density magnetic memory storage.

Theoretical estimation of surface magnetic anisotropy on [formula omitted]-FePt thin films: Case of perfect and defect Surfaces.

We carried out first-principle calculations of magnetocrystalline anisotropy of L10-FePt thin films terminated by either perfect Fe (Pt) layers or defect surfaces, including vacancies or substituted surface atoms. Inspired by the experimental strategy for determining magnetic anisotropy, we present here a theoretical model for analyzing volume and surface magnetic anisotropies for L10-FePt thin films with different surface terminations. We demonstrate that surface anisotropy does not depend solely on the film thickness, but also on the atomic environment of the surface layer. Perpendicular surface anisotropy of L10-FePt thin films reaches its maximum with full Pt termination, which decreases with increasing Pt vacancies and becomes parallel to the surface for a full Fe surface. In the case of mixed surfaces, surface anisotropy of (3Pt,1Fe) is enhanced compared to platinum-rich surface with one vacancy, and tends to be more in-plane for an iron-rich surface (3Fe,1Pt). Our results could be used to study surface anisotropy effects on L10-FePt surfaces by mean of classical magnetic models, and they are very promising for the development of high density magnetic data storage such as magnetic memory.

Imaging of magnetic excitations in nanostructures with near-field microwave microscopy

We present images of spin-wave excitations in a patterned yttrium iron garnet (YIG) thin film obtained by use of near-field microwave microscopy, which can achieve spatial resolution as high as 50 nm. Visualization of magnetic excitations is an enticing prospect for high-speed, high-density magnetic logic and storage applications, which has spurred the development of new magnetic microscopy and imaging techniques in recent years. Here we present a novel approach for local imaging of magnetic modes excited at room temperature with sub-diffraction-limited spatial resolution. This approach is based on a special atomic force microscope with broadband GHz capability for imaging the spatial distribution of dynamic magnetic excitations in patterned magnetic structures. Due to the inherent sub-wavelength, nanometer-scale spatial resolution of near-field scanning probe techniques, this approach has potential for a significant improvement in spatial resolution over optical techniques.

Magnetization Reversal Process and Magnetostatic Interactions in Fe56Co44/SiO2/Fe3O4 Core/Shell Ferromagnetic Nanowires with Non-Magnetic Interlayer.

Nowadays, numerous works regarding nanowires or nanotubes are being published, studying different combinations of materials or geometries with single or multiple layers. However, works, where both nanotube and nanowires are forming complex structures, are scarcer due to the underlying difficulties that their fabrication and characterization entail. Among the specific applications for these nanostructures that can be used in sensing or high-density magnetic data storage devices, there are the fields of photonics or spintronics. To achieve further improvements in these research fields, a complete understanding of the magnetic properties exhibited by these nanostructures is needed, including their magnetization reversal processes and control of the magnetic domain walls. In order to gain a deeper insight into this topic, complex systems are being fabricated by altering their dimensions or composition. In this work, a successful process flow for the additive fabrication of core/shell nanowires arrays is developed. The core/shell nanostructures fabricated here consist of a magnetic nanowire nucleus (Fe56Co44), grown by electrodeposition and coated by a non-magnetic SiO2 layer coaxially surrounded by a magnetic Fe3O4 nanotubular coating both fabricated by means of the Atomic Layer Deposition (ALD) technique. Moreover, the magnetization reversal processes of these coaxial nanostructures and the magnetostatic interactions between the two magnetic components are investigated by means of standard magnetometry and First Order Reversal Curve methodology. From this study, a two-step magnetization reversal of the core/shell bimagnetic nanostructure is inferred, which is also corroborated by the hysteresis loops of individual core/shell nanostructures measured by Kerr effect-based magnetometer.

Spontaneous Topological Magnetic Transitions in NdCo5 Rare-Earth Magnets.

Particle-like magnetic textures with nanometric sizes, such as skyrmions, are potentially suitable for designing high-efficiency information bits in future spintronics devices. In general, the Dzyaloshinskii-Moriya interactions and dipolar interactions are the dominant factors for generating nonlinear spin configurations. However, to stabilize the topological skyrmions, an external magnetic field is usually required. In this study, the spontaneous emergence of skyrmions is directly observed, together with the unique successive topological domain evolution during the spin reorientation transition in a neodymium-cobalt (NdCo5 ) rare-earth magnet. On decreasing the temperature, nanometric skyrmion lattices evolve into enclosed in-plane domains (EIPDs) similar to mini bar-magnets with size below 120nm. The internal magnetization rotates with magnetic anisotropy, demonstrating the ability to manipulate the mini bar-magnets. The nanoscale EIPD lattices remain robust over the wide temperature range of 241-167 K, indicating the possibility of high-density in-plane magnetic information storage. The generation of spontaneous magnetic skyrmions and the successive domain transformation in the traditional NdCo5 rare-earth magnet may prompt application exploration for topological magnetic spin textures with novel physical mechanisms in versatile magnets.

