This study achieved significant enhancement in creep resistance in a dilute Mg-Al-Mn-Sm alloy by forming a thermally stable eutectic network through optimizing the Al to Sm ratio. It was found that at 200°C and 50 MPa, the steady-state creep rate of the Mg-0.8Al-0.7Mn-0.9Sm alloy was 1.10 × 10−9 s−1, nearly two orders of magnitude lower than that of the Sm-free alloy, and no fracture occurred after 500 h of creep testing. With the increase in Al content to 2.5%, despite the suppression of Mg17Al12 formation, the creep resistance deteriorated to 2.75 × 10−8 s−1. Microstructural observations showed that the Mg-0.8Al-0.7Mn-0.9Sm alloy contained a homogeneous distribution of Al2Sm-rich eutectic network throughout the matrix. They effectively pinned dislocations, suppressed twin growth and coalescence as a manifestation of enhanced microstructural stability, and reduced damage accumulation along grain boundaries during creep. In contrast, even with a higher alloy concentration, the fraction of eutectic particles was much lower. Solidification simulations revealed that a low Al/Sm ratio led to a wide Al2Sm formation window of approximately 84°C and a final eutectic fraction of 7.5%, whereas a high Al/Sm ratio narrowed the window to approximately 20°C and produced only discrete Al-Sm compounds with a final eutectic fraction of only 1.3%. Consequently, the effective creep driving force in the Mg-0.8Al-0.7Mn-0.9Sm alloy is only about 2% of that in the Mg-2.5Al-0.8Mn-0.9Sm alloy, leading to a much lower creep deformation.

The simultaneous improvement of strength and ductility was achieved in Al-Mg 5183 alloy by dilute alloying of Sc, Zr, and Ti. Compared with the non-microalloyed 5183 alloy (benchmark), the yield strength and elongation increased simultaneously from 178 MPa to 212 MPa and from 27% to 34%, respectively. The microalloying addition significantly refined grain size. With solid solution of Zr and Ti in Al3Sc, the lattice mismatch between the L12Al3(ScZrTi) nanoparticles and Al matrix was only ~0.2%, resulting in effective grain refinement. In-situ characterization results showed uniform deformation in the 5183-(ScZrTi) alloy matrix throughout tensile test, but cracking in the Al3(ScZrTi) and Mg2Si primary compounds at large strain, which was identified as the origin of fracture. In contrast, the 5183 benchmark failed after macroscopic necking, accompanied by edge cracking in the gauge section, even at much lower strain. The crystal plasticity modelling showed that, regardless of grain size, localized strain was prone to develop at the grain boundary segments, which were ~45 degrees to the tensile direction. With microalloying, a high density of such grain boundaries provided numerous sites for micro shear band formation. They were then connected and widened, eventually becoming diffuse strain zones among neighboring grains during further deformation. Without microalloying, coarse grains provided fewer sites for micro shear band formation. The sparsely distributed shear band developed sharp strain localization, rather than diffuse strain zones, which was associated with earlier necking and edge cracking. This study provides new insight into better ductility at higher strength through shear band-mediated plasticity.

The age-hardening response and related precipitate microstructure in Mg–Pb alloys with different Zn contents have been examined systematically. The age-hardening response significantly improves with increasing Zn content. Specifically, the addition of 3 wt

While compositional gradient-induced spin-current generation is explored, its microscopic mechanisms remain poorly understood. Here, the contribution of polarity of compositional gradient on spin-current generation is explored. A nanoscale compositional gradient, formed by in situ atomic diffusion of ultrathin Ti and W layers, is introduced between 10-nm-thick W and Ti layers. Spin-torque ferromagnetic resonance in ferromagnetic Ni95Cu5 deposited on this gradient reveals that a moderate compositional gradient suppresses negative spin torque from the spin Hall effect in W. In contrast, reversing the Ti/W stacking order, which inverts the gradient, suppresses positive spin torque from the orbital Hall effect in Ti. These findings suggest that the sign of spin torque is governed by the polarity of compositional gradient, providing a novel strategy for efficient spin-torque generation without relying on materials with strong spin or orbital Hall effect.

Green materials for efficient charge-to-spin conversion are desired for common spintronic applications. Recent studies have documented the efficient generation of spin torque using spin-orbit interactions (SOIs); however, SOI use relies on the employment of rare metals such as platinum. Here, we demonstrate that a nanometer-thick gradient from silicon to aluminum, which consists of readily available elements from earth resources, can produce a spin torque as large as that of platinum despite the weak SOI of these compositions. The spin torque efficiency can be improved by decreasing the thickness of the gradient, while a sharp interface was not found to increase the spin torque. Moreover, the electric conductivity of the gradient material can be up to twice as large as that of platinum, which provides a way to reduce Joule heating losses in spintronic devices.

