Grain refinement of as-cast superalloy IN718 under action of low voltage pulsed magnetic field

The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.

Voltage control magnetism and ferromagnetic resonance in an Fe_(19)Ni_(81)/PMN-PT heterostructure by strain

Voltage control magnetism has been widely studied due to its potential applications in the next generation of information technology.PMN-PT,as a single crystal ferroelectric substrate,has been widely used in the study of voltage control magnetism because of its excellent piezoelectric properties.However,most of the research based on PMN-PT only studies the influence of a single tensile(or compressive)stress on the magnetic properties due to the asymmetry of strain.In this work,we show the effect of different strains on the magnetic anisotropy of an Fe_(19)Ni_(81)/(011)PMN-PT heterojunction.More importantly,the(011)cut PMN-PT generates non-volatile strain,which provides an advantage when investigating the voltage manipulation of RF/microwave magnetic devices.As a result,a ferromagnetic resonance field tunability of 70 Oe is induced in our sample by the non-volatile strain.Our results provide new possibilities for novel voltage adjustable RF/microwave magnetic devices and spintronic devices.

Influence of the low voltage pulsed magnetic field on the columnar-to-equiaxed transition during directional solidification of superalloy K4169

The low voltage pulsed magnetic field(LVPMF)disrupts the columnar dendrite growth,and the columnarto-equiaxed transition(CET)occurs during the directional solidification of superalloy K4169.Within the pulse voltage ranging from 100Vto 200 V,a transition from columnar to equiaxed grain was observed,and the grain size decreased as the pulse voltage rised.As the pulse frequency increased,the CET occurred,and the grains were refined.However,the grains became coarse,and the solidification structure was columnar crystal again when frequency increased to 10 Hz.The LVPMF had an optimal frequency to promote CET.The LVPMF on the CET was affected by the withdrawal speed and increasing the withdrawal speed enhances the CET.The distribution of electromagnetic force and flow field in the melt under the LVPMF were modeled and simulated to reveal the CET mechanism.It is considered that the CET should be attributed to the coupling effects of magnetic vibration and melt convection induced by the LVPMF.

Voltage assisted control of spin-transfer nano-oscillators

The spin-transfer nano-oscillator （STNO） has recently acquired a huge amount of research interest, due to its promising easy tunability along with the miniature size. The output frequency control of an STNO through magnetic field and current has been examined almost to its full extent; however, there are issues that still need to be addressed. Here, we propose a novel way of voltage control of the output frequency of an STNO, and alongside reducing its power requirement.

Optimizing magneto-ionic performance in structure/composition-engineered ternary nitrides

Magneto-ionics,an emerging approach to manipulate magnetism that relies on voltage-driven ion motion,holds the promise to boost energy efficiency in information technologies such as spintronic devices or future non-von Neumann computing architectures.For this purpose,stability,reversibility,endurance,and ion motion rates need to be synergistically optimized.Among various ions,nitrogen has demonstrated superior magneto-ionic performance compared to classical species such as oxygen or lithium.Here,we show that ternary Co_(1−x)Fe_(x)N compound exhibits an unprecedented nitrogen magneto-ionic response.Partial substitution of Co by Fe in binary CoN is shown to be favorable in terms of generated magnetization,cyclability and ion motion rates.Specifically,the Co_(0.3)5Fe_(0.65)N films exhibit an induced saturation magnetization of 1,500 emu/cm^(3),a magneto-ionic rate of 35.5 emu/(cm^(3)·s)and endurance exceeding 10^(3) cycles.These values significantly surpass those of other existing nitride and oxide systems.This improvement can be attributed to the larger saturation magnetization of Co_(0.35)Fe_(0.65) compared to individual Co and Fe,the nature and size of structural defects in as-grown films of different composition,and the dissimilar formation energies of Fe and Co with N in the various developed crystallographic structures.

Continuous and fast magneto-ionic control of magnetism in Ta/Co/ BiFeO_(3)/SrRuO_(3) multiferroic heterostructure

Room temperature electric field controlled magnetism is extremely promising for the next-generation high-performance spintronic devices.Here,based on the ferroelectric switching driven oxygen ion migration in the Ta/Co/BiFeO_(3)/SrRuO_(3) heterostructures,the magnetic moment,magnetic coercive field,exchange bias field,and junction resistance are reversibly manipulated by tuning the ferroelectric polarization of the BiFeO_(3) layer.All these phenomena are consistently explained by the oxygen ion migration induced CoOx/Co redox effect,which is evidenced by the synchrotron X-ray absorption spectroscopy measurements.Interestingly,owing to the controllable ferroelectric switching dynamics of the BiFeO_(3) thin film,the magnetic coercive field of the Co thin film can be continuously and precisely tuned by controlling the ferroelectric polarization of the BiFeO_(3) thin film,and the manipulating speed of the voltage control of magnetism can be fast to 100 ns.This nonvolatile,stable,reversible,fast,and reproducible voltage control of magnetism shows great potential for designing low-power and high-speed spintronics.