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Field-free spin–orbit torque switching in synthetic antiferromagnets (SAF) holds significant promise for high-density spintronic memory and logic devices. In this paper, we realize the field-free magnetization switching in SAFs due to the local ion implantation-induced 45° lateral interface and symmetry breaking. Moreover, the magnetization switching ratio is enlarged by the lateral interface owing to the superimposition of a damping-like effective field and a symmetry-breaking effective field. Our work is significant for the development of magnetic random-access memory technology with high-speed and anti-interference ability. [ABSTRACT FROM AUTHOR]

By means of local ion implantation, we investigated the influence of lateral interface on current induced magnetic switching by spin–orbit torque in a perpendicularly magnetized Pt/Co/Ta multilayer. The experimental results show that, in this system, the domain wall motion under electrical current can be affected by two mechanisms: symmetry breaking and current-driven Néel wall motion at the lateral interface. The dominant mechanism is symmetry breaking (current-driven Néel wall motion) at the large (small) current. Due to the competitive relationship of these two mechanisms, the non-hysteresis effect magnetic switching without an external magnetic field is obtained. Based on the non-hysteresis effect magnetic switching, we can realize AND and OR logic gates without resetting. [ABSTRACT FROM AUTHOR]

We proposed a multilayer structure to reduce the critical spin current density of perpendicularly magnetized layers switched by spin–orbit torque (SOT) from the spin Hall effect. In the structure, we introduced exchange-coupled perpendicularly magnetized layers composed of soft and hard magnetic layers in lieu of a single magnetic layer. The switching loops and dynamic processes under periodic spin currents have been studied by micromagnetic simulation. We have found that the critical spin current density can be substantially reduced when the saturation magnetization of the soft layer is sufficiently low. Moreover, the critical spin current density is quite insensitive to the change of exchange interaction between the two magnetic layers, which enables the multilayer structure to tolerate the variation of material composition or structure imperfections during fabrication. The introduction of exchange-coupled layers provides a way to design and optimize the SOT-driven devices and paves the path for their applications. [ABSTRACT FROM AUTHOR]

The non-collinear antiferromagnetic Weyl semimetal Mn3X (X = Ga, Ge, Sn) system has attracted a lot of attentions owing to its robust anomalous Hall effect (AHE), large spin Hall angle and small net magnetization at room temperature. The high spin-charge interconversion efficiency makes it a super candidate in topological antiferromagnetic spintronic devices, which could facilitate ultra-fast operation of high-density devices with low energy consumption. In this work, we have realized to obtain different chiral spin structures in Heusler alloy Mn3Ge thin films, which originate from different crystalline orientations. The high-quality (0002)- and (20 2 ¯ 0)-oriented single phase hexagonal Mn3Ge films are achieved by controllable growth, annealing process and ion implantation. The various magnetic properties and AHE behaviors are observed along a and c crystal axes, equivalent to magnetic field in and out of the inverse triangular spin plane. The observation demonstrates the manipulation of crystal structure accompanied with chiral spin order in a non-collinear antiferromagnetic Mn3Ge film, which is induced by energy conversion and defect introduction. The in situ thermal treatment induces crystal phase rotation up to 90° and robust AHE modulation, which is significantly important and highly desirable for flexible spin memory device applications. [ABSTRACT FROM AUTHOR]

Partially ordered Fe-N thin films were grown by a facing target sputtering process on the surface of a (001) Ag underlayer on MgO substrates. It was confirmed by x-ray diffraction that the Ag layer enlarged the in-plane lattice of the Fe-N thin films. Domains of the ordered α″-Fe16N2 phase within an epitaxial (001) α′-FexN phase were identified by electron diffraction and high-resolution aberration-corrected scanning transmission electron microscopy (STEM) methods. STEM dark-field and bright-field images showed the fully ordered structure of the α″-Fe16N2 at the atomic column level. High saturation magnetization(Ms) of 1890 emu/cc was obtained for α″-Fe16N2 on the Ag underlayer, while only 1500 emu/cc was measured for Fe-N on the Fe underlayer. The results are likely due to a tensile strain induced in the α″-Fe16N2 phase by the Ag structure at the interface. [ABSTRACT FROM AUTHOR]

