Metallic Spin Research Articles

Research on Preparation Method and Mechanism of Cylinder Ultra-fine Crystal Metal Spinning

Modern industry requires metal materials with high forming quality and excellent mechanical properties. Ultra-fine grain metal makes ordinary steel obtain good comprehensive performance, reduce the consumption of high-performance metal, improve material utilization and performance, and is of great significance to the manufacturing industry. In this paper, the body-shaped cubic metal 20# steel cylinder parts are taken as research objects. By exploring the forming principle of ultra-fine crystal structure cylindrical parts, the finite element simulation of the strong spinning process of the cylindrical parts is carried out. And the forming process experiment of ultra-fine grain structure spinning and heat treatment experiment are also carried out. Thus, the plastic deformation mechanism is revealed, and a method for preparing an ultra-fine grain material based on combination of strong spinning and recrystallization annealing is proposed. The research reveals the relationship between mechanical properties and microstructure of ultra-fine grained materials. The research results have great scientific significance for promoting the development of ultra-fine grain metal material preparation technology.

Electrical detection of the surface spin polarization of the candidate topological Kondo insulator SmB6

The Kondo insulator compound $\mathrm{Sm}{\mathrm{B}}_{6}$ has emerged as a strong candidate for the realization of a topologically nontrivial state in a strongly correlated system, a topological Kondo insulator, which can be a novel platform for investigating the interplay between nontrivial topology and emergent correlation-driven phenomena in solid-state systems. Electronic transport measurements on this material, however, so far showed only the robust surface-dominated charge conduction at low temperatures, lacking evidence of its connection to the topological nature by showing, for example, spin polarization due to spin-momentum locking. Here, we find evidence for surface-state spin polarization by electrical detection of a current-induced spin chemical-potential difference on the surface of a $\mathrm{Sm}{\mathrm{B}}_{6}$ single crystal. We clearly observe that a surface-dominated spin voltage, which is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current and is strongly temperature dependent due to the crossover from surface to bulk conduction. We estimate the lower bound of the surface-state net spin polarization as 25% based on the quantum transport model, providing direct evidence that $\mathrm{Sm}{\mathrm{B}}_{6}$ supports metallic spin helical surface states.

Cross-shaped nanostructures for the study of spin to charge inter-conversion using spin-orbit coupling in non-magnetic materials

Several spin–orbit effects allow performing spin to charge interconversion due to the spin Hall effects or the spin-momentum locking at Rashba interfaces and topological insulator surface states. Here, we focus on how these interconversions can be made electrically, using three different cross-shaped nanostructures. We apply the measurement configurations to the case of the spin Hall effect in Pt using CoFe electrodes to detect or inject spins. Both the direct and inverse spin Hall effects can be detected, with spin Hall signals up to two orders of magnitude higher than that of nonlocal measurements in metallic lateral spin valves, and with a much simpler fabrication protocol. We compare the respective signal amplitude of the three proposed geometries. Finally, we show that finite element method calculations allow extracting the spin Hall angle and the spin diffusion length of Pt from these measurements.

Numerical and experimental analysis on multi-pass conventional spinning of the cylindrical part with GH3030

Metal spinning, as a kind of rotary forming process, is widely applied in the production of various areas. In this paper, the mathematical model of the conchoid roller path is proposed based on the cylindrical part and applied in the experiments. The possible problems of the roller path and the product shape are verified by 2D simulation, while the 3D simulation is used to predict the product dimensions and defects. Based on the advantage of both 2D and 3D simulation, the flow of target product trial production is proposed. The simulation is verified by the experiments with hard-deformed superalloy GH3030. The crack mechanism of cylindrical part spinning process is studied with a combination of macro- and micro-methods. Results show that the forming effect of the conchoid roller path is good; the flow can reduce the trial production cost and time. The grain elongated obviously at the crack zone while metal accumulated at the edge of the product which is the main cause of the crack.

