High-density Magnetic Data Storage Research Articles

Using optical vortex laser induced forward transfer to fabricate a twisted ferrite microcrystal array

We demonstrate direct printing from donor ink containing ferrite nanoparticles by employing laser induced forward transfer with an optical vortex possessing orbital angular momentum (OAM). We show, for the first time, that the as-printed dots are twisted and exhibit spinel Fe3O4 monocrystalline properties without the need for a sintering process. The helicity of the as-printed dots is shown to be selectively controlled merely by reversing the handedness of optical vortices. The diameter of the printed dots was typically measured to be less than 1/10th of the irradiated laser spot (diffraction limit). These results imply that the optical vortex twists and confines the sintered nanoparticles within its dark core to form chiral spinel monocrystalline dots. The observation of mono-crystallization with optical vortex induced forward transfer will offer new fundamental physics such as OAM light–matter interactions and could pave the way toward advanced printable magnetic devices, such as high-density magnetic data storage.

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.

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.

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.

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.

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.

The effect of interstitial-site nitrogen on structural, elastic, and magnetic properties of face-center cubic Co

Cobalt plays a crucial role in the systematic understanding of magnetic phenomena originating from 3d transition metals. Particularly, recent studies of Co systems doped with nitrogen (Co–N) have attracted a lot of attention for applications in spintronics and high-density magnetic data-storage devices. In this work, in order to understand the effect of interstitial incorporation of N atoms into a face-center cubic (fcc) Co lattice, we have studied the structure, elastic, and magnetic properties of spherical-like bulk CoNx (x = 0.06–0.07) samples. These samples were synthesized through a high-pressure solid-state metathesis reaction. We demonstrate that the use of a certain concentration of interstitial N atoms tends to stabilize the lattice of fcc Co at ambient conditions. Such a stabilizing effect is found to originate from the covalent bond between Co atoms and N atoms. High-pressure synchrotron x-ray diffraction indicates that the incorporation of N atoms into fcc Co has little effect on the elastic property up to 27.2 GPa with a bulk modulus (B0) of 200 GPa; the latter is found to be comparable to that of fcc and hcp Co. CoNx samples exhibited ferromagnetic behavior with saturation magnetization up to 153.55 emu/g and coercivity of 16.25 Oe. The introduction of small amounts of nitrogen in the cobalt matrix was found to induce a significant decrease in the coercive force parameter.

Формирование пленок тройной системы CoNiFe электрохимическим осаждением

High-permeability films of CoNiFe triple system form the basis for high-density magnetic data storage. Electrochemical deposition of CoNiFe films, as contrasted with «dry» processes, gives more homogeneous coating with lesser defect level and allows reinforcing the films thickness without stresses. This study investigates the nature of the phenomena taking place at electrochemical deposition of CoNiFe films and leading to the difference in the relative content of the elements in the electrolyte and in the film. The hydrogen exponent of chloride electrolytes was examined in the temperature range of 25–70 °C and electrochemical deposition of CoNiFe films at 70 °C was studied. It was demonstrated that CoCl2, NiCl2, FeCl2 salt solutions with concentration from 0,006 to 1 mole/l are characterized by complex process of ion balance formation in single and mixed solutions. The deposition of CoNiFe films was carried out from chloride electrolyte with a component content ratio of 1:1:1 at an average concentration of 0,083 mole/l of each component. It has been established that the content of the component in the film at electrochemical deposition of three-component solution CoCl2, NiCl2, FeCl2 with equal concentration of each component did not correspond to the composition of the electrolyte but was closest to the composition of the electrolyte at a decrease in the concentration of each component at high current density.

Growth angle-dependent evolution of morphology and magnetic properties of Co films on highly ordered self-organized Ge substrates

This paper reports on the influence of growth angle on morphology and uniaxial magnetic anisotropy of 60 nm-thick sputter-deposited cobalt films on patterned-Ge substrates (having nanowire-like morphology with extreme regularity) prepared by keV-ion bombardment at room temperature. Morphological studies reveal that grain size in Co films increases with increasing growth angle, albeit lateral spacing among the ridges of conformally grown Co films (under growth angles in the range of 0–70°) on patterned-Ge substrates match quite well with that of a patterned-Ge substrate. While an increase in the Co grain size is expected to cause higher coercive fields, in the presence of magnetic pinning and slopes between ridges and grooves of nanowire-like patterned Co morphology, we observe an inverse trend. In other words, an increase in the grain size in conjunction with respective evolution of microstructures in Co films, at higher growth angles, lead to a decrease in the coercive field. Magnetic force microscopy is employed to probe the out-of-plane domains in ferromagnetic Co films. Tailored design of these novel nanostructured Co layers will be of interest for fabrication of high-density magnetic data storage devices, magneto-transport phenomena, and magneto-plasmonics.

