Colossal magnetoresistance in manganites and related prototype devices

We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb：SrTio3 p-n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.

Voltage-controllable magnetic skyrmion dynamics for spiking neuron device applications

Voltage-controlled magnetic skyrmions have attracted special attention because they satisfy the requirements for well-controlled high-efficiency and energy saving for future skyrmion-based neuron device applications.In this work,we propose a compact leaky-integrate-fire(LIF)spiking neuron device by using the voltage-driven skyrmion dynamics in a multiferroic nanodisk structure.The skyrmion dynamics is controlled by well tailoring voltage-induced piezostrains,where the skyrmion radius can be effectively modulated by applying the piezostrain pulses.Like the biological neuron,the proposed skyrmionic neuron will accumulate a membrane potential as skyrmion radius is varied by inputting the continuous piezostrain spikes,and the skyrmion radius will return to the initial state in the absence of piezostrain.Therefore,this skyrmion radius-based membrane potential will reach a definite threshold value by the strain stimuli and then reset by removing the stimuli.Such the LIF neuronal functionality and the behaviors of the proposed skyrmionic neuron device are elucidated through the micromagnetic simulation studies.Our results may benefit the utilization of skyrmionic neuron for constructing the future energy-efficient and voltage-tunable spiking neural networks.

Strain-mediated magnetoelectric control of tunneling magnetoresistance in magnetic tunneling junction/ferroelectric hybrid structures

Because of the wide selectivity of ferromagnetic and ferroelectric(FE)components,electric-field(E-field)control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures.Here,an MgO-based magnetic tunnel junction(MTJ)is chosen rationally as the ferromagnetic constitution and a high-activity(001)-Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_(3)(PMN-0.3PT)single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure.The shape of tunneling magnetoresistance(TMR)versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias.The E-field-controlled change in the TMR ratio is up to-0.27%without magnetic-field bias.Moreover,when a typical magnetic field(~±10 Oe)is applied along the minor axis of the MTJ,the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias.This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ.In addition,based on such a multiferroic heterostructure,a strain-gauge factor up to approximately 40 is achieved,which decreases further with a sign change from positive to negative with increasing magnetic fields.This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.

Modulation of spin dynamics in Ni/Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3) multiferroic heterostructure

Motivated by the fast-developing spin dynamics in ferromagnetic/piezoelectric structures, this study attempts to manipulate magnons (spin-wave excitations) by the converse magnetoelectric (ME) coupling. Herein, electric field (E-field) tuning magnetism, especially the surface spin wave, is accomplished in Ni/0.7Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.3PbTiO_(3) (PMN-PT) multiferroic heterostructures. The Kerr signal (directly proportional to magnetization) changes of Ni film are observed when direct current (DC) or alternative current (AC) voltage is applied to PMN-PT substrate, where the signal can be modulated breezily even without extra magnetic field (H-field) in AC-mode measurement. Deserved to be mentioned, a surface spin wave switch of “1” (i.e., “on”) and “0” (i.e., “off”) has been created at room temperature upon applying an E-field. In addition, the magnetic anisotropy of heterostructures has been investigated by E-field-induced ferromagnetic resonance (FMR) shift, and a large 490 Oe shift of FMR is determined at the angle of 45° between H-field and heterostructure plane.

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.

Deterministic reversal of single magnetic vortex circulation by an electric field

The ability to control magnetic vortex is critical for their potential applications in spintronic devices.Traditional methods including magnetic field,spin-polarized current etc.have been used to flip the core and/or reverse circulation of vortex.However,it is challenging for deterministic electric-field control of the single magnetic vortex textures with time-reversal broken symmetry and no planar magnetic anisotropy.Here it is reported that a deterministic reversal of single magnetic vortex circulation can be driven back and forth by a space-varying strain in multiferroic heterostructures,which is controlled by using a bi-axial pulsed electric field.Phase-field simulation reveals the mechanism of the emerging magnetoelastic energy with the space variation and visualizes the reversal pathway of the vortex.This deterministic electric-field control of the single magnetic vortex textures demonstrates a new approach to integrate the low-dimensional spin texture into the magnetoelectric thin film devices with low energy consumption.

Improving solar control of magnetism in ternary organic photovoltaic system with enhanced photo-induced electrons doping

§The growing demand for storage space has promoted in-depth research on magnetic performance regulation in an energy-saving way.Recently,we developed a solar control of magnetism,allowing the magnetic moment to be manipulated by sunlight instead of the magnetic field,current,or laser.Here,binary and ternary photoactive systems with different photon-to-electron conversions are proposed.The photovoltaic/magnetic heterostructures with a ternary system induce larger magnetic changes due to higher short current density(J SC)(20.92 mA·cm^(−2))compared with the binary system(11.94 mA·cm^(−2)).During the sunlight illumination,ferromagnetic resonance(FMR)shift increases by 80%(from 169.52 to 305.48 Oe)attributed to enhanced photo-induced electrons doping,and the variation of saturation magnetization(M S)is also amplified by 14%(from 9.9%to 11.3%).Furthermore,photovoltaic performance analysis and the transient absorption(TA)spectra indicate that the current density plays a major role in visible light manipulating magnetism.These findings clarify the laws of sunlight control of magnetism and lay the foundation for the next generation solar-driven magneto-optical memory applications.