Spin-dependent transport characterization in metallic lateral spin valves using one-dimensional and three-dimensional modeling

We present the analysis of the spin signals obtained in NiFe based metallic lateral spin valves. We exploit the spin dependent diffusive equations in both the conventional 1D analytic modeling as well as in 3D Finite Element Method simulations. Both approaches are used for extracting the spin diffusion length $l_{sf}^{N}$ and the effective spin polarization $P_{eff}$ in Py/Al, Py/Cu and Py/Au based lateral nano-structures at both $300\,K$ and $77\,K$. Both the analytic modeling and 3D Finite Element Method simulations give consistent results. Combination of both models provides a powerful tool for reliable spin transport characterization in all metallic spin valves and gives an insight into the spin/charge current and spin accumulations 3D distributions in these devices. We provide the necessary ingredients to develop the 3D finite element modeling of diffusive spin transport.

Structural, elastic, mechanical, electronic, magnetic, thermoelectric and thermodynamic investigation of half metallic double perovskite oxide Sr2MnTaO6

Abstract Experimental lattice constant has been used for theoretical predictions on structural, elastic, mechanical, electronic magnetic thermoelectric and thermodynamic properties of Sr2MnTaO6 double perovskite oxide within well-known ab-initio density functional theory. Optimized lattice constant has been employed for obtaining spin involved electronic structure results within generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke Johnson approximation (mBJ). Electronic results show half-metallic nature with majority spin channels as metallic and minority spin channels as semi-conducting. Magnetic moment calculated within GGA + U was found equal to 4 µb. Calculated large value of Bulks modulus (B) and Young modulus (Y) characterize it as hard and stiffer material. Pugh ratio (B/G) and Cauchy pressure (C12–C44) portray its brittle nature. Using Boltztrap code we have calculated the variation of electrical conductivity (σ/τ), Seebeck coefficient (S), electronic thermal conductivity (k/τ) and Power factor (PF) in both spin channels. (σ/τ) is found to have decreasing nature in spin up states and increasing nature in spin down states, hence confirms the metallic nature in spin up states and semi-conducting in spin down states. Seebeck coefficients (S) reveal the presence of positive charge carriers in spin up states and negative in spin down states. The computed value of total power factor was found to be 1.99 × 1012 WK−2 m−1 s−1 at 1000 K. Furthermore, we have computed pressure and temperature dependent thermodynamic parameters for this compound in the temperature range of 0 K to 1000 K and pressure range of 0 GPa to 18 GPa with a step size of 3 GPa.

Study on Wall Heights and Surface Roughness of Spun Cups Produced of Metal Blanks by Multipass CNC Spinning Technology

This research paper deals with the influence analysis of the conventional metal spinning parameters (tool path profile tpp, tool feed f and mandrel rotational speed n) on the wall heights and the surface roughness Ra of the cylindrical-shaped spun parts measured in various directions with respect to the material rolling direction. Experimental research was carried out according to the 3-level full factorial design of experiment (DoE). Experimental study was also statistically analyzed by the ANOVA method. It was observed that tool path profile is a process parameter which has the most significant impact on the spun cup height and the surface finish, as well.

Structure, electronic, magnetic and optical properties of cubic Hf1-x(TM)xO2 (X = 0, 0.25, TM = Mn, Fe, Co, Ni): A first principle investigation

In the present work the structural, electronic, optical and magnetic properties of pure cubic HfO2and 3d transition metal (Mn, Fe, Co, Ni) doped (Hf1-xTMxO2) alloys (x = 0.25%) have been investigated by Density Functional Theory (DFT) as implemented in the FP-LAPW (full-potential augmented plane wave plus local orbital's) method employing generalized gradient approximation (GGA) and TB-mBJ exchange correlation methods. The calculated results such as lattice parameters and band gap are in good agreement with available experimental results. The calculation indicates that Hf1-xTMxO2 with x = 0 is a symmetric band gap semi-conductor but as a result of 3d TM doping, the band structure changes dramatically, presenting the half-metallic nature for all Hf1-x(TM)xO2 (x = 0.25, TM = Mn, Fe, Co, Ni) with majority spin states (spin up) as metallic and minority spin states (spin down) as semi-conducting for TM = Mn, Fe, Co and for TM = Ni the majority spin states (spin up) as semi-conducting and minority spin states (spin down) as metallic. The main contributions to the magnetic moment are mainly from the doped transition metals,TM = Mn, Fe, Co and Ni atoms with partial moments of 3.67 μB, 4.08 μB, 2.36 μB and 2.16 μB, respectively. From the charge density contour plots it was found that Hf0.75TM0.25O2 compounds have merged ionic and covalent character for the Hf–O and TM–O bonds. Further we have also explored the optical properties like reflectivity, index of refraction, energy loss, optical spectrum (absorption spectrum) corresponding to the imaginary part of dielectric function in the range 0–30 eV.

