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In the literature, a magnetic "easy" axis perpendicular to the film plane at room temperature (i.e., perpendicular magnetic anisotropy - PMA) has been reported in Ni (nickel) layers with thicknesses below ≈15 nm. In this work, we observed room-temperature PMA in a-Si/Ni/a-Si (where a-Si denotes amorphous silicon) thin film structures with nickel layer thicker than 15 nm. Two layered structures were prepared by DC/RF triode sputtering: [a-Si/Ni/a-Si] sandwich structure and [a-Si/Ni/a-Si] 5 multilayer structure. The cross sectional STEM revealed uniform Ni layers with thicknesses of ≈17 nm in [a-Si/Ni/a-Si] 5 – multilayer and ≈28 nm in [a-Si/Ni/a-Si] – single-layer whereas amorphous Si layers were ≈15 nm and 170 nm thick, respectively. An amorphous Ni–Si interphase was also observed in the layered structures. The XRD showed patterns for fcc-Ni with dominant (111) orientation. No other crystalline phases were observed in the XRD patterns. To our knowledge, there are no literature reports of easy magnetization direction perpendicular to the film plane at room temperature for Ni layers with thickness of ≈28 nm as presented in this work. The origin of PMA in a-Si/Ni/a-Si films may be mainly attributed to the magnetoelastic anisotropy whereas the secondary source of PMA is believed to be the surface anisotropy and magnetocrystalline anisotropy of [111] columnar grains. Amorphous silicon layers (substrate) do not have a well-defined lattice structure like crystalline substrates. Therefore, they do not induce strains in the nickel layers through lattice mismatch as in the case of epitaxy. The strains can be caused by other factors such as diffusion-induced strain, thermal expansion mismatch or intrinsic stresses during the growth process. These results could be important for applications in memory devices, sensors, logic chips, magneto-optic, magneto-electronic and spintronic devices and in fundamental research, as well as first step toward preparation and understanding of the PMA in thick nickel layers. [ABSTRACT FROM AUTHOR]

Valley-spin hall (VSH) effect in monolayer WSe2 has been shown to exhibit highly beneficial features for nonvolatile memory (NVM) design. Key advantages of VSH-based magnetic random access memory (VSH-MRAM) over spin orbit torque (SOT)-MRAM include access transistor-less compact bit-cell and low-power switching of perpendicular magnetic anisotropy (PMA) magnets. Nevertheless, large device resistance in the read path ( $R_{S}$ ) due to low mobility of WSe2 and Schottky contacts deteriorates sense margin (SM), offsetting the benefits of VSH-MRAM. To address this limitation, we propose another flavor of VSH-MRAM that (while inheriting most of the benefits of VSH-MRAM) achieves lower $R_{S}$ in the read path by electrically isolating the read and write terminals. This is enabled by coupling VSH with electrically isolated but magnetically coupled PMA magnets via interlayer exchange coupling. Designing the proposed devices using object-oriented micromagnetic framework (OOMMF) simulation, we ensure the robustness of the exchange-coupled PMA system under process variations. To maintain a compact memory footprint, we share the read access transistor across multiple bit-cells. Compared with the existing VSH-MRAMs, our design achieves 39%–42% and 36%–46% reduction in read time and energy, respectively, along with $1.1\times - 1.3\times $ larger SM at a comparable area. This comes at the cost of $1.7\times $ and $2.0\times $ increase in write time and energy, respectively. Thus, the proposed design is suitable for applications in which reads are more dominant than writes.

To minimize the total film thickness and to make symmetric layer structures, the ultrathin symmetric Ta(1 nm)/Pt(1.7 nm)/ Co($t$)/Pt(1.7 nm)/Ta(1 nm) multilayers, where the Co thickness ($t$) was varied from 0.3 to 1.4 nm, were fabricated on Si substrate with a native oxide layer. The perpendicular magnetic anisotropy (PMA) was observed in the range of $t = 0.3-0.9$ nm. The coercive field of ~16 mT for $t =0.7$ nm and the domain wall velocity of ~ $100 \mu \text{m}$ /s for $t \le0.6$ nm were comparable with those in previous reports. Surprisingly, as the Co thickness approached 0.9 nm, the domain wall velocity dropped dramatically to ~ $0.1 \mu \text{m}$ /s, and the magnetic domain structure shifted from big-circular domains to small-bubble domains. A change from PMA to easy-plane magnetic anisotropy around $t =0.95$ nm could be explained using the classic Kittel’s model. Because of their good PMA, such ultrathin symmetric multilayers could be used in various spintronic applications. [ABSTRACT FROM AUTHOR]

• The HM/FM/XN design employs double interfacial effects on the PMA of the Pd/CMS/AlN/Pd multilayer structure. • Inserting AlN layer to Pd/CMS/Pd form Pd/CMS/AlN/Pd structure can increase R Hall by 300%, H c by 76% and K eff by 135%. • The PMA depends on the orbital hybridization effect of Pd5d-Co3d and Co3d-N2p electrons, and the crystallinity of each layer. In this paper, the perpendicular magnetic anisotropy（PMA）of Pd/Co 2 MnSi (CMS)/AlN/Pd multilayer film is studied, which is designed based on the two-interface interaction, the orbital hybridization effect of Pd5d-Co3d electrons at the Pd/CMS interface and the orbital hybridization effect of Co3d-N2p electrons at the CMS/AlN interface. Compared with the Pd/CMS/Pd multilayer film, the PMA of the Pd/CMS/AlN/Pd structure shows significant enhancement with the insertion of the AlN layer. The Hall resistance (R Hall) of the Pd/CMS/AlN/Pd structure reached 0.02 Ω (increased by 300 %) and the coercive force (H c) is 388 Oe (increased by about 76 %). The magnetic anisotropic energy density (K eff) is 0.61Merg/cm3 (increased by about 135 %). The PMA was optimized with the film factor (layer thickness) of Pd(6 nm)/CMS(5 nm)/AlN(6 nm)/Pd(6 nm). The X-Ray Diffraction（XRD）and High Resolution Transmission Electron Microscope（HRTEM）analysis showed that the PMA is affected by the crystallinity and interface quality of multilayer films. [ABSTRACT FROM AUTHOR]