Bimetal single-molecule magnets supported on benzene with large magnetic anisotropy and unquenched orbital moment

Single-atom magnets, the ultimate limit of high-density magnetic storage, have attracted widespread attention over recent decades. However, they are far from being applicable as a storage medium because of their low magnetic stability. In this paper, we describe a strategy to induce huge magnetic anisotropy in ``bimetal magnets'' on a benzene (Bz) substrate based on the electron filling of $d$ orbitals. Our first-principles calculations reveal that OsX-Bz ($X=\mathrm{Fe}$, Ru, and Os) exhibits high structural stability, large unquenched orbital moments ($1.55--1.59\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$), and huge perpendicular magnetic anisotropy energy (MAE) above 54.8 meV. The synergistic effect of two transition metal components toward this huge MAE and preserved orbital moment is discussed in depth, which is mainly attributed to the d-d coupling induced energy level rearrangement. Our work may provide insights into the underlying physical mechanism and bimetal molecule magnet design.

Nanoscale Magnetization and Current Imaging Using Time-Resolved Scanning-Probe Magnetothermal Microscopy.

Magnetic microscopy that combines nanoscale spatial resolution with picosecond scale temporal resolution uniquely enables direct observation of the spatiotemporal magnetic phenomena that are relevant to future high-speed, high-density magnetic storage and logic technologies. Magnetic microscopes that combine these metrics has been limited to facility-level instruments. To address this gap in lab-accessible spatiotemporal imaging, we develop a time-resolved near-field magnetic microscope based on magnetothermal interactions. We demonstrate both magnetization and current density imaging modalities, each with spatial resolution that far surpasses the optical diffraction limit. In addition, we study the near-field and time-resolved characteristics of our signal and find that our instrument possesses a spatial resolution on the scale of 100 nm and a temporal resolution below 100 ps. Our results demonstrate an accessible and comparatively low-cost approach to nanoscale spatiotemporal magnetic microscopy in a table-top form to aid the science and technology of dynamic magnetic devices with complex spin textures.

Nanostructured ZnFe2O4: An Exotic Energy Material

More people, more cities; the energy demand increases in consequence and much of that will rely on next-generation smart materials. Zn-ferrites (ZnFe2O4) are nonconventional ceramic materials on account of their unique properties, such as chemical and thermal stability and the reduced toxicity of Zn over other metals. Furthermore, the remarkable cation inversion behavior in nanostructured ZnFe2O4 extensively cast-off in the high-density magnetic data storage, 5G mobile communication, energy storage devices like Li-ion batteries, supercapacitors, and water splitting for hydrogen production, among others. Here, we review how aforesaid properties can be easily tuned in various ZnFe2O4 nanostructures depending on the choice, amount, and oxidation state of metal ions, the specific features of cation arrangement in the crystal lattice and the processing route used for the fabrication.

Zr6Co23 thin films grown on Al2O3(0001) substrate by RF magnetron sputtering: Correlation between the microstructural and magnetic properties

Zr6Co23 thin films deposited on Al2O3(0001) substrate by RF magnetron sputtering have been investigated. The effects of thickness δ on the magnetic properties are discussed using random magnetic anisotropy calculations and the ferromagnetic resonance measurements (FMR). Correlations between the microstructure, magnetic extrinsic and anisotropy properties, in particular the impacts of surface morphology and the roughness Rrms, exchange Aex, easy axis deviation θu° and magnetic anisotropy constants Ki,i=1,2, have been studied. The results showed that when the Zr6Co23 thickness was 150 nm, the Zr6Co23/Al2O3(0001) showed the optimum magnetic properties. The coercive field Hc = 172 × 104 A/m, maximum energy product (BH)max of 81.91 kJ/m3 and anisotropic field HA is around 9.31 × 104 A/m. The excellent properties of this film lead us to conclude that it is a very suitable candidate for spintronics and ultra high density magnetic storage applications.