Abstract: Fe (001) thin films with different crystal lattice were epitaxially grown on single crystal MgO substrates under the various sputtering pressures. It is found in this paper that the tetragonality and magnetic anisotropy of Fe thin film is tuned by varying the working sputtering pressures. The tunability of the crystal lattice and the magnetic anisotropy of Fe films were characterized by X-ray reflectivity, X-ray diffraction and vibrating sample magnetometer. The tunable structure and magnetic properties of Fe thin films may attribute to the rearrangement of Fe atoms on MgO substrate induced by controlling the atomic kinetic energy under different sputtering pressure. [Copyright &y& Elsevier]

Current-induced fast-ordering method (CIFOM) was designed to achieve an ordered L10-FePt film with small grain size under low energy consumption by applying direct current (DC) in the FePt film. The grain size (\sim 8 nm) of the L10-FePt film prepared by CIFOM method is about one-third of that produced by the post-annealing method (PAM). The fast ordering of the L10-FePt film by CIFOM is probably attributed to the momentum exchange between the FePt atoms and the conductive electrons. The short ordering time by CIFOM contributes to the smaller grain size of FePt film. [ABSTRACT FROM AUTHOR]

• A new method to estimate the spin Hall angle and anisotropy field has been proposed. • Spin Hall angles estimated by our method are closed to that obtained using other different methods. • Estimating spin Hall angle by our macrospin model can be widely applicable for different kinds of materials. We developed equations to estimate the spin Hall angle and anisotropy field of ferromagnets in heavy metal/ferromagnet heterostructures using a macrospin model. In this model, critical switching spin current density linearly changes with the applied in-plane magnetic field. Thus the spin Hall angles can be estimated by measuring the critical switching current density under in-plane magnetic field. The obtained spin Hall angle using this method is not only consistent with that obtained by harmonic measurements. Spin Hall angles of PtMn, β-W, Pt and (Bi 0.5 Sb 0.5) 2 Te 3 estimated by our method are also closed to that obtained using other different methods. Therefore, estimating spin Hall angle by macrospin model can be considered a simple, feasible and widely-applicable approach to obtain the spin Hall angle. [ABSTRACT FROM AUTHOR]

• A field-free magnetic switching method compatible with magnetic tunneling junction. • Gradient spin current induces deterministic switching of PMA magnets. • In-plane effective field by the SOT linearly depends on gradient spin current. We investigated the current-induced magnetization switching in a perpendicular magnetized Pt/CoNiCo/Pt sandwich structure by spin-orbit torques under in-plane gradient current density. The gradient spin current density resulted from the spin Hall effect along the current direction was achieved by designing a bottom wedged Pt electrode. An in-plane effective field along the current direction is induced by the wedged Pt layer, which determines the direction of the current induced magnetization switching. The effective field increased with the slope of the wedged Pt, and is sufficient to induce deterministic switching of nearly 90% domains with the slope value of 0.21. [ABSTRACT FROM AUTHOR]

Realization of sub‐10 nm spin‐based logic and memory devices relies on the development of magnetic materials with perpendicular magnetic anisotropy that can provide low switching current and large thermal stability simultaneously. In this work, the authors report on one promising candidate, Fe16N2, a heavy‐metal‐free, non‐interface perpendicular magnetic material and demonstrate a perpendicularly magnetized current‐perpendicular‐to‐plane (CPP) giant magnetoresistance (GMR) device based on Fe16N2. The crystalline‐based perpendicular anisotropy of Fe16N2 in the CPP GMR device is measured to be about 1.9 × 106 J m−3 (1.9 × 107 erg cm−3), which is sufficient to maintain the thermal stability of sub‐10 nm devices. A first principle calculation is performed to support this large magnitude of the perpendicular anisotropy. Moreover, the Gilbert damping constant of the Fe16N2 thin film (α ≈0.01) measured by ferromagnetic resonance (FMR) is lower than for most existing materials with crystalline perpendicular magnetic anisotropy. The non‐interface perpendicular anisotropy and low damping properties of Fe16N2 may offer a pathway for future spintronics logic and memory devices. [ABSTRACT FROM AUTHOR]