Quantitative and systematic analysis of bias dependence of spin accumulation voltage in a nondegenerate Si-based spin valve

Spin accumulation voltages in a non-degenerate Si spin valve are discussed quantitatively as a function of electric bias current using systematic experiments and model calculations. As an open question in semiconductor spintronics, the origin of the deviation of spin accumulation voltages measured experimentally in a non-degenerate Si spin valve is clarified from that obtained by model calculation using the spin drift diffusion equation including the effect of the spin-dependent interfacial resistance of tunneling barriers. Unlike the case of metallic spin valves, the bias dependence of the resistance-area product for a ferromagnet/MgO/Si interface, resulting in the reappearance of the conductance mismatch, plays a central role to induce the deviation.

Pressure-tuned Frustration of Magnetic Coupling in Elemental Europium.

Applying linear response and the magnetic force theorem in correlated density functional theory, the intersublattice exchange constants of antiferromagnetic Eu are calculated and found to vanish near the pressure of P_{c}=82 GPa, just where magnetic order is observed experimentally to be lost. The Eu 4f^{7} moment remains unchanged at high pressure, again in agreement with spectroscopic measurements, leaving the picture of perfect frustration of interatomic Ruderman-Kittel-Kasuya-Yoshida couplings in a broad metallic background, leaving a state of electrons strongly exchange coupled to arbitrarily oriented, possibly quasistatic local moments. This strongly frustrated state gives way to superconductivity at T_{c}=1.7 K, observed experimentally. These phenomena, and free energy considerations related to correlations, suggest an unusual phase of matter that is discussed within the scenarios of the Doniach Kondo lattice phase diagram, the metallic spin glass class, and itinerant spin liquid or spin gas systems.

Metallic spin-liquid-like behavior of LiV2O4

LiV$_2$O$_4$ spinel is known to exhibit heavy fermion-like behavior below a characteristic temperature $T_K\simeq 20$ K, while it preserves a paramagnetic state down to $T\sim10^{-2}$ K due to geometrical frustration. Here, it is shown that the dynamical spin susceptibility $\chi({\bf q},\omega)$ in LiV$_2$O$_4$ exhibits anomalous duality which is modeled as a sum of itinerant ($\chi_{\rm F}$) and local ($\chi_{\rm L}$) components,and that the local spin dynamics inferred from $\chi_{\rm L}({\bf q},\omega)$ is qualitatively different from that expected from time-averaged bulk properties. The anomaly coexists with the marginal Fermi liquid behavior inferred from the $-\ln T$ dependence of the electronic specific heat over a wide temperature range below $T_K$. We argue that such unusual properties of LiV$_2$O$_4$ can be attributed to the putative metallic spin liquid state emerging near the quantum critical point between spin glass and Fermi liquid states.

Haptic metal spinning

Sheet metal spinning is an incremental forming technique practiced for a long time only by experienced, skilled craftsmen. Over the last sixty years, attempts have been made to automate the process, but today the industrial practice still relies heavily on the skill of experienced operators. Complete analytical solutions to predict workpiece failure based on the path of the tool are not available, and finite element simulations of the process are too time-intensive to be of practical use for online toolpath correction. Therefore, today the design of toolpaths to avoid failure in spinning remains an art acquired by practice. In this paper, we approach the issue by designing an enhanced teach-in/playback system. We connect a haptic device to a CNC spinning machine; this device allows a human operator to control the working roller manually while feeling the force applied to the workpiece. Position, force and workpiece shape sensors allow collecting information on the toolpath followed by the operator and on its influence over the mechanics of the process. The opportunities offered by this system to derive rules for toolpath design are explored in two case studies on force control and wrinkling recovery, with new insights on the relationship between toolpaths and failure. A research agenda is outlined to exploit the full potential of haptic metal spinning.

