Sub-THz High Spin Precession Frequency in van der Waals Ferromagnet FeGaTe.

The 2D magnet FeGaTe has received considerable attention for its high Curie temperature (), robust intrinsic ferromagnetism, and significant perpendicular magnetic anisotropy (PMA). In this study, the dynamic magnetic properties of FeGaTe are systematically investigated using an all-optical pump-probe technique. We find that the spin precession frequency () is as high as 351.

Anisotropic phonon dynamics in Dirac semimetal PtTe thin films enabled by helicity-dependent ultrafast light excitation.

Coherent phonons have aroused considerable attention in condensed matter physics owing to their extraordinary capacity of reflecting and controlling the physical properties of matter. However, the investigation on the interaction between coherent phonons and other microscopic particles on the ultrafast timescale within topological systems continues to be an active and unresolved area. Here, we show the energy transfer of coherent optical phonons (COP) in Dirac semimetal PtTe thin films using ultrafast optical pump-probe spectroscopy.

Temperature-Dependent Spin-to-Charge Conversion and Efficient Manipulation of Elliptical THz Waves in BiTe/TbFeCo Heterostructures.

Topological insulators (TIs) with spin-momentum-locked surface states and considerable spin-to-charge conversion (SCC) efficiency are ideal substitutes for the nonmagnetic layer in the traditional ferromagnetic/nonmagnetic (FM/NM) spintronic terahertz (THz) emitters. Here, the TI/ferrimagnetic structure as an effective polarization tunable THz source is verified by terahertz emission spectroscopy. The emitted THz electric field can be separated into two THz components utilizing their opposite symmetry on pump polarization and the magnetic field.

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets.

Spintronic terahertz (THz) emitters based on synthetic antiferromagnets (SAFs) of FM/Ru/FM (FM: ferromagnet) have shown great potential for achieving coherent superposition and significant THz power enhancement due to antiparallel magnetization alignment. However, key issues regarding the effects of interlayer exchange coupling and net magnetization on THz emissions remain unclear, which will inevitably hinder the performance improvement and practical application of THz devices. In this work, we have investigated the femtosecond laser-induced THz emission in Pt (3)/CoFe (3)/Ru ( = 0-3.

Significant Reorientation Transition of Magnetic Damping Anisotropy in CoFeAl Heusler Alloy Films at Low Temperatures.

The temperature () dependences of magnetization dynamics, especially for magnetic damping anisotropy, have been systematically investigated in well-ordered CoFeAl films with a biaxial anisotropy. It is found that the damping anisotropy factor , defined as the fractional difference of damping between the hard and easy axes, changes from 0.35 to -0.

Ferromagnetic resonance modes of a synthetic antiferromagnet at low magnetic fields.

One key advantage of antiferromagnets over ferromagnets is the high magnetic resonance frequencies that enable ultrafast magnetization switching and oscillations. Among a variety of antiferromagnets, the synthetic antiferromagnet (SAF) is a promising candidate for high-speed spintronic devices design. In this paper, micromagnetic simulations are employed to study the resonance modes in an SAF structure consisting of two identical CoFeB ferromagnetic (FM) layers that are antiferromagnetically coupled via interlayer exchange coupling.

Controllable magnetization precession dynamics and damping anisotropy in CoFeAl Heusler-alloy films.

Magnetization dynamics of the epitaxially-grown CoFeAl (CFA) thin films have been systematically investigated by the time-resolved magneto-optical Kerr effect (TR-MOKE). The dependences of precession frequency f, relaxation time τ and magnetic damping factor α upon the orientation of applied magnetic field are found to have a strong four-fold symmetry. Two series of samples with various substrate temperatures (T) and thickness (t) were prepared and a large Gilbert damping difference between the hard and easy axes is extracted to be 3.

Temperature Dependence of Spin-Orbit Torques in Nearly Compensated TbCo Films by a Topological Insulator SbTe.

Topological insulators (TIs) with spin-momentum-locked metallic surface states can exert giant spin-orbit torques, offering great potential in energy-efficient magnetic memory devices. In this work, temperature ()-dependent SOT efficiencies are investigated in SbTe/Ta/TbCo heterostructures with perpendicular magnetic anisotropy. The spin Hall angle θ is around 0.

Large anisotropy of magnetic damping in amorphous CoFeB films on GaAs(001).

