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A back-end-of-line compatible 400 °C thermally robust perpendicular spin-orbit torque magnetic tunnel junction (p-SOT-MTJ) memory cell with a tunnel magnetoresistance ratio of 130% is demonstrated. It features an energy-efficient spin-transfer-torque-assisted field-free spin-orbit torque (SOT) switching and a novel interface-enhanced synthetic antiferromagnet (SAF). The optimal SAF with a Ru (9 Å) spacer sandwiched by Co/Pt multilayers has a high SAF coupling field of 2.8 kOe. The parallel magnetic coupling between the CoFeB-based reference layer and the bottom Co/Pt multilayer is enhanced by a magnet-coupling face-centered cubic textured Co/Pt (5 Å) multilayer buffer. The thermally induced Pt–Fe interdiffusion is effectively reduced by the W (3 Å) trilayers of texture-decoupling diffusion multibarrier. The Ta/ $\beta $ -W and TaN/ $\beta $ -W composite SOT channels are thick enough to be the etching stop and sustain 400 °C annealing without transforming to $\alpha $ -W. Using the harmonic Hall voltage measurement, the Ta/W and TaN/W channels exhibit the large effective spin Hall angle of approximately −0.21 and −0.27, respectively. Scaling magnetic tunnel junction (MTJ) down to 30 nm size can reduce the switching time due to single-domain switching based on the micromagnetic simulation. The damping constant of ~0.018 is obtained by the ferromagnetic resonance measurement. A bigger damping constant reduces the switching time as predicted by the calibrated simulation. [ABSTRACT FROM AUTHOR]

Current induced magnetization switching is of particular interest to develop non-volatile magnetic memories (MRAM). We studied spin–orbit torque (SOT) switching in a Pt/ferromagnet/antiferromagnet Pt/[Co/Ni]2/PtMn Hall cross. For the as-deposited sample, which showed no exchange bias effect, SOT switching is observed only under an in-plane applied field. In this case, when the in-plane applied field tends to zero, the current switching required diverges and the Hall voltage signal generated by the switching tends to zero. However, the same sample is annealed perpendicular to the plane and then in an in-plane applied field, which demonstrated not only square Hall voltage vs current hysteresis loops but also a moderate switching current in zero magnetic field. This procedure induces an out-of-plane exchange bias with strengthened perpendicular magnetic anisotropy and an in-plane exchange bias, which induces zero field SOT switching. The study of the SOT switching for both annealing procedures as a function of the injected current and the in-plane field is shown. These results could impact the design of future spintronics devices such as SOT-MRAM. [ABSTRACT FROM AUTHOR]

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner–Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array. [ABSTRACT FROM AUTHOR]

The laminated soft layer (LSL) that comprises the granular [CoPtCr–SiO2/Pt]N multilayers with perpendicular magnetization is designed to reduce the switching field of exchange coupled composite (ECC) media. The magnetic simulation shows that the reduction in the switching field can be optimized by changing the coupling strength between the adjacent CoPtCr–SiO2 layers in LSL. The reversal mechanism of ECC media with LSL depends on the bilayers number N of [CoPtCr–SiO2/Pt]N. Both simulation and experiments reveal that the domain-wall assisting reversal strongly depends on the thickness of LSL. By properly adjusting the coupling strength inside the LSL, the switching and saturation fields can be significantly reduced at a limited thickness of the soft layer due to decreased domain-wall length by the Pt lamination. [ABSTRACT FROM AUTHOR]

We investigated the reorientation of exchange anisotropy in the epitaxial (002) IrMn/CoFe bilayers. Transitions of exchange-bias field from a negative field to a positive field with increasing time scale were observed at room temperature. The negatively magnetized state combining with the strong magnetocrystalline anisotropy of CoFe may raise the probability that the interfacial spins of thin IrMn layers were thermally relaxed to the direction of CoFe magnetization; therefore, after a period of time, the exchange-bias direction was reversed. This process can be further enhanced when samples were placed under the setting field. The double-shifted magnetization curve observed in this system was used as a good indicator for the relaxation of interfacial spins of IrMn. [ABSTRACT FROM AUTHOR]