In this study, Co/Pt based perpendicular synthetic antiferromagnetic (p-SAF) structures with Ru interlayers are investigated with regard to their magnetotransport properties. The p-SAF structures are varied in their number of Co/Pt multilayer (ML) stacks and Ru interlayers, and are examined for changes in their magnetoresistive effects. The alignment of magnetization directions of the MLs in the ML/Ru/ML stacks of the p-SAF generates a giant magnetoresistance effect (GMR), while the anisotropic magnetoresistance effect (AMR) at each ML further influences the resistance of the system. The GMR is found to increase linearly with the number of Ru interlayers. To extract contributions from the AMR, a simple model is proposed, which explains the observed transfer curves where both effects are taken into account. For the AMR amplitude, it is observed that longitudinal AMR contributions decrease with increasing numbers of Co layers in the p-SAF, whereas transverse components remain constant. While the highest GMR effects are measured at low temperatures, only longitudinal AMR contributions appear to be significantly affected by the measurement temperature. [ABSTRACT FROM AUTHOR]

Effects of the ferromagnetic layer thickness and annealing temperature were studied in Pt-/Co-/MgO-based systems grown on thermally oxidized Si substrates using magnetron sputtering system. The Co thicknesses were varied in the range of 1–6 nm and the samples were annealed ex situ at 200 °C, 300 °C, and 400 °C. Vibrating sample magnetometry was used to determine the magnetization at saturation and the magnetic dead layer thickness that were found to be insignificantly affected by the annealing. Brillouin light scattering, in Damon–Eshbach configuration, was used to measure the thermally excited spin wave (SW) frequencies versus the in-plane applied magnetic field and the SW vector which were used to investigate the perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii–Moriya interaction (iDMI), respectively. The Co effective thickness dependence of the effective magnetization ($M_{\mathrm {eff}}$), which provides information on the PMA constants, shows the existence of two linear regimes with different slopes due to misfit strain-induced magnetoelastic anisotropy contributions to volume and surface terms. The volume magnetocrystalline anisotropy constant increases monotonously with annealing temperature, whereas the pure surface (Néel type) constant increases with annealing up to 300 °C and degrades at 400 °C. The surface iDMI constant decreases with increasing annealing temperature and no obvious correlation with interface PMA constant has been found, suggesting different interfaces contribution to PMA and iDMI. [ABSTRACT FROM AUTHOR]

We have developed hard X-ray photoelectron spectroscopy (HAXPES) under an applied magnetic field of 1 kOe to study the electronic and magnetic states related to the MgO/Fe interface-induced perpendicular magnetic anisotropy (PMA). In this work, we used MgO (2 nm)/Fe (1.5 and 20 nm)/MgO(001) structures to reveal the interface-induced electronic states of the Fe film. Perpendicular magnetization of the 1.5-nm-thick Fe film without extrinsic oxidation of the Fe film was detected by the Fe 2p core-level magnetic circular dichroism (MCD) in HAXPES under a magnetic field, and easy magnetization axis perpendicular to the film plane was confirmed by ex situ magnetic hysteresis measurements. The valence-band HAXPES spectrum of the 1.5-nm-thick Fe film revealed that the Fe 3d electronic states were strongly modified from the thick Fe film and a reference bulk Fe sample due to the lifting of degeneracy in the Fe 3d states near the MgO/Fe interface. We found that the tetragonal distortion of the Fe film by the MgO substrate also contributes to the lifting of degeneracy in the Fe 3d states and PMA, as well as the Fe 3d-O 2p hybridization at the MgO/Fe interface, by comparing the valence-band spectrum with density functional theory calculations for MgO/Fe multilayer structures. Thus, we can conclude that the Fe 3d-O 2p hybridization and tetragonal distortion of the Fe film play important roles in PMA at the MgO/Fe interface. HAXPES with in situ magnetization thus represents a powerful new method for studying spintronic structures.

Magnetoresistive (xMR) sensors find extensive application in science and industry, replacing Hall sensors in various low field environments. While there have been some efforts in increasing the dynamic field range of xMR sensors, Hall sensors remain to dominate high field applications due to their wide linear range. Using a perpendicularly magnetized reference system and an in-plane free layer allows us to overcome this disadvantage of xMR sensors, and, furthermore, investigate spin-canting effects in interlayer exchange coupled perpendicular synthetic antiferromagnets (p-SAF). We achieved p-SAFs with exchange coupling fields of up to 10kOe, based on magnetic Co/Pt multilayer systems. The p-SAFs are either designed as “single” p-SAFs, where two Co/Pt multilayers are interlayer exchange coupled via a 4Å thick Ru spacer, or as “double” p-SAFs, where an additional Co layer is interlayer exchange coupled to the top multilayer. These p-SAFs are used for giant magnetoresistance (GMR) sensors with wide dynamic field range, limited only by the p-SAF’s switching fields. Additionally, the magnetic anisotropy of the in-plane free layer is fully controlled, which allows saturation fields by design. With this, the entire spectrum from parallel to antiparallel alignment of free and reference layer is exploited, which yields the full GMR signal potential. We discovered through micromagnetic simulations that certain GMR transfer curves are dominated by spin-canting effects in the interlayer exchange coupled reference system. Finally, our simulation results lay out the correlation of the p-SAF’s design parameters and its magnetization reversal behavior. [ABSTRACT FROM AUTHOR]

Ab initio calculations of voltage-controlled perpendicular magnetic anisotropy predict that the adjunction of Pt at the top of Co/MgO interface in Pt/Co/MgO ultrathin structures would enhance the perpendicular anisotropy and its electric field (E-field) variation rate. Following these theoretical expectations, using the magnetron-sputtering technique, we first designed and elaborated magnetic multilayered samples which have subsequently been patterned by UV lithography in magnetotransport devices. The as-deposited samples show perpendicular magnetization configuration whose E-field modulation has been studied by anomalous Hall effect magnetometry experiments under applied E-field in patterned devices. The measured voltage anisotropy modulation effect is found to be asymmetric with respect to the E-field polarity, in qualitative agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