Altermagnetism presents intriguing possibilities for spintronic devices due to its unique combination of strong spin-splitting and zero net magnetization. However, realizing its full potential hinges on fabricating single-variant altermagnetic thin films. In this work, we present definitive evidence for formation of single-variant altermagnetic RuO2(101) thin films with fully epitaxial growth on Al2O3(1 1 ¯ 02) r-plane substrates, confirmed through rigorous structural analyses using X-ray diffraction, atomic-resolution transmission electron microscopy and X-ray magnetic linear dichroism. The mutual correspondence of the occupancy of oxygen atoms on the surfaces of RuO2(101)[010] and Al2O3(1 1 ¯ 02)[11 2 ¯ 0] plays a decisive role in the formation of the single-variant RuO2, which is also supported by our first-principles density functional theory calculations. We further observed spin-splitting magnetoresistance in the single-variant RuO2(101)/CoFeB bilayers, highlighting the characteristic effect of single variant on spin transport. The demonstration of single-variant RuO2(101) films marks a significant advancement in the field of altermagnetism and paves the way for exploring their potential applications.

We present a novel method for generating spin currents using the gyromagnetic effect, a phenomenon discovered over a century ago. This effect, crucial for understanding the origins of magnetism, enables the coupling between various macroscopic rotational motions and electron spins. While higher rotational speeds intensify the effect, conventional mechanical rotations, typically below 10,000 RPM, produce negligible results comparable to geomagnetic fluctuations, limiting applied research. Our studies demonstrate that spin current generation comparable to that of rare metals can be achieved through atomic rotations induced by GHz-range surface acoustic waves and the rotational motion of conduction electrons in metallic thin films with nanoscale gradient modulation of electrical conductivity. These effects, termed the acoustic gyromagnetic effect and the current-vorticity gyromagnetic effect, are significant in different contexts. The acoustic gyromagnetic effect is notable in high conductivity materials like aluminum and copper, which are more abundant than conventional spintronics materials with strong spin-orbit interactions (SOIs). Conversely, the current-vorticity gyromagnetic effect requires a large conductivity gradient to produce current vorticity efficiently. This is achieved by using composition gradient structures from highly conductive metals to poorly conductive oxides or semiconductors. Consequently, unlike traditional strong-SOI materials, we can create highly efficient spin current generators with low energy dissipation due to reduced Joule loss.

Stacking faults (SFs) and the interaction between solute atoms and SFs in a Mg–Bi alloy are investigated using aberration-corrected scanning transmission electron microscopy. It is found that abundant I1 SFs are generated after cold rolling and are mainly distributed inside {101¯2} twins. After aging treatment, the formation of single-layer and three-layer Bi atom segregation in the vicinity of I1 fault are clearly observed. Bi segregation also occurs at the 1/6<22¯03> bounding Frank partial dislocation cores. The segregation behaviors in I1 fault and Frank dislocations are discussed and rationalized using first-principles calculations.

The cubic perovskite SrMoO3 with a paramagnetic ground state and remarkably low room-temperature resistivity has been considered as a suitable candidate for the new-era oxide-based technology. However, the difficulty of preparing single-phase SrMoO3 thin films by hydrogen-free sputtering has hindered their practical use, especially due to the formation of thermodynamically favorable SrMoO4 impurity. In this work, we developed a radio frequency sputtering technology enabling the reduction reaction and achieved conductive epitaxial SrMoO3 films with pure phase from a SrMoO4 target in a hydrogen-free, pure argon environment. We demonstrated the significance of controlling the target-to-substrate distance (TSD) on the synthesis of SrMoO3; the film resistivity drastically changes from 1.46 × 105 μΩ·cm to 250 μΩ·cm by adjusting the TSD. Cross-sectional microstructural analyses demonstrated that films with the lowest resistivity, deposited for TSD = 2.5 cm, possess a single-phase SrMoO3 with an epitaxial perovskite structure. The formation mechanism of the conductive single-phase SrMoO3 films can be attributed to the plasma-assisted growth process by tuning the TSD. Temperature-dependent resistivity and Hall effect studies revealed metal-like conducting properties for low-resistive SrMoO3 films, while the high-resistive ones displayed semiconductor-like behavior. Our approach makes hydrogen-free, reliable and cost-efficient scalable deposition of SrMoO3 films possible, which may open up promising prospects for a wide range of future applications of oxide materials.