• We investigate the heavy ions irradiation effect on the spin transfer torque film stacks with perpendicular magnetic anisotropy. • The results exhibit that magnetic properties of the synthetic antiferromagnet layer and the ferromagnetic exchange coupling between reference layer and synthetic antiferromagnet layer have changed significantly. • We analysis the irradiation damage by SRIM simulation and give a reasonable explanation for this phenomenon. • Our work demonstrates that perpendicular spin transfer torque MRAM technology itself, the memory element construction, is subject to damage from heavy ions irradiation. We investigate the heavy ions irradiation effect on the spin transfer torque film stacks with perpendicular magnetic anisotropy. Samples are exposed to 175 MeV Cl ion and 235 MeV Ge ion at the fluence of 1x105 ions/cm2 and 1x106 ions/cm2. Measurements of magnetization vs. magnetic field are performed on the film stacks before and after irradiation. The results exhibit that magnetic properties of free layer (CoFeB) in the spin transfer torque film keeps unchanged while magnetic properties of the synthetic antiferromagnet layer (Co/Pt) and the ferromagnetic exchange coupling between reference layer (CoFeB) and synthetic antiferromagnet layer through W layer have changed significantly when the fluence of the two kinds of ions reach 1x106 ions/cm2. We analysis the irradiation damage of the film stacks by SRIM simulation and give a reasonable explanation for this phenomenon. Thus, our work demonstrates that perpendicular spin transfer torque MRAM technology itself, the memory element construction, is subject to damage from heavy ions irradiation. [ABSTRACT FROM AUTHOR]

• Total ionizing dose effect on the voltage-controlled magnetic anisotropy Hall bar device based on HfZrO/CoFeB hybrid film. • Voltage-controlled magnetic anisotropy effect is enhanced with the accumulation of irradiation dosage. • The proposed mechanism focus on interfacial trapped charges. • HfZrO/CoFeB hybrid film possess potential for radiation-hard memory. We investigate the total ionizing dose (TID) effect on the voltage-controlled magnetic anisotropy (VCMA) Hall bar device based on HfZrO/CoFeB hybrid film. Devices under test are exposed to 1.17 MeV 60Co γ-ray at the dose rate of 50 rad(Si)/s. The Anomalous Hall measurement is performed at several certain irradiation dosages. The results show that the VCMA effect is enhanced with the accumulation of irradiation dosage. We propose a mechanism of interface trapped charges to explain this phenomenon. Thus, our work indicates that the magnetic tunneling junction based on HfZrO/CoFeB hybrid film is a promising building block for radiation-hard VCMA-MRAM (magneto-resistive random-access memory). [ABSTRACT FROM AUTHOR]

FeN alloy film is a promising spintronic material with the theoretically ultra-strong magnetism (saturation magnetization M S and magnetic anisotropy K eff ) and high spin polarization, which relies on the degree of N ordering interstice occupancy ( S ). However, due to the high activation energy for N ordering, the S value of an actual FeN film is mostly lower than 35% and this restricts the achievable magnetism and transportation property. Thus, the construction of a FeN alloy film with well-controlled magnetism and efficient electronic transportation remains a long-standing challenge. Here, we tackle the problem by strain engineering. Using an Fe/Cr underlayer, we introduced a considerable epitaxial strain in the FeN lattice. The strain is proven to effectively promote the S value to over 60%, resulting in remarkable enhancement of M S value from 2.18T to 2.81T (30% increment) and effective tunability of K eff value ranging 1.3∼2.2 × 10 6 J/m 3 . Besides, the matched energy band symmetry (Δ5) between Cr and Fe 16 N 2 facilitates the efficient electronic transportation for spintronic applications. By simulating interstice distribution with the first-principles calculations, the lattice strain is found to decrease the activation energy for N interstitial migration, which serves as a thermodynamic driving force for the magnetism tunability. [ABSTRACT FROM AUTHOR]

We report that the magnetic and electronic transport properties in oxide/NiFe(2 nm)/oxide film (oxide = SiO 2 , MgO or HfO 2 ) are strongly influenced by the electronic structure of NiFe/oxide interface. Magnetic measurements show that there exist magnetic dead layers in the SiO 2 sandwiched film and MgO sandwiched film, whereas there is no magnetic dead layer in the HfO 2 sandwiched film. Furthermore, in the ultrathin SiO 2 sandwiched film no magnetoresistance (MR) is detected, while in the ultrathin MgO sandwiched film and HfO 2 sandwiched film the MR ratios reach 0.35% and 0.88%, respectively. The investigation by X-ray photoelectron spectroscopy reveals that the distinct interfacial redox reactions, which are dependent on the oxide layers, lead to the variation of magnetic and transport properties in different oxide/NiFe/oxide heterostructures. [ABSTRACT FROM AUTHOR]