A spin valve structure comprising two free layers based on skyrmion with perpendicular magnetic anisotropy (PMA) and a vortex with in-plane magnetic anisotropy (IMA) is investigated using micromagnetic simulation methods. The investigation reveals an interfacial Dzyaloshinskii–Moriya (DM) exchange interaction between the layers, leading to the transfer of DM energy from the skyrmion to the vortex layer, resulting in an increased frequency of vortex core oscillation. Also, the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between IMA and PMA layers induces magnetization oscillations with increased amplitude. The hybrid polarizer's dimensions, current density, IMA layer thickness, DM field strength, bilinear surface exchange energy coefficient, and damping coefficient can be adjusted to manipulate this effect. This structure holds promising potential for generating robust oscillations with an increased frequency of vortex core gyration, facilitated by the DM and RKKY interactions; moreover, the integration of skyrmion and vortex presents a novel approach to controlling magnetic properties in nanoscale devices. • A spin valve nanopillar with IMA/PMA layers. • Enhanced DM exchange boosts vortex core oscillation frequency. • RKKY interaction induces amplified magnetization oscillations. • Potential for Spin Torque Nano Oscillators (STNOs). [ABSTRACT FROM AUTHOR]

Magnetic interlayer coupling is a critical study topic for spintronic device technology because it is an essential component in designing magnetic multilayers with functionality that can be expanded into application areas. Particularly, the interlayer coupling between two ferromagnetic (FM) layers with different magnetic properties in the magnetic field is the specific situation to develop spintronic applications, such as increasing the sensitivity of magnetic field sensors. Therefore, the film structure was chosen as two layers in this study; the first ferromagnetic layer (FM 1 -CoRh) has a perpendicular and the second ferromagnetic layer (FM 2 -Fe) has an in-plane (IP) magnetic easy axis in the presence of a magnetic field. Here, a non-magnetic (NM) Rh spacer layer separated the two FM layers. The magnetic properties dependent on spacer layer thickness (t) in CoRh/Rh/Fe multilayers were investigated in detail. It is found that the strength of interlayer coupling alters depending on the t. [ABSTRACT FROM AUTHOR]

Spin-orbit torque (SOT) is a promising switching mechanism for magnetic random-access memory (MRAM) as a result of the potential for improved switching speed and energy efficiency. It is of particular interest to develop an SOT-MRAM device with perpendicular magnetic anisotropy (PMA) in order to leverage the greater density and thermal stability achievable with PMA as opposed to in-plane magnetic anisotropy. However, the orthogonality between SOT and PMA prevents deterministic directional switching without an additional device component that breaks the symmetry, such as an external magnetic field or complex physical structure; not only do these components complicate fabrication, they also are not robust to variations in fabrication and applied switching current. Following previous work demonstrating toggle SOT switching of ferromagnetic layers, this article, therefore, proposes a simple SOT-MRAM structure with PMA in which deterministic toggle switching is achieved without requiring additional device components. Furthermore, this toggle PMA SOT-MRAM is shown to be far more robust than previous approaches for directional PMA SOT-MRAM, with no maximum current pulse duration and greater than 50% tolerance to applied switching current magnitude. This article describes the physical structure and toggle switching mechanism, provides micromagnetic simulations demonstrating its feasibility, and evaluates the robustness and tolerance to material parameters to guide the fabrication of optimized devices that will jumpstart the third generation of MRAM.

We study the impact of irradiation on magnetic tunnel junction (MTJ) films with perpendicular magnetic anisotropy (PMA) and spin–orbit torque (SOT) switching using magneto-optical Kerr effect and transmission electron microscopy. Our results show that the thin-film stack is robust to gamma ionizing dose up to 1 Mrad(Si) and Ta1+ ion irradiation fluences up to 1012 ions/cm2, showing SOT PMA MTJs are radiation-hard. But, at very high Ta1+ ion irradiation between 1012 and 1014 ions/cm2, reduced coercivity and eventually greatly reduced PMA are observed, corresponding with an increase in intermixing of the CoFeB–MgO layers, particularly at the lower CoFeB–MgO interface. These results agree with displacement damage modeling that predicts higher damage in the layers closer to the bottom heavy metal and substrate. Compared to spin transfer torque and in-plane anisotropy MTJs, needing a top-pinned stack, a thicker heavy metal layer, and perpendicular anisotropy that is pinned out of plane by interfaces, all could make SOT PMA MTJs more susceptible to damage at high doses. [ABSTRACT FROM AUTHOR]

We evaluate the resilience of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) to displacement damage induced by heavy-ion irradiation. MTJs were exposed to 3-MeV Ta2+ ions at different levels of ion beam fluence spanning five orders of magnitude. The devices remained insensitive to beam fluences up to $10^{11}$ ions/cm2, beyond which a gradual degradation in the device magnetoresistance, coercive magnetic field, and spin-transfer-torque (STT) switching voltage were observed, ending with a complete loss of magnetoresistance at very high levels of displacement damage (>0.035 displacements per atom). The loss of magnetoresistance is attributed to structural damage at the MgO interfaces, which allows electrons to scatter among the propagating modes within the tunnel barrier and reduces the net spin polarization. Ion-induced damage to the interface also reduces the PMA. This study clarifies the displacement damage thresholds that lead to significant irreversible changes in the characteristics of STT magnetic random access memory (STT-MRAM) and elucidates the physical mechanisms underlying the deterioration in device properties. [ABSTRACT FROM AUTHOR]

We investigate the ferromagnetic resonance (FMR) response of thin NixCoyPd1–x–y alloy films. An FMR shift similar to Co–Pd alloy thin films is found in the presence of hydrogen gas in the sample environment. We find that the measured change in effective magnetization has an exponential dependence on the Pd concentration in the alloy. Additionally, we find a sudden decrease in sensitivity to hydrogen for low hydrogen concentrations. [ABSTRACT FROM AUTHOR]