Unsteady transport of MHD mixed convection inspired by thermal radiation and partial slip performance: Finite difference approach

Background: In this article mixed convection boundary layer flow of MHD fluid on permeable stretching surface is investigated under the effects of velocity and thermal slip. The physical unsteady problem is examined by considering thermal radiation effects on momentum and thermal boundary-layer flow. Different from available literature, in the present study we consider mix convective flow, thermal radiation, transverse applied magnetic field, velocity, and thermal slip. Methodology: The transform non-linear system of differential equation is tackled numerically by the aid of finite difference scheme named as Keller-Box. Stable solution is correct up to six decimal places and special cases overlaps with the existing results in literature validating the present analysis. Conclusion: It is concluded that mixed convection leads to accelerate fluid-flow and reduce temperature profile. Injection contributes in rising magnitude of velocity and temperature when compared with suction effects. Velocity and thermal slip parameter influence in lowering fluid-flow while temperature profile decrease for velocity slip parameter and opposite trend is witness corresponding to thermal slip parameter. Both velocity and temperature are increasing function of thermal radiation. In addition, the skin friction coefficient and the local Nusselt number are tabulated and analyzed. Novelty: Present study is concerned with fluid-flow applications in plastic films, polymer extrusion, glass fiber, metallurgical processes, and metal spinning.

Forming of Non-axisymmetric Products

Abstract The subject of this paper is to show the developed synchronous spinning machine for asymmetric products and the non-axisymmetric trial products manufactured by the developed method. Spinning is one of the metal forming processes used to produce hollow products from metal sheets and it is favorable for small- and medium-low production because the tools required are inexpensive. Spinning technology has been traditionally used to produce axisymmetric parts and it has been developed in recent years. Asymmetric spinning is a metal spinning method that can produce non-axisymmetric products. Trial spinning experiments of asymmetric sheet metal forming were successfully carried out by using the machine that was developed for this purpose. The developed machine can synchronize the radial and axial position of the roll with the spindle (mandrel).

Numerical Simulation of Stagger Spinning for D406A High-Strength Steel

Metal spinning process is widely used because of its low power requirement to producing complex symmetry components. In this paper, a modified 3D finite element(3D-FE) model is developed under the FE software environment based on characteristics of stagger spinning process. Analysis of the multi-pass spinning deformation mechanism and the effects of spinning parameters on spinning deformation is carried out. The results show that, large internal diameter of tube blank and low dimensional accuracy are caused by too little feed rate of spinning roller, especially for thin-walled tube. But if the feed rate is larger than 60mm/min, large spinning forces and instability appear. Strain rate and forming instability increase with the increase of rotational speed of mandrels, on the other hand, more obvious friction leads to bigger strain of surface of tube blank. With the radius of corner of spinning roller getting 13mm, the extensive overlaps lead to the improvement of spinning efficiency, while low forming quality accompanied by the large spinning forces occurs. Cutting phenomena leads to worse surface quality even tends to crack with the radius of corner of spinning roller being smaller than 8mm. An ideal combination of process parameters is obtained: the roller feed rate is 50mm/min, the rotational speed of mandrel is 40rad/min, the radius of corner of spinning roller is 10mm.

The effect of conventional metal spinning parameters on the spun-part wall thickness variation

Conventional metal spinning technology is based on the sequential shaping of a circular sheet over a mandrel through the action of a roller that produces localised pressure to produce a hollow axisymmetric product. The wall thickness of the formed part in this process is, in general, considered to be nearly constant, but in fact, a non-uniform distribution of wall thickness is observed. The wall thickness variation is a major defect found in produced parts that can cause part failure and therefore the spinning process must be properly optimized. This paper deals with the analysis of the chosen conventional metal spinning parameters (tool path profile, mandrel speed and the tool feed rate) on the wall thickness variation of cylindrical shaped spun-parts made of DC01 low carbon steel, while a three-level full factorial design of experiment method (DoE) and ANOVA (Analysis of Variance) were used. The experimental results revealed that tool path profile and the tool feed affects the wall thickness variation in a significant way. The effect of the mandrel speed was not clearly observed.