The oscillatory perpendicular interlayer-coupling field and strength as a function of Ru spacer thickness were studied for samples of the [Co/Pt]5/Co/Ru/Co/TbCo structure. For Ru thickness in the range of 0.5–1 nm, a strong antiferromagnetic (AF) coupling (J∼0.38 erg/cm2) was observed. When AF coupling existed, the coercivity of Co/TbCo bilayers was enhanced because the Co/Pt multilayers stabilized the magnetization direction of Co/TbCo. Consequently, oscillatory coercivity of Co/TbCo with Ru thickness was also observed. Since the magnetization direction of the Co sublattice in TbCo can be tuned by adjusting composition or measuring temperature, the direction of the shifted minor loop of Co/Pt multilayers can be varied accordingly while keeping the same Ru thickness. [ABSTRACT FROM AUTHOR]

FeTaCN films, prepared by using reactive sputtering, were studied for the application for soft underlayers of perpendicular media. As-deposited FeTaCN nanocrystalline films with a N[SUB2]/Ar ratio of 5% exhibited high saturation moment (B[SUBs] = 1.63 T) and low coercivity (1.4 Oe). IrMn/FeTaCN exchange-biased multilayer films and CoSm/FeTaCN hard-biased films were investigated to control the domain structure and magnetization reversal in FeTaCN films. Exchange bias field is inversely proportional to the thickness of FeTaCN films and reaches 11.4 Oe in the laminated sample of [IrMn (8 mm)/FeTaCN (50 nm)]×4. The interfacial coupling energy between IrMn and FeTaCN is 0.09 erg/cm[SUP2]. The biasing field of CoSm/FeTaCN can reach a maximum value of 10.6 Oe at the FeTaCN thickness of 200 nm. The corresponding interfacial coupling energy of FeTaCN/CoSm is as large as 0.27 erg/cm[SUP2]. [ABSTRACT FROM AUTHOR]

We demonstrate a simple method to tailor the magnetization reversal mechanisms of Co/Pt multilayers by depositing them onto large area nanoporous anodized alumina (AAO) with various aspect ratios, A=pore depth/diameter. Magnetization reversal in composite (Co/Pt)/AAO films with large A is governed by strong domain-wall pinning, which gradually transforms into a rotation-dominated reversal for samples with smaller A, as investigated by a first-order reversal curve method in conjunction with analysis of the angular dependent switching fields. The change in the magnetization reversal mode is attributed to topographical changes induced by the aspect ratio of the AAO templates. [ABSTRACT FROM AUTHOR]

Exchange fields accompanying vertical magnetization shifts were observed in the epitaxial ZnCo0.07O (dilute magnetic semiconductor)/NiO system after field cooling. Transitions of exchange fields and magnetization shifts were observed at 50 K, above which the magnetization shift disappeared and the exchange field was significantly reduced. Both the exchange field and the magnetization shift increased with increasing cooling-field strength at temperatures below 50 K, which might be attributed to the existence of “frozen” spins in ZnCoO. The observed linear dependence of the exchange field on the magnetization shift may directly elucidate the role of pinned spins on the exchange fields. [ABSTRACT FROM AUTHOR]

By using first order reversal curves (FORCs), we reveal distinct magnetization reversal behavior in the CoPtCr films with different oxide additives, including Ta2O5, SiO2 and their mixtures. Increasing the ratio of Ta2O5-to-SiO2 alters the inter-grain interaction from an exchange coupling (parallel) to a dipolar-field coupling (anti-parallel). During the sputtering process, the Ta2O5 additives release extra oxygen to induce the formation of CrOx, observed from X-ray absorption spectroscopy. The reduced grain-to-grain exchange coupling strength by increasing Ta2O5 additives could be attributed to the increased volume concentration of oxides and/or the presence of the CrOx. [ABSTRACT FROM AUTHOR]