Perpendicular magnetic anisotropy (PMA) of magnets is paramount for electrically controlled spintronics due to their intrinsic potentials for higher memory density, scalability, thermal stability and endurance, surpassing an in-plane magnetic anisotropy (IMA). Nickel film is a long-lived fundamental element ferromagnet, yet its electrical transport behavior associated with magnetism has not been comprehensively studied, hindering corresponding spintronic applications exploiting nickel-based compounds. Here, we systematically investigate the highly versatile magnetism and corresponding transport behavior of nickel films. As the thickness reduces within the general thickness regime of a magnet layer for a memory device, the hardness of nickel films' ferromagnetic loop of anomalous Hall effect increases and then decreases, reflecting the magnetic transitions from IMA to PMA and back to IMA. Additionally, the square ferromagnetic loop changes from a hard to a soft one at rising temperatures, indicating a shift from PMA to IMA. Furthermore, we observe a butterfly magnetoresistance resulting from the anisotropic magnetoresistance effect, which evolves in conjunction with the thickness and temperature-dependent magnetic transformations as a complementary support. Our findings unveil the rich magnetic dynamics and most importantly settle down the most useful guiding information for current-driven spintronic applications based on nickel film: The hysteresis loop is squarest for the ∼8 nm-thick nickel film, of highest hardness with R xy r / R xy s ∼ 1 and minimum H s - H c , up to 125 K; otherwise, extra care should be taken for a different thickness or at a higher temperature., (© 2024 IOP Publishing Ltd.)

We report the magnetic properties of yttrium iron garnet (YIG) thin films grown by pulsed laser deposition technique. The films were deposited on Si (100) substrates in the range of 15–50 nm thickness. Magnetic characterizations were investigated by ferromagnetic resonance spectra. Perpendicular magnetic easy axis was achieved up to 50 nm thickness. We observed that the perpendicular anisotropy values decreased by increasing the film thickness. The origin of the perpendicular magnetic anisotropy (PMA) was attributed to the texture and the lattice distortion in the YIG thin films. We anticipate that perpendicularly magnetized YIG thin films on Si substrates pave the way for a cheaper and compatible fabrication process. [ABSTRACT FROM AUTHOR]

We have developed hard X-ray photoelectron spectroscopy (HAXPES) under an applied magnetic field of 1 kOe to study the electronic and magnetic states related to the MgO/Fe interface-induced perpendicular magnetic anisotropy (PMA). In this work, we used MgO (2 nm)/Fe (1.5 and 20 nm)/MgO(001) structures to reveal the interface-induced electronic states of the Fe film. Perpendicular magnetization of the 1.5-nm-thick Fe film without extrinsic oxidation of the Fe film was detected by the Fe 2p core-level magnetic circular dichroism (MCD) in HAXPES under a magnetic field, and easy magnetization axis perpendicular to the film plane was confirmed by ex situ magnetic hysteresis measurements. The valence-band HAXPES spectrum of the 1.5-nm-thick Fe film revealed that the Fe 3d electronic states were strongly modified from the thick Fe film and a reference bulk Fe sample due to the lifting of degeneracy in the Fe 3d states near the MgO/Fe interface. We found that the tetragonal distortion of the Fe film by the MgO substrate also contributes to the lifting of degeneracy in the Fe 3d states and PMA, as well as the Fe 3d-O 2p hybridization at the MgO/Fe interface, by comparing the valence-band spectrum with density functional theory calculations for MgO/Fe multilayer structures. Thus, we can conclude that the Fe 3d-O 2p hybridization and tetragonal distortion of the Fe film play important roles in PMA at the MgO/Fe interface. HAXPES with in situ magnetization thus represents a powerful new method for studying spintronic structures. [ABSTRACT FROM AUTHOR]

We present a synthesis/processing method for fabricating ferrimagnetic insulator (Bi-doped yttrium iron garnet) thin films with tunable magnetic anisotropy. Since the desired magnetic properties rely on controllable thickness and successful doping, we pay attention to the entire synthesis/processing procedure (nanopowder synthesis, nanocrystalline target preparation and pulsed laser deposition (PLD)). Atomically flat films were deposited by PLD on (111)-orientated yttrium aluminum garnet. We show a significant enhancement of perpendicular anisotropy in the films, caused by strain-induced anisotropy. In addition, the perpendicular anisotropy is tunable by decreasing the film thickness and overwhelms the shape anisotropy at a critical thickness of 3.5 nm.

• The effects of Nb buffer on the PMA of Nb/CoFeB/MgO/Ta films have been studied. • The composition–structure–property relationships of the films were studied. • The crystallized layers, forming oxide and smooth interface all contributed to PMA. The effects of Nb buffer layers on the magnetic properties of Nb/CoFeB/MgO/Ta films have been studied. The films exhibited perpendicular magnetic anisotropy (PMA) when the Nb buffer layer thickness approached or exceeded 3 nm. PMA was retained at annealing temperatures up to 350 °C for the films containing 5-nm Nb buffer layer. The Ta, CoFeB, MgO, and Nb layers were easily distinguished by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy showed that the Nb, MgO, CoFeB, and Ta layers were crystalline. X-ray photoelectron spectroscopy indicated that the oxygen reduced from MgO combined with Fe and Co to form FeO x and CoO x after annealing, strengthening the PMA. The Nb(5)/CoFeB(1)/MgO(2)/Ta(3) film exhibited a smooth CoFeB/MgO interface after annealing, as confirmed by X-ray reflectivity. The crystallized MgO and CoFeB, formation of Fe and Co oxides, and smooth CoFeB/MgO interface all contributed to the strong PMA. [ABSTRACT FROM AUTHOR]