Epitaxial thin films of fully nonequilibrium hcp-Ru50Mo50(0001) nanoalloys were prepared as a chemically disordered alloy, in which the intrinsic spin Hall effect is expected to be negligible. Structural analyses confirmed the epitaxial growth and atomic scale alloying of the films. In contrast to a tiny torque efficiency (ξDL) of ∼0.4% for Ru50Mo50/CoFeB, the ξDL for the Ru50Mo50/Ni heterostructure reached ∼30% with a long-range relaxation length. The apparent dependence of ξDL on the ferromagnetic layer can be attributed to the orbital Hall effect (OHE). Interestingly, a smaller ξDL was observed for Ru/Ni, suggesting that the nonequilibrium Ru50Mo50 enhances its OHE. Furthermore, the enhanced ξDL is maintained by inserting a Ru layer between the Ru50Mo50 and Ni layers, showing orbital transport through Ru. This finding illustrates potential applications of nonequilibrium nanoalloy films in spin orbitronics and contributes to getting insights into the understanding of the interrelationships between nanostructures and orbital transport properties.

We report the structural feature of sputter-deposited epitaxial [Co (0.2 nm)/Pt (0.2–1.0 nm)] multilayered films prepared with various periodic structural designs consisting of non-integer numbers of Co and Pt monoatomic layers on an atomically flat Ru(0001). Sharp superlattice modulation peaks and their systematic changes with the Pt thicknesses were observed in the x-ray diffraction (XRD) spectrum. The formation of periodic structures shows that layer-by-layer like growth occurs and the resulting incommensurate superlattice modulation survives down to an atomic scale even in the sputter-deposited Co/Pt multilayers. Magnetic properties were also investigated for the Co/Pt multilayers. Interestingly, the maximum perpendicular magnetic anisotropy Ku of 3 × 106 erg/cm3 was obtained for the [Co (0.2 nm)/Pt (0.3 nm)] multilayer exhibiting incommensurate superlattice modulation peaks, while the [Co (0.2 nm)/Pt (0.2 nm)] multilayer with a L11-like XRD peak showed a smaller Ku. A cross-sectional high-angle annular dark-field scanning transmission electron microscopy analysis revealed that a partially L11-ordered CoPt structure is formed in the [Co 0.2 nm/Pt 0.2 nm] multilayer, interpreting the observed Ku. This study gives a new insight into the structural feature of sputter-deposited Co/Pt multilayers useful for a wide range of spintronic devices, such as magnetic tunnel junctions.

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic Ni95Cu5 alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

Significant spin current generation from highly conductive materials is promising for spintronic applications, such as spin-orbit-torque magnetic random-access memories. In this work, we fabricated epitaxial Ru/Cu heterostructures with interface engineering where 1-nm-thick Ru and Cu layers were alternately deposited at the interface. The spin current generation in the heterostructures was evaluated by unidirectional spin Hall magnetoresistance and spin-torque ferromagnetic resonance. A sizable spin Hall efficiency (~−2%) was achieved in the Ru/Cu sample with a sharp interface which may result from the interface spin filtering effect. Increased spin Hall efficiency (~−4%) was observed in the interface-engineered samples which could be attributed to the intrinsic contribution from lattice distortion and local band structure near the interface. The effective spin Hall conductivity was estimated to be $3\sim 5 \times {10^5}\frac{{h}}{{2e}}{\Omega ^{ - 1}}{{\text{m}}^{ - 1}}$, which is comparable to that of Platinum.

Magnetic tunnel junctions (MTJs) with bcc(001)-type structures such as Fe(001)/MgO(001)/Fe(001), have been widely used as the core of various spintronic devices such as magnetoresistive memories; however, the limited material selection of (001)-type MTJs hinders the further development of spintronic devices. Here, as an alternative to the (001)-type MTJs, an fcc(111)-type MTJ using a fully epitaxial CoFe/rock-salt MgAlO (MAO)/CoFe is explored to introduce close-packed lattice systems into MTJs. Using an atomically flat Ru(0001) epitaxial buffer layer, fcc(111) epitaxial growth of the CoFe/MAO/CoFe trilayer is achieved. Sharp CoFe(111)/MAO(111) interfaces are confirmed due to the introduction of periodic dislocations by forming a 5:6 in-plane lattice matching structure. The fabricated (111) MTJ exhibits a tunnel magnetoresistance ratio of 37% at room temperature (47% at 10 K). Symmetric differential conductance curves with respect to bias polarity are observed, indicating the achievement of nearly identical upper and lower MAO interface qualities. Despite the charge-uncompensated (111) orientation for a rock-salt-like MAO barrier, the achievement of flat, stable, and spin-polarized barrier interfaces opens a promising avenue for expanding the design of MTJ structures.