Nanoscale control of stripe-ordered magnetic domain walls by vertical spin transfer torque in La0.67Sr0.33MnO3 film

Stripe-ordered domains with perpendicular magnetic anisotropy have been intensively investigated due to their potential applications in high-density magnetic data-storage devices. However, the conventional control methods (e.g., epitaxial strain, local heating, magnetic field, and magnetoelectric effect) of the stripe-ordered domain walls either cannot meet the demands for miniaturization and low power consumption of spintronic devices or require high strength of the electric field due to the small value of the magnetoelectric effect at room temperature. Here, a domain-wall resistive effect of 0.1% was clarified in La0.67Sr0.33MnO3 thin films between the configurations of current in the plane and perpendicular to the plane of walls. Furthermore, a reversible nanoscale control of the domain-wall re-orientation by vertical spin transfer torque across the probe/film interface was achieved, where a probe voltage of 0.1 V was applied on a manganite-based capacitor. We also demonstrated that the stripe-ordered magnetic domain-wall re-orientation strongly depends on the AC frequency of the scanning probe voltage which was applied on the capacitor.

Ultraslow waves on the nanoscale.

There has recently been a surge of interest in the physics and applications of broadband ultraslow waves in nanoscale structures operating below the diffraction limit. They range from light waves or surface plasmons in nanoplasmonic devices to sound waves in acoustic-metamaterial waveguides, as well as fermions and phonon polaritons in graphene and van der Waals crystals and heterostructures. We review the underlying physics of these structures, which upend traditional wave-slowing approaches based on resonances or on periodic configurations above the diffraction limit. Light can now be tightly focused on the nanoscale at intensities up to ~1000 times larger than the output of incumbent near-field scanning optical microscopes, while exhibiting greatly boosted density of states and strong wave-matter interactions. We elucidate the general methodology by which broadband and, simultaneously, large wave decelerations, well below the diffraction limit, can be obtained in the above interdisciplinary fields. We also highlight a range of applications for renewable energy, biosensing, quantum optics, high-density magnetic data storage, and nanoscale chemical mapping.

Zero-Point Spin-Fluctuations of Single Adatoms.

Stabilizing the magnetic signal of single adatoms is a crucial step toward their successful usage in widespread technological applications such as high-density magnetic data storage devices. The quantum mechanical nature of these tiny objects, however, introduces intrinsic zero-point spin-fluctuations that tend to destabilize the local magnetic moment of interest by dwindling the magnetic anisotropy potential barrier even at absolute zero temperature. Here, we elucidate the origins and quantify the effect of the fundamental ingredients determining the magnitude of the fluctuations, namely, the (i) local magnetic moment, (ii) spin-orbit coupling, and (iii) electron-hole Stoner excitations. Based on a systematic first-principles study of 3d and 4d adatoms, we demonstrate that the transverse contribution of the fluctuations is comparable in size to the magnetic moment itself, leading to a remarkable ≳50% reduction of the magnetic anisotropy energy. Our analysis gives rise to a comprehensible diagram relating the fluctuation magnitude to characteristic features of adatoms, providing practical guidelines for designing magnetically stable nanomagnets with minimal quantum fluctuations.

A novel magnetoelectric memory cell based on bilayer ferroelectric films of (1 − x)[Ba(Zr0.2Ti0.8)O3]–x(Ba0.7Ca0.3TiO3)

We demonstrate that a thin film magnetoelectric memory cell, comprised of Fe70Ga30 sputtered on top of bilayer ferroelectric films which consists of a tetragonal (T) 0.7Ba(Zr0.2Ti0.8)O3–0.3(Ba0.7Ca0.3TiO3) (70BZT–30BCT) film deposited on a rhombohedral (R) 0.3Ba(Zr0.2Ti0.8)O3–0.7(Ba0.7Ca0.3TiO3) (30BZT–70BCT) film. The insertion of rhombohedral layer improves the quality of the films and enhances the piezoelectric properties, which could be attributed to that the ferroelectric domains are tethered only by a soft R under layer, and not by the hard substrate. The working mechanism is that the 70BZT–30BCT layer acquires different strain states when an electric field is applied to it. Mechanical transduction couples this strain to the mechanically coupled Fe70Ga30 layer, which then changes its magnetic anisotropy and thus the magnetoresistance. The high (low) resistance states were realized when different voltages were applied due to the anisotropy magnetoresistance of Fe70Ga30 films. The demonstrated magnetoelectric memory device using resistance as the media and electric field as the writing field shows great promises towards exploring magnetoelectric devices for low-power and high density magnetic data storage applications.

Fabrication and characterization of a magnetoelectric memory cell of 50Ba(Zr0.2Ti0.8)O3–50Ba0.7Ca0.3TiO3/Fe70Ga30

We present a simple all-thin-film magnetoelectric memory cell with ferromagnetic film of Fe70Ga30 grown on ferroelectric film of 50Ba(Zr0.2Ti0.8)O3–50Ba0.7Ca0.3TiO3 (50BZT-50BCT) based on converse magnetoelectric effect. The heterostructure exhibits well-defined magnetic and piezoelectric behaviors. The 50BZT-50BCT layer acquires different strain states when an electric field is applied to the cell. Mechanical transduction couples this strain to the mechanically coupled Fe70Ga30 layer, which then changes its magnetic anisotropy and thus the magnetoresistance. Thus, a magnetoelectric memory cell with resistance as the media and electric field as the writing field was realized. The demonstrated electric field control of resistance states is a significant step towards exploring magnetoelectrically controlled spintronic devices for low-power and high density magnetic data storage applications.