Pt\Co\W multilayers are evaluated as a novel material composition for the use in perpendicular nanomagnetic logic (pNML) applications. Starting from single and bilayer stacks, the material system is explored for maximum Co thicknesses while preserving perpendicular magnetic anisotropy (PMA) as well as single-domain behavior for micrometer-sized structures. Results for single trilayers show significantly reduced saturation magnetizations when compared to Pt\Co\Pt. Anisotropy measurements reveal a comparable volume component together with substantially reduced surface contributions. The subsequent analysis of [Co 1.22 \Pt 1.45 \W X ] 2 bilayer stacks indicates the emergence of weak interlayer coupling superposed by anisotropy differences, for Tungsten thicknesses t W ⩾ 0.5 nm , not exceeding the low mT range. The impact of local anisotropy engineering on micro-magnetic test structures by means of Ga + ion beam irradiation for different stack compositions is investigated, targeting low nucleation fields and shaping hysteresis behaviors for single step switching. First operational dipole-coupled inverter structures based on a Pt\Co\Heavy-Metal system are demonstrated achieving clocking fields down to 50 mT. [ABSTRACT FROM AUTHOR]

We report the directed transport of superparamagnetic microbeads (SPBs) on antidot arrays patterned from multilayered Co/Pt films with perpendicular magnetic anisotropy (PMA). The dynamics of water-suspended SPBs driven across the substrate surface by elliptical rotating magnetic fields is studied experimentally and modeled analytically. Bead motion on PMA substrates is shown to be significantly faster than on similarly patterned films based on in-plane magnetized materials. Furthermore, we show different SPB trajectories on different lattice geometries, suggesting that the magnetic potential distribution plays a crucial role in determining the dynamics. Our findings provide new insights into the enhanced transport of SPBs using PMA thin films as stray field sources that enable dynamic magnetic potential landscapes. [ABSTRACT FROM AUTHOR]

We investigated the effect that Ta spacer had on the interfacial microstructures and magnetic properties of MgO/CoFeB/Ta/CoFeB/MgO films. We found that when the Ta spacer thickness was optimized, the double MgO interface led to an enhancement in the perpendicular magnetic anisotropy (PMA) and thermostability. By systematically studying the changes for different structures in the chemical state, we interpreted how elements diffuse and alter the chemical states and properties of the magnetic tunnel junctions (MTJs). We found that increasing the Fe oxide is crucial to the PMA in the films and we attribute the increase in the of Fe oxide content to the oxygen liberated by the reduction of boron oxide. • The magnetic properties and thermal stability of MgO/CoFeB/Ta/CoFeB/MgO films were studied. • Fe oxide was increased through the oxygen liberated by the reduction of boron oxide. • The formation of minor Fe(Co)oxide at the CoFeB/MgO interface enhanced the PMA. [ABSTRACT FROM AUTHOR]

Highlights • The evolution of PMA in Ta/MgO/CoFeB/W/CoFeB/MgO/Ta annealed for different temperature is reported. • The composition-structure-property relationships in Ta/MgO/CoFeB/W/CoFeB/MgO/Ta is studied. • The oxygen released by WOx and MgO combined with Fe and Co, thereby more Fe or Co oxides were formed. Abstract In Magnetic tunnel junctions, which are applied in spintronic devices, the key issue is low thermal stability. Here, we study the influence of a W spacer on the perpendicular magnetic anisotropy (PMA) at temperatures up to 525 °C in perpendicular magnetized MgO/CoFeB/MgO structures with thin W spacer. High-resolution transmission electron microscopy (HRTEM) analysis shows that the MgO layers are partially crystallized and a significant diffusion of the small number of W elements is detected. The X-ray photoelectron spectroscopy (XPS) indicates that some WO x compounds were reduced to metallic W and part of MgO were reduced to Mg during annealing. The oxygen released by WO x and MgO combined with Fe and Co, thereby more Fe and Co oxides were formed and thus benefiting the perpendicular magnetic anisotropy (PMA). [ABSTRACT FROM AUTHOR]

Magnetization studies were carried out on Tb–Fe and Tb–Fe–Co thin films, prepared using magnetron co-sputtering technique. The films Tb25Fe75 and Tb31Fe69 were found to have perpendicular magnetic anisotropy (PMA) both at 25 and 300 K. In Tb–Fe–Co films, all the films were observed to exhibit planar anisotropy at 25 K, due to the increase of strain-induced anisotropy as a result of large magnetostriction at low temperatures leading to the development of in-plane anisotropy. PMA was observed in the films Tb35Fe37Co28, Tb56Fe25Co19, and Tb63Fe20Co17 at 300 K. The Curie temperatures (TC) of both TbxFe100–x and Tb–Fe–Co films were found to be above room temperature (RT). Observing the Curie temperatures well above the RT, with the existence of PMA at RTs, is an interesting object in these films to find in magnetic data storage applications. [ABSTRACT FROM AUTHOR]

Herein, using first-principles calculations, we explore the magnetic-phase order and magnetic anisotropy energy (MAE) of FeRh (001) films with different heavy transition-metal contact layers (HTM = Hf, Ta, and W). While the antiferromagnetic ground state of FeRh still persists at the W/FeRh interface with the thicker FeRh films, the earlier HTMs of Hf and Ta favor the robust ferromagnetism in the interfacial FeRh layers. Moreover, in contrast to an in-plane magnetization of W/FeRh bilayer, the magnetization direction of FeRh reorients from in-plane to perpendicular in the presence of Hf and Ta overlayers. In particular, a large perpendicular MAE of 2 meV is identified at the Hf/FeRh interface, which is associated with the interfacial magnetic-phase transition and the large spin-orbit coupled 3d–5d hybridization. [ABSTRACT FROM AUTHOR]