Amorphous CoFeB films grown on GaAs(001) substrates demonstrating significant in-plane uniaxial magnetic anisotropy were investigated by vector network analyzer ferromagnetic resonance. Distinct in-plane anisotropy of magnetic damping, with a largest maximum-minimum damping ratio of about 109%, was observed via analyzing the frequency dependence of linewidth in a linear manner. As the CoFeB film thickness increases from 3.

Free Field Electric Switching of Perpendicularly Magnetized Thin Film by Spin Current Gradient.

To realize high-speed nonvolatile magnetic memory with low energy consumption, electric switching of perpendicular magnetization by spin-orbit torque in the heavy metal/ferromagnetic (HM/FM) structure has recently attracted intensive attention. Conventionally, an external in-plane magnetic field for breaking the symmetry is required for achieving electric switching of perpendicular magnetization. However, electric switching without external field is the prerequisite for the integration of magnetic functionality into the integrated circuit devices.

Magnetic precession modes with enhanced frequency and intensity in hard/NM/soft perpendicular magnetic films.

High frequency magnetic precessions with strong intensity are strongly desired in material systems for high performance magnetic memory or nano-oscillator applications with ultrafast manipulation speed. Here, we demonstrate an exchange-coupled asymmetric composite film structure of Ta/Pd/[Pd/Co]/Cu(t)/[Co/Ni]/Ta with adjustable strong perpendicular magnetic anisotropy and interlayer coupling strength, in which the dynamic magnetic properties are systematically studied by using time-resolved magneto-optical Kerr effect spectroscopy. It is demonstrated that the in-phase precession frequency is between those of the single hard magnetic [Pd/Co] and soft [Co/Ni] multilayers, which can be significantly enhanced for the strongly coupled case at t < 1 nm.

Controllable Interfacial Coupling Effects on the Magnetic Dynamic Properties of Perpendicular [Co/Ni]/Cu/TbCo Composite Thin Films.

Dynamic magnetic properties in perpendicularly exchange-coupled [Co/Ni]/Cu (t = 0-2 nm)/TbCo structures show strong dependences on the interfacial antiferromagnetic strength J, which is controlled by the Cu interlayer thickness. The precession frequency f and effective damping constant α of a [Co/Ni] multilayer differ distinctly for parallel (P) and antiparallel (AP) magnetization orientation states. For samples with a thin t, f of the AP state is apparently higher, whereas α is lower than that in the P state, owing to the unidirectional exchange bias effect (H) from the TbCo layer.

Wafer-Scale Fabrication of Suspended Single-Walled Carbon Nanotube Arrays by Silver Liquid Dynamics.

Suspended single-walled carbon nanotubes (SWNTs) have advantages in mechanical resonators and highly sensitive sensors. Large-scale fabrication of suspended SWNTs array devices and uniformity among SWNTs devices remain a great challenge. This study demonstrates an effective, fast, and wafer-scale technique to fabricate suspended SWNT arrays, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between the prefabricated palladium electrodes in high temperature annealing treatment.

Magnetization switching by combining electric field and spin-transfer torque effects in a perpendicular magnetic tunnel junction.

Effective manipulation of magnetization orientation driven by electric field in a perpendicularly magnetized tunnel junction introduces technologically relevant possibility for developing low power magnetic memories. However, the bipolar orientation characteristic of toggle-like magnetization switching possesses intrinsic difficulties for practical applications. By including both the in-plane (T//) and field-like (T⊥) spin-transfer torque terms in the Landau-Lifshitz-Gilbert simulation, reliable and deterministic magnetization reversal can be achieved at a significantly reduced current density of 5×10(9) A/m(2) under the co-action of electric field and spin-polarized current, provided that the electric-field pulse duration exceeds a certain critical value τc.

Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films.

Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability.

Interfacial exchange coupling and magnetization reversal in perpendicular [Co/Ni]N/TbCo composite structures.

Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo(100-x) alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo(100-x) alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo(100-x) or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer.

Role of TbFe on Perpendicular Magnetic Anisotropy and Giant Magnetoresistance Effect in [Co/Ni]-Based Spin Valves.

The exchange-coupled [Co/Ni]/TbFe nano-magnetic films can display strong perpendicular magnetic anisotropy (PMA) which depends on the Tb:Fe component ratio, TbFe layer thickness and the repetition number N of [Co/Ni] multilayer. Perpendicular spin valves in the nano thickness scale, consisting of a [Co/Ni] free and a [Co/Ni]/TbFe reference multilayer, show high giant magnetoresistance (GMR) signal of 6.5 % and a large switching field difference over 3 kOe.