Controlling the magnetic anisotropy of Ni cluster supported on graphene flakes with topological defects

Enhancing the magnetic anisotropy of transition metal (TM) clusters remains one of the primary objectives for applications of cluster assembled materials in high-density magnetic data storage devices. In this regard, graphene supports with topological disorder are considered as promising substrate materials for the TM clusters as defects can act as anchoring centers. Based on density functional theory for Ni clusters deposited on graphene nanoflakes, we show that magnetic anisotropy of Ni clusters can be tuned by specific topological defects in the graphene substrate. Systematic studies performed on pentagonal and heptagonal defects in graphene flakes show that Ni13 deposited on heptagonal defected graphene flake is a promising candidate with a large magnetic anisotropy energy of about ∼16 meV.

Graphyne as a promising substrate for high density magnetic storage bits

Applying magnetic nanostructures in high density magnetic data storage is hindered by a lack of suitable substrate.

Multiferroic composites for magnetic data storage beyond the super-paramagnetic limit

Ultra high-density magnetic data storage requires magnetic grains of <5 nm diameters. Thermal stability of such small magnetic grain demands materials with very large magneto-crystalline anisotropy, which makes data write process almost impossible, even when Heat Assisted Magnetic Recording (HAMR) technology is deployed. Here, we propose an alternative method of strengthening the thermal stability of the magnetic grains via elasto-mechanical coupling between the magnetic data storage layer and a piezo-ferroelectric substrate. Using Stoner-Wohlfarth single domain model, we show that the correct tuning of this coupling can increase the effective magneto-crystalline anisotropy of the magnetic grains making them stable beyond the super-paramagnetic limit. However, the effective magnetic anisotropy can also be lowered or even switched off during the write process by simply altering the applied voltage to the substrate. Based on these effects, we propose two magnetic data storage protocols, one of which could potentially replace HAMR technology, with both schemes promising unprecedented increases in the data storage areal density beyond the super-paramagnetic size limit.

Effect of electric-field on the perpendicular magnetic anisotropy and strain properties in CoFeB/MgO magnetic tunnel junctions

In this article, we investigate the effect of electric-field on the perpendicular magnetic anisotropy (PMA) and strain properties in nanoscaled CoFeB/MgO magnetic tunnel junction using tunnel magnetoresistance and piezoresponse force microscopy (PFM) measurements, respectively. We show that while the PMA change under electric-field is consistent with the previous reports, the PFM data show that the applied electric-field induces strain in a nanoscaled MgO. We demonstrate that the development of compressive and tensile strains corresponding to different polarities of applied electric-field. We discuss the interplay between the electric-field controlled PMA and strain properties. Our results may accelerate the development of magnetoelectrically controlled spintronic devices for low-power and high-density magnetic data storage applications.

Stabilizing the magnetic moment of single holmium atoms by symmetry

Single magnetic atoms, and assemblies of such atoms, on non-magnetic surfaces have recently attracted attention owing to their potential use in high-density magnetic data storage and as a platform for quantum computing. A fundamental problem resulting from their quantum mechanical nature is that the localized magnetic moments of these atoms are easily destabilized by interactions with electrons, nuclear spins and lattice vibrations of the substrate. Even when large magnetic fields are applied to stabilize the magnetic moment, the observed lifetimes remain rather short (less than a microsecond). Several routes for stabilizing the magnetic moment against fluctuations have been suggested, such as using thin insulating layers between the magnetic atom and the substrate to suppress the interactions with the substrate's conduction electrons, or coupling several magnetic moments together to reduce their quantum mechanical fluctuations. Here we show that the magnetic moments of single holmium atoms on a highly conductive metallic substrate can reach lifetimes of the order of minutes. The necessary decoupling from the thermal bath of electrons, nuclear spins and lattice vibrations is achieved by a remarkable combination of several symmetries intrinsic to the system: time reversal symmetry, the internal symmetries of the total angular momentum and the point symmetry of the local environment of the magnetic atom.

Switching the in-plane easy axis by ion implantation in rare earth based magnetic films

Ar+ ions have been implanted into Laves phase epitaxial thin films of YFe2 and DyFe2. Magneto-optical Kerr effect and vibrating sample magnetometry experiments show that the easy and hard axes of magnetization in both materials rotate through an in-plane angle of 90°, whilst the strength of the magnetic anisotropy remains unaltered. This is supported by OOMMF computational modelling. Atomic force microscopy confirms that the film roughness is not affected by implanted ions. X-ray diffraction data show that the lattice parameter expands upon ion implantation, corresponding to a release of strain throughout the entire film following implantation with a critical fluence of 1017 Ar+ ions cm−2. The anisotropy of the films is linked to the strain and from these data it is concluded that the source of anisotropy alters from one where magnetoelastic and magnetocrystalline effects compete to one which is governed solely by magnetocrystalline effects. The ability to locally tune the source of magnetic anisotropy without affecting the film surface and without inducing or eliminating anisotropy could be important in the fabrication of high density magnetic data storage media, spintronic devices and magneto-optical materials.