We have studied the structure and the magnetic properties of CoPt films by using TiN spacer layer deposited on a glass substrate. We show that after annealing at 700 °C, a highly (001)-textured L10 CoPt structure has been successfully obtained. However, by increasing the annealing temperature to 800 °C, two magnetic phases A1 CoPt and L10 CoPt are formed despite of the better crystallinity of CoPt than that annealed at 700 °C. By measuring the minor magnetic hysteresis loops of the samples after applying a field cooling in a range from room temperature to 500 °C, we have further studied the magnetic coupling between A1 and L10 CoPt phases in the out-of-plane direction of the films. Our work may provide a piece of information for other studies on the heat-assisted magnetic recording. [ABSTRACT FROM AUTHOR]

With the inception of perpendicular magnetic anisotropy-based magnetic tunnel junction (PMTJ) devices, spin-transfer torque (STT) magnetic random access memory (MRAM) is considered as a promising candidate for low power high-density embedded memory applications. However, the single-level cell STT-MRAM did not create much impact due to its energy/area inefficiency, higher cost per bit, and unoptimized read/write operations in sub-50 nm regime. In this paper, a series multilevel cell (sMLC) STT-MRAM is proposed that offers higher array density with reliable and energy efficient read–write operations with minimum error rates at the lower supply voltage. A high-k dielectric metal gate-based gate-all-around vertical silicon nanowire is used to drive the sMLC. A unified model based on Verilog-A and HSPICE is employed to imitate the PMTJ device. The results of 2 bit sMLC designs demonstrate switching error probability much below $10^{-9}$ , and average write energy <2 pJ at the pulsewidth of 20 ns with a footprint area of 2F2 per bit (F is the feature size). [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) based on MgO/CoFeB/W structures are of particular interest for magnetic random access memories due to their high tunnel magnetoresistance, low damping, and stable properties at high annealing temperature. One of the major challenges is to obtain a strong interfacial perpendicular magnetic anisotropy (PMA) for sufficient thermal stability during data storage. Here we investigate magnetic anisotropy energies (MAEs) in the ferromagnet (FM)/W structure with different FM materials and interface insertions. We find that the Fe/W interface exhibits a remarkable PMA, whereas the Co/W interface displays a large in-plane anisotropy, which reduces the PMA in the MgO/CoFeB/W structure. By inserting a thin Fe layer at the CoFe/W interface, the interfacial PMA can be enhanced to 3.34 mJ/m2. Microscopic mechanism behind these phenomena is explained with the changes of orbital-resolved MAEs due to the charge redistribution at the interface. These findings pave a new way for the enhancement of PMA and point toward the possibility of achieving high thermal stability in small-node MTJs. [ABSTRACT FROM AUTHOR]

In this paper, we carry out a detailed investigation of a recently discovered effect of the increase in the ferromagnetic resonance (FMR) amplitude for cobalt–palladium layered films in the presence of hydrogen gas (H2). We find that this effect is not correlated with the FMR peak shift in the presence of H2 found previously. This follows from observation of a vanishing shift but a change in the amplitude of 69.5% for a sample having a 70 nm thick cobalt layer studied in this paper. The change in amplitude is found to be mainly due to the narrowing of the FMR linewidth, which has its origin in a change in the damping parameter $\alpha $. The increase in the amplitude allows us to measure H2 concentration in nitrogen as a carrier gas in a very broad range—from 0.05% to 70% with sensitivity higher than in our previous papers. [ABSTRACT FROM AUTHOR]

In this paper, the anomalous Hall effect (AHE) of [Fe2CoSi/Pt]n multilayers with large perpendicular magnetic anisotropy has been investigated. We found that both skew scattering (SS) and side jump contribute to the AHE, while SS is the dominant contribution to the AHE. Moreover, the contribution of SS to the AHE becomes less significant when either decreasing the thickness of Pt layer or increasing the number of periods $n$. [ABSTRACT FROM AUTHOR]

Thin Mn2Ga films were grown on MgO substrates with different thicknesses of Cr buffer layer using the molecular beam epitaxy technique. The cubic half-Heusler $C1_{b}$ structure is obtained when the thickness of Cr buffer layer is below 3 nm. The phase is proven to show soft ferrimagnetism with a saturation magnetization $M_{s}$ of 280 emu/cc. Tetragonal hard ferrimagnetic Mn2Ga in $D0_{22}$ structure with high-perpendicular magnetic anisotropy is obtained when increasing the thickness of Cr buffer above 3 nm. Different phases of Mn2Ga films with various thicknesses of Cr buffer can be attributed to the tensile strain and the Cr–Mn2Ga interface condition. [ABSTRACT FROM AUTHOR]

L10-ordered MnAl thin films were epitaxially grown by sputtering technique. The substrate and annealing temperature dependences of the structural and magnetic properties of the films were systematically investigated to improve the magnetic properties and surface roughness. A low substrate temperature and subsequent post-annealing are the useful process to obtain MnAl films with both high magnetic anisotropy $K_{u}$ and small surface roughness $R_{a}$. We have successfully fabricated MnAl thin films deposited on MgO substrates and Cr90Ru10 buffer layers with the very high $K_{u}$ of 13 Merg/cm3, relatively small magnetization of 500 emu/cm3, and small $R_{a}$ of 0.34 nm by optimization of the substrate and post-annealing temperatures. The obtained MnAl films will be greatly useful to realize the high-density spin-transfer-torque magnetic random access memory. [ABSTRACT FROM AUTHOR]

In this study, we describe the deposition of Hf and Mo metal layers individually on Ta to compose new buffer layers, ie, Ta/Hf and Ta/Mo, where CoFeB/MgO stacks are deposited using magnetron sputtering. The synthesised Ta/Hf buffer has higher surface roughness, while the Ta/Mo buffer has lower surface roughness as compared with the Ta buffer. The surface roughness of the buffer appears to influence the interface of the subsequently deposited layers, resulting in rougher or smoother CoFeB/MgO interfaces. Additionally, we present a report on the magnetic properties of Ta, Ta/Hf, and Ta/Mo buffer samples. As the annealing temperature is below 200 °C, the saturation magnetisation (Ms) values for all buffer layers increase at similar rates, whereas the effective magnetic anisotropy energy ( Keff) values increase at varying rates. After annealing at 350 °C, Keff reaches its maximum value for Ta/Hf and Ta/Mo buffer layers, whereas the CoFeB/MgO interface width decreases to a minimum value. The width increases as the annealing temperature is increased over 350 °C, and Keff gradually decreases with increase in the annealing temperature. The CoFeB/MgO interface width is primarily dependent on the buffer/CoFeB interface width, which is a critical parameter to obtain high perpendicular magnetic anisotropy (PMA) and high-quality films. This work provides perspectives for understanding and controlling PMA from the viewpoint of interfacial structure. [ABSTRACT FROM AUTHOR]