The demonstration of the charge-to-spin conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin–orbit torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1 nm)/Ru (1 nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency ( ξ DL ) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeable ξ DL of −2.2% and the insertion of Cu/Ru nanolayers at the interface can increase the ξ DL value to −3.7%. The former could be attributed to the interface spin–orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3∼5) × 10 5 ℏ 2 e Ω −1 m −1 in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin–orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

Nano-crystal domain structures formed in a MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) have been systematically studied using scanning transmission electron microscopy and first-principles calculations. These domains are widely distributed in the (111)-textured MgO layer, being different from conventional bcc-CoFe/MgO(001)-based MTJs. The (111)-texture is formed by extension of {111} planes through several adjacent MgO domains. Three types of orientation relationships (ORs) between CoFe and MgO are identified, including cube-on-cube type (Type-1), twin-like type (Type-2), and unexpected type (Type-3). Crystallographic analysis indicated that Type-2 OR is a variant of Type-1 OR, triggered by different stacking orders of MgO(111) planes, while Type-3 OR is formed by a 30° in-plane rotation of MgO lattice relative to Type-1 OR. Due to the large in-plane lattice mismatch (19.6%) between Co(111) and MgO(111) in Type-1 and Type-2 ORs, Type-3 OR (mismatch 3.4%) can be stabilized. First-principles calculations uncovered that the theoretical TMR ratio of the MgO(111) MTJ with Type-3 OR is ∼2 orders of magnitude smaller than that with Type-1 and Type-2 ORs. The small contribution of Type-3 OR to the transport reasonably interprets why the experimental TMR ratio (∼37%) is much lower than the theoretical value (∼2100%) in the Co/MgO/Co(111) MTJ. This study has revealed the nano-crystal domain formation unique to the fcc-CoFe/MgO(111) MTJs, indicating that controlling the nano-crystal domains (e.g., lattice optimization by atomic doping) can be a guiding principle to develop MgO(111)-based epitaxial MTJs and related heterostructure devices.

This study demonstrates the yield asymmetry in Mg-3Al-1Zn alloy containing both ND-texture (c-axis // ND (Normal direction)) and TD-texture (c-axis // TD (Transverse direction)) in a quantitative view. The results showed that the yield asymmetry is strongly dependent on the distribution of bimodal texture components, on the basis of the successful establishment of the quantified relationship between pre-deformation parameters and texture components distribution. It's meaningful for providing key reference to texture design. Mechanical behavior of bimodal textured Mg alloy under tension and compression was tested. CYS/TYS (compressive yield stress / tensile yield stress) equal to 1 is obtained, implying that the yield asymmetry is eliminated when two textures distribute at specific fractions. The corresponding mechanism for the texture-dependence of tension-compression yield asymmetry is revealed by the analysis of slip/twinning activities and a compound use of the activation stress difference of slip/twinning (delta Stress) and geometrical compatibility factor (m') between neighboring grains. Balanced activity of {1012} twinning and a quite similar boundary obstacle effect against slip/twinning transfer under tension and compression accounts for such good symmetry performance. (C) 2022 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.

Mixed failure of rock by tension and shear occurs frequently in underground openings, rock slopes, and trans -tension faults. In this study, a simple auxiliary device (which consists of an indenter and a hollowed base) is proposed to implement tension-shear tests of rock samples combined with a servo-controlled uniaxial compression machine. Experimental and numerical tension-shear tests are carried out on red sandstones using the proposed auxiliary device and particle flow code. The effects of sample height H and base hollow diameter D on the mechanical behaviors are analyzed in detail, including the peak load, fracture characteristics, and AE characteristics. The results show that peak load increases with the sample height while decreases with hollow diameter due to the change of inclination angle of the failure surface. The initial crack and dominant cracks changed from shear cracks to tensile cracks as D increase from 2 cm to 4 cm, which suggests the transition from shear failure to hybrid tension-shear failure.

Deformation twins in Mg–Gd alloys are investigated. It is found that the dominant twinning mode switches from {101¯2} twinning to {112¯1} twinning, with an increase in the Gd concentration in Mg. Our first-principles calculations suggest that the formation of the {112¯1} twin in the Gd-rich alloy is triggered by the reduced {112¯1} twin boundary energy, which results from strain relaxation along the twin boundary. Furthermore, this twinning mode is suggestive to be activated in other Mg alloys with a high concentration of solute atoms having larger size than Mg.

Deformation twins in Mg-Gd alloys are investigated. It is found that the dominant twinning mode switches from {10 (1) over bar2} twinning to {11 (2) over bar1} twinning, with an increase in the Gd concentration in Mg. Our first-principles calculations suggest that the formation of the {11 (2) over bar1} twin in the Gd-rich alloy is triggered by the reduced {11 (2) over bar1} twin boundary energy, which results from strain relaxation along the twin boundary. Furthermore, this twinning mode is suggestive to be activated in other Mg alloys with a high concentration of solute atoms having larger size than Mg. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.