Magnetic patterning, with designed spatial profile of the desired magnetic properties, has been a rising challenge for developing magnetic devices at nanoscale. Most existing methods rely on locally modifying magnetic anisotropy energy or saturation magnetization, and thus post stringent constraints on the adaptability in diverse applications. We propose an alternative route for magnetic patterning: by manipulating the local intergranular exchange coupling to tune lateral magnetic properties. As demonstration, the grain boundary structure of Co/Pt multilayers is engineered by thermal treatment, where the stress state of the multilayers and thus the intergranular exchange coupling can be modified. With Ag passivation layers on top of the Co/Pt multilayers, we can hinder the stress relaxation and grain boundary modification. Combining the pre-patterned Ag passivation layer with thermal treatment, we can design spatial variations of the magnetic properties by tuning the intergranular exchange coupling, which diversifies the magnetic patterning process and extends its feasibility for varieties of new devices. [ABSTRACT FROM AUTHOR]

We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with magnetic anisotropy up to 3.6 × 107 erg/cm3, using atomic-scale multilayer sputtering and post annealing at 400 °C for 10 s. By fixing the Pt concentration, structure and magnetic properties are systematically tuned by the Cu addition. Increasing Cu content results in an increase in the tetragonal distortion of the L10 phase, significant changes to the film microstructure, and lowering of the saturation magnetization and anisotropy. The relatively convenient synthesis conditions, along with the tunable magnetic properties, make such materials highly desirable for future magnetic recording technologies. [ABSTRACT FROM AUTHOR]

• Spin-orbit torque (SOT) switching of the single CoTb layer is realized. • The generation of self-torque depends on the thickness of CoTb. • The switching polarity of single Co 70 Tb 30 is the same as Pt. • The switching efficiency can be varied in heavy metal/CoTb due to the interplay of SOT from heavy metal and CoTb. We investigated the spin–orbit torque (SOT) switching of the single CoTb layer with or without the heavy metals (Pt and W) in different thickness to identify the self-torque effects generated in the CoTb layer. The generation of self-torque heavily depends on the thickness of CoTb. The SOT switching was not observed for a single CoTb layer with 3 nm in thickness, suggesting self-torque may be quite weak in a very thin film. A deterministic SOT switching can be obtained for a single 9 nm CoTb layer. The amplitude of the self-torque generated in CoTb is comparable to the Co/Pt case with the same switching polarity as the Co/Pt one. When 3 nm CoTb was deposited on Pt or W underlayer, the J c is smaller in W/CoTb than that of Pt/CoTb, which can be attributable to a high spin hall angle of W and negligible self-torque of CoTb. On the other hand, when the CoTb is increased to 9 nm, the J c of W/CoTb is significantly increased and becomes higher than that of Pt/CoTb. The enhanced J c of W/CoTb may result from the opposite sign of spin orbit torque generated in W and CoTb. Since the self-torque generated in 9 nm CoTb becomes substantial, the competition of spin orbit torque between W and CoTb occurs, leading to a high J c. Our findings may shed light to utilize self-torque induced in rare earth-transition metal alloy for new design of SOT devices. [ABSTRACT FROM AUTHOR]

The magnetic circular dichroism in X-ray absorption is employed to study the element-specific magnetization in a TbFe/Co bilayer system and patterned Ni80Fe20 film. Taking advantage of the energy tunability as well as the penetration power of synchrotron radiation, the magnetization directions of Co and Fe deposited in different layers were examined as a function of Co film thickness. For patterned films, the photoemission electron microscope reveals a clear correlation between the magnetic configurations and geometries of the patterns. [Copyright &y& Elsevier]

Abstract: Using the X-ray magnetic circular dichroism, we measured the orientations of magnetic moment at exchange-coupled Co/Tb x Fe1−x bilayers. The moment associated with each element was found tilting an angle with respect to surface normal. Study of the thickness dependence on Co film shows increasing planar component for thicker film. With a fixed 15Å Co layer deposited on Tb x Fe1−x , lower Tb percentage leads to larger tilting angle. Element-specific measurements confirm that all three moments have similar orientation at interface, suggesting strong interlayer coupling. [Copyright &y& Elsevier]