Spin-transfer torque-magnetic random access memory (STT-MRAM) is one of the most prominent spintronic devices for replacing conventional electronic memory devices due to its extraordinary performance as it delivers fast operational speed, non-volatility, and a high-memory density. At advanced technology nodes, manufacturing process would invariably lead to bit on bit variation of STT-MRAM cell at wafer level. Here, we show that in a perpendicularly magnetized magnetic tunnel junction (MTJ), the in-plane demagnetizing tensor greatly influences the magnetization switching process of the free layer (FL). The geometrical asymmetricity was introduced to induce a varying in-plane demagnetizing field. This impacts the stability of the MTJ and requires a larger anisotropy to sustain an out-of-plane magnetization state. Interestingly, a faster switching of the FL comprising the MTJ is observed. This resultant rapid switching is ascribed to the nucleation of a reversal embryo at the defect. [ABSTRACT FROM PUBLISHER]

Buffer-layer dependences of dead-layer thickness, saturation magnetization ( M\mathrm {s}) , and interface magnetic anisotropy ( K\mathrm {s}) were systematically investigated for Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy ultrathin films with Pd, Ru, and Cr buffer layers. Perpendicular magnetization was only achieved in 0.6 and 0.8 nm-thick CFMS ultrathin films deposited on Pd buffer layer and annealed at 400 °C. At the optimum annealing temperature of 400 °C, K\mathrm {{s}} of 1.2 erg/cm2 was obtained for the Pd buffer layer, which was 3–6 times larger than those for Ru and Cr buffer layers. The difference in K\mathrm {{s}} probably originates from the interdiffusion and different crystallized compounds at the interface between Pd (Ru, Cr) and CFMS layers. [ABSTRACT FROM AUTHOR]

The effect of buffer layer annealing on the growth of (001)-textured 3 nm thick MnGa films with perpendicular magnetic anisotropy (PMA) was investigated. The film stacking of Si/SiO2 substrate/MgO/Cr/CoGa/MnGa was fabricated by magnetron sputtering. It was found that the CoGa buffer layer crystallized with a (001) orientation and B2 chemical ordering even without any thermal treatments. Interestingly, the 3 nm thick MnGa grown on the un-annealed CoGa buffer layer showed PMA, indicating that the CoGa buffer layer promoted the growth of (001)-textured MnGa films with L10 chemical ordering even without the annealing process. Annealing the CoGa buffer layer above 400 °C improved the (001) orientation of the CoGa buffer and MnGa layers. The effective PMA constant Ku^{\mathrm{ eff}} was about 4 Merg/cm3 without the annealing and was slightly reduced with increasing the annealing temperature, whereas the PMA dispersion was improved by the annealing. These results can help to obtain (001)-oriented MnGa ultrathin films with high PMA. [ABSTRACT FROM AUTHOR]

We report a study on the evolution of perpendicular magnetic anisotropy (PMA) in Ta/Mo/CoFeB/MgO/Ta junctions annealed at 350 °C for different periods of time. The PMA quickly developed after a short annealing time followed by a slow approach to saturation. This evolution of PMA was accompanied by structural changes. The surface roughness ( R q ) gradually increased with increasing annealing time to 30 min; further increases in annealing time resulted in a dramatic increase in R q . The effects of film composition and chemical state on magnetic anisotropy in the as-deposited Ta/Mo/CoFeB/MgO/Ta films and annealed films were studied. The X-ray photoelectron spectroscopy results demonstrated that more Fe oxides were formed at the CoFeB/MgO interface after 1 min of annealing compared to in the as-deposited sample, which is critical to obtain the PMA. High-resolution transmission electron microscopy analysis revealed that the CoFeB and MgO layers are predominantly amorphous in sample as-deposited and after 1min annealing. However, the CoFeB and MgO layers are crystallized in sample after 30 and 60 min annealing, which is beneficial to get high PMA. [ABSTRACT FROM AUTHOR]

This paper analyzes write errors in spin-torque switching due to thermal fluctuations in a system with perpendicular magnetic anisotropy. Prior analytical and numerical methods are summarized; a physics-based general 2-D Fokker–Planck equation (FPE) is solved numerically. Due to its computational efficiency and broad applicability to all switching regimes and system symmetries, the 2-D FPE has been used to study the relation between write error slope and material parameters as well as some emerging switching schemes. [ABSTRACT FROM PUBLISHER]

Magnetic tunnel junctions (MTJs) with interfacial perpendicular magnetic anisotropy (PMA) attract much attention due to their utilization in spin-transfer torque magnetic random-access memory (STT-MRAM). Large interfacial PMA provides high thermal stability, which is critical for large-capacity MTJ arrays. We investigate the thermal stability and interfacial PMA needed for STT-MRAM applications. A thermal stability factor of 75 is required for data retention time of 10 years, which implies an interfacial PMA value of 4.7 mJ/m2 as device sizes scale down to 10 nm. Even though a small retention time (e.g., 1 ms) is sufficient in some applications, such as cache memory, an interfacial PMA greater than 3.1 mJ/m2 would be necessary for 10 nm MTJ pillars. When read disturbance is taken into consideration, the PMA should be larger. These findings provide guidelines for the design of sub-20 nm MTJ devices for large-capacity STT-MRAM. [ABSTRACT FROM PUBLISHER]