• W/Ta multilayers (1:0.25) presents a high spin Hall angle (θ SH , 2nd) and the relatively low resistivity simultaneously. • The spin Hall angle (θ SH, J c) obtained by the critical current density is measured to explore the influence from the spin Hall angle on the magnetization switching. • θ SH, J c has strong correlation with θ SH , 2nd in large dimension sample, whereas pinning effect and domain wall surface tension plays important role in θ SH, J c at the small dimension. We obtain varying spin Hall angle (θ SH, 2nd) values measured by the 2nd harmonic methods in W/Ta multilayers system with relatively low resistivity by doping Ta into mixed-phase W with both α and β phases (α- W , β- W). A remarkably increased value of θ SH, 2nd is observed from 0.04 (W) to 0.47 (W 1 /Ta 0.25), which is attributed to the formation of β -W 3 Ta. The influences of θ SH, 2nd on the critical switching current density (J c) were investigated by the spin Hall angle (θ SH, J c). It is found that the θ SH, J c has strong correlations with θ SH, 2nd in large dimension samples, indicating the J c can be lowered by the enhancement of θ SH, 2nd. This correlation gradually disappears in smaller dimension samples, due to the pinning effect and domain wall (DW) surface tension, which are confirmed by microsimulations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Study diffusion behaviors of surfactant Bi atoms in FePt spintronic films under different annealing treatments. [•] Reveal microstructure evolutions in FePt layers resulted from the Bi atomic diffusion. [•] Report the enhancements of atomic ordering transition and hard magnet property of FePt films by the Bi diffusion. [•] Explored the mechanism for magnetic property tunability in the FePt film. [•] The findings help for understanding surfactant diffusion effects in spintronic materials and designing functional spintronics devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Prepared a perpendicular ECC film with low interparticle exchange coupling. [•] Explored the magnetic property tunability in the perpendicular ECC film. [•] Studied magnetization reversal mechanism in the films. [•] The findings will help for improving S/N ratio and writability of recording media. [ABSTRACT FROM AUTHOR]

A correction to the article "'Electromigration induced fast L10 ordering phase transition in perpendicular FePt films," by Chun Feng and colleagues in a 2013 issue is presented.

Realizing fast L10 ordering phase transition (LOPT) in L10 structured magnetic materials without heat treatment is crucial for their applications in spintronic devices. This article reports on the electromigration controlled momentum transfer and rapid ordering of Fe and Pt atoms in the as-deposited FePt films. Lattice defects in the films provide enough diffusion pathways and allow the Fe and Pt atoms rearranging. Through the current driven atomic motion and rearrangement, fast LOPT can result in the establishment of perpendicular magnetic anisotropy of the FePt films at room temperature. This effect is expected to work with other L10 typed magnetic materials for spintronic devices development. [ABSTRACT FROM AUTHOR]

Based on interfacial microstructure control of FePt/Au multilayer structure and surfactant Bi atoms, an FePtBi/Au nanocomposite film was designed to achieve good properties [low-temperature ordering, good perpendicular magnetic anisotropy (PMA), and no interparticle exchange coupling (IEC)] in this paper. The ordering process was promoted due to the increase of concentration of defects by adding appropriate surfactant Bi atoms. Thus, the ordering temperature of this film can be decreased from 500 to 450 °C. Meantime, the FePtBi/Au nanocomposite film maintains good PMA and low IEC with the texture manipulation of Au layers and control of total film thickness. [ABSTRACT FROM AUTHOR]

• The Thermal stability of both SAF and reference layer change inversely when varying the thickness of tungsten bridge layer, • Thicker tungsten bridge layer induces the decoupling of SAF and reference. • Increasing tungsten bridge layer can indirectly damage the anisotropy of free layer. • The damage generated by bridge layer depends on the orange-peeling coupling of MgO. We investigated the thermal stability of spin-orbit torque magnetic tunnel junction (SOT-MTJ) thin films by tuning multiple interlayer couplings among synthetic anti-ferromagnetic layer (SAF), reference layer and free layer. We find that the bridge layer (here we use W) can influence the thermal stability of perpendicular magnetic anisotropy (PMA) in all the magnetic layers through the interlayer couplings. Increasing the thickness of bridge layer decouples the SAF and reference layer, resulting in higher PMA of SAF layer and lower PMA of reference layer. The reference layer further adjusts the PMA of free layer by orange-peel coupling via the tunneling barrier layer MgO such that we find another way to optimize the anisotropy without changing ferromagnetic layers. This work is helpful for engineering the interlayer coupling of SOT-MTJ thin films to achieve SOT devices with high thermal stability. [ABSTRACT FROM AUTHOR]