Forming of hemispherical and hemi-ellipsoidal parts of low carbon steel sheet by mandrel free metal spinning process

Metal spinning (MS) is an efficient and economical alternative method for low-volume functional sheet metal products. It has higher potential to shape three dimensional parts without employing matching die. The focus in advancement of shape forming shall bring an effective approach to produce defect free shapes and economically viable products. This paper is going to discuss about the modification in the MS process, without using matching dies or mandrel to produce a hemispherical and hemi-ellipsoidal profile product. The forming occurs by the deformation of sheet metal when the roller feed is against the rotating metal blank. Low carbon extra deep drawing Al killed steel sheets of thickness 1.6 mm were exploited as forming material. Further the paper illustrates on thickness variation, hardness, micro-structure, surface roughness and forming limit diagram (FLD) of the various zone of the formed part. It is examined that as the depth varies, the changes in thickness of formed part also varies. Also, the surface roughness was proportionally increased with increasing in percentage of reduction in thickness. In all zone of the formed steel part are in tension- tension strain conditions, there is no tension compression and plane strain condition occurred in the forming process. Due to this reason wrinkles failure is eliminated in die less MS process.

Magnetism of Bi2Se3 thin films with Eu-rich flat inclusions

We report the results of experimental and theoretical studies of Eu-doped Bi2Se3 thin films with extremely inhomogeneous distribution of magnetic component. The obtained electron microscopy images suggest that Eu atoms are concentrated within platelet-like nanoinclusions. The number of inclusions grows with the increase in Eu content, x. Moreover, at relatively high x values, the stacks of platelets (inclusions located one under another) become rather frequent. A comparative analysis of magnetic properties of the films under study reveals no pronounced changes of their temperature dependence with the increase in x, which, however, leads to the decrease in the average magnetic moment per Eu atom. A theoretical analysis of different mechanisms contributing to a possible magnetic ordering in the Eu-doped films demonstrates that at small distances (i.e. within a platelet) a dominant contribution is related to the RKKY interaction via electrons in the bulk, while the ordering at inter-platelet distances is governed by magnetic dipole–dipole interaction. The latter implies the antiferromagnetic ordering within the stacks of platelets explaining a drop of per Eu atom. We employ the model of a metallic spin glass to estimate the transition temperature, characterising the interaction within the ensemble of randomly distributed magnetic platelets. This estimate gives satisfactory agreement with the experiment, even if we take into account a finite film thickness, thus, neglecting the interaction anisotropy and including only the antiferromagnetism related to the stacking. While the overall contribution of interface Dirac electrons is damped in the systems under study, we argue that the obtained results can be used for the investigation of ultrathin films with analogous impurity profile, where this contribution should be clearly pronounced.

An MHD Effect on a Newtonian Fluid Flow Due to a Superlinear Stretching Sheet

The preliminary aim of this article is to investigate the effect of magnetohydrodynamic (MHD) flows of a viscous fluid due to a superlinear stretching sheet. These boundary layer flows arise in the industrial processes such as polymer extrusion processes, metal spinning, glass blowing and heat exchangers. The representing frameworks of highly nonlinear partial differential equations are mapped to nonlinear ordinary differential equations with a constant coefficient via similarity transformation and are solved analytically. The results are analyzed by means of various plots to provide the comparison and found to be in better agreement with the classical results of Crane and Pavlov. The viscous fluid due to a superlinear stretching sheet in the presence ofMHDhas enormous amount of nonlinearity in conducting the solution area with different arrangements.

Experimental Investigation on the Geometrical Accuracy of the CNC Multi-Pass Sheet Metal Spinning Process

The geometrical accuracy of multi-pass sheet metal spinning products is crucial in many applications. Aerospace, petroleum, and chemical industries motivated the development of modern spun components of complicated shapes with special functionality, but a substantial research lag exists behind this progress. Due to the localized plastic deformation involved, careful control of dimensions and form is required in spinning procedures. In this study, two sets of experiments were implemented for cup manufacturing using a retrofitted computer numerically controlled (CNC) spinning machine to identify the critical factors affecting product geometry and reveal their influence on the shape accuracy of the spun cups. The first set is a screening experiment to determine the most significant parameters and the second provides the optimum processing conditions affecting cup quality. The feed ratio, number of spin-forming passes, spinning ratio, and lubrication were found to have the most important effect on the geometry of the spun cups. Optimum quality with a higher processing speed (productivity) was achieved under a lubricated condition using a larger number of spin-forming passes at a high feed ratio, diminishing the commonly adopted rule of slow spinning for accurate products and reflecting a significance for state-of-the-art spinning practice. The findings of this paper introduce a basis for a spinning quality database.