We present a synthesis/processing method for fabricating ferrimagnetic insulator (Bi-doped yttrium iron garnet) thin films with tunable magnetic anisotropy. Since the desired magnetic properties rely on controllable thickness and successful doping, we pay attention to the entire synthesis/processing procedure (nanopowder synthesis, nanocrystalline target preparation and pulsed laser deposition (PLD)). Atomically flat films were deposited by PLD on (111)-orientated yttrium aluminum garnet. We show a significant enhancement of perpendicular anisotropy in the films, caused by strain-induced anisotropy. In addition, the perpendicular anisotropy is tunable by decreasing the film thickness and overwhelms the shape anisotropy at a critical thickness of 3.5 nm. IMPACT STATEMENT Strain-induced perpendicular magnetic anisotropy (PMA) in heavily Bi substituted YIG films for ferrimagnetic insulator based spintronic studies and devices. [ABSTRACT FROM AUTHOR]

The perpendicular magnetic anisotropy (PMA) and the anomalous Hall effect (AHE) in Co/Ni multilayer were optimized by manipulating its interface structure (inducing HfO 2 capping layer and Pt insertion) and post-annealing treatment. A strong PMA can be obtained in Co/Ni multilayers with HfO 2 capping layer even after annealing at 400 °C. The heavy metal Hf may improve the interfacial spin-orbit coupling, which responsible for the enhanced PMA and high annealing stability. Moreover, the multilayer containing HfO 2 capping layer also exhibited high saturation anomalous Hall resistivity through post-annealing, which is 0.85 μΩ cm after annealing at 375 °C, 211% larger than in the sample at deposited state which is only 0.27 μΩ cm. The enhancement of AHE is mainly attributed to the interface scattering through post-annealing treatment. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) have received great research attention in recent times because of their novel microstructures and properties. Among HEAs, eutectic HEA (EHEA) AlCoCrFeNi 2.1 is considered particularly attractive because of its unprecedented mechanical properties. However, the functional properties of EHEA have been hardly explored. In the present work, we have investigated the magnetic properties of nanocrystalline EHEA films grown by RF magnetron sputtering in the as-deposited and after annealing at 200 °C, 400 °C, and 600 °C in vacuum. Further, the magnetic behavior was correlated with structural and chemical characteristics. Grazing incidence X-ray diffraction (GIXRD) of the films shows the presence of FCC and BCC phases similar to the target (bulk) material. Static and dynamic magnetic properties of the HEA films are investigated by using vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques, respectively. VSM results reveal the presence of the perpendicular magnetic anisotropy (PMA) in our films annealed at 600 °C, whereas the as-deposited and samples annealed at 200 °C and 400 °C exhibit only in-plane anisotropy behavior. The presence of PMA is further supported by the FMR dynamics results. The origin of PMA in sample annealed at 600 °C is attributed to the formation of Al 2 O 3 , which has been confirmed through GIXRD and amply corroborated by X-ray photoelectron spectroscopy (XPS). The interfacial hybridization effect between Co/Fe-3d and the adjacent O-2p orbitals of Al 2 O 3 possibly resulted in PMA in HEA films. [Display omitted] • Eutectic HEA (EHEA) AlCoCrFeNi 2.1 films are grown by RF magnetron sputtering and annealed at 200 °C, 400 °C and 600 °C in vacuum. • A crossover from in-plane anisotropy to perpendicular magnetic anisotropy (PMA) is observed in vibration sample magnetometry (VSM) measurements in EHEA thin films as a function of annealing temperature. Ferromagnetic resonance (FMR) measurements further reinforced the presence of PMA in EHEA thin films. • The origin of PMA is attributed to the interfacial hybridization effect between 3d orbitals of Co/Fe and the adjacent 2p orbitals of O from Al 2 O 3, which is strongly supported by Grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS) measurements. [ABSTRACT FROM AUTHOR]

Devices with ferromagnetic layers possessing a perpendicular magnetic easy axis are of great interest due to miniaturization capability and thermal stability, retaining deeply scaled magnetic bits over long periods of time. While the tunneling magnetoresistance effect has significantly enhanced electrical reading of magnetic bits, fast and energy efficient writing of magnetic bits remains a challenge. Current-induced spin-orbit torques (SOTs) have been widely considered due to significant potential for fast and energy-efficient writing of magnetic bits. However, to deterministically switch the magnetization of a perpendicularly magnetized device using SOTs, the presence of a magnetic field is required, which offsets possible advantages and hampers applications. In this paper, a perpendicularly magnetized device is presented, which, without the need for a magnetic field, can be deterministically switched in both toggle and nontoggle modes using a damping-like SOT induced by an in-plane current pulse. This capability is realized by shaping the magnetic energy landscape. Present device does not require any materials other than those widely utilized in conventional spin-orbit devices. The device provides two orders of magnitude enhancement in switching energy-time product as compared with state-of-the-art perpendicularly magnetized devices operating on spin-transfer torques. [ABSTRACT FROM AUTHOR]

Tb x Fe 100 − x (with x =11, 25, 31 and 44) thin films were prepared with the substrates kept at a temperature of 300 °C and the Hall resistivities and electrical resistivities were investigated in the temperature range 25–300 K. The sign of Hall resistivity is found to change from positive for x =31 to negative for x =44 film at temperatures 25 K and 300 K, reflecting the compensation of Tb and Fe magnetic moments between these two compositions. Perpendicular magnetic anisotropy was observed in the films of x =25 and 31 at 25 K as well as at 300 K. The Hall resistivity is seen to increase for the films of x =11 and 31 with increasing temperature, while it decreases for the films of x =25 and 44 with increasing temperature. The temperature coefficients of electrical resistivities of these films are seen to be positive. The presence of perpendicular magnetic anisotropy (refers to magnetic anisotropy, in this paper) in the temperature range 25–300 K in Tb 25 Fe 75 and Tb 31 Fe 69 and their metallic nature are indicators that the Tb–Fe films deposited at higher temperatures are more suitable for magneto optic data storage applications than their amorphous counterparts, due to the stability of the former. [ABSTRACT FROM AUTHOR]