The orbital Hall effect in light materials has attracted considerable attention for developing orbitronic devices. Here we investigate the orbital torque efficiency and demonstrate the switching of the perpendicularly magnetized materials through the orbital Hall material, i.e., Zr. The orbital torque efficiency of approximately 0.78 is achieved in the Zr orbital Hall material with the perpendicularly magnetized [Co/Pt]₃ sample, which significantly surpasses that of the perpendicularly magnetized CoFeB/Gd/CoFeB sample (approximately 0.04). Such a notable difference is attributed to the different spin-orbit correlation strength between the [Co/Pt]₃ sample and the CoFeB/Gd/CoFeB sample, confirmed through theoretical calculations. Furthermore, the full magnetization switching of the [Co/Pt]₃ samples with a switching current density of approximately 2.6×10⁶A/cm² has been realized through Zr, which even outperforms that of the W spin Hall material. Our finding provides a guideline to understand orbital torque efficiency and paves the way for developing energy-efficient orbitronic devices.

The utilization of terahertz (THz) emission spectroscopy in femtosecond photoexcited spintronic heterostructures has emerged as a versatile tool for investigating ultrafast spin-transport in a non-contact and non-invasive manner. However, the investigation of ultrafast orbital-transport is still in the primitive stage. Here, we experimentally demonstrate the orbital-to-charge current conversion in Co/Zr/Al₂O₃ heterostructures. Our experimental results indicate a photoinduced orbital current (J_L) from Co propagating through Zr layer with a long-distance ballistic transport and a velocity of ~\(0.27\)± \(0.02 \, {{\rm{nm}}} \, {{{\rm{fs}}}}^{-1}\). On the one hand, we demonstrate a critical pump fluence required to overcome the collisions in orbital transport, enabling a swifter flow of J_L. On the other hand, a critical temperature is observed, below which the orbital transport is impeded. Finally, we observe a nearly 2.95-fold enhancement in the THz emission due to an additional conversion of the spin-to-orbital current conversion from a 1 nm thick W-insertion layer between Co and Zr layers. Our results pave the way for designing promising opto-spin-orbitronic devices and THz emitters.

Efficiently manipulating the magnetization of van der Waals (vdW) ferromagnets has attracted considerable interest in developing room-temperature two-dimensional (2D) material-based memory and logic devices. Here, taking advantage of the unique properties of the vdW ferromagnet as well as promising characteristics of the orbital Hall effect, we demonstrate the room-temperature magnetization switching of vdW ferromagnet Fe₃GaTe₂ through the orbital torque generated by the orbital Hall material, Titanium (Ti). The switching current density is estimated to be around 1.6×10⁶A/cm², comparable to that achieved in Fe₃GaTe₂ using spin-orbit torque from spin Hall materials (e.g., WTe₂, and TaIrTe₄). The efficient magnetization switching arises from the combined effects of the large orbital Hall conductivity of Ti and the strong spin-orbit correlation of the Fe₃GaTe₂, as confirmed through theoretical calculations. Our findings advance the understanding of orbital torque switching and pave the way for exploring 2D material-based orbitronic devices.

The use of voltage induced strain to switch magnetic tunnel junctions (MTJs) is a promising solution for reducing the switching energy in MRAM technologies. The MTJ is integrated with a piezoelectric layer to generate the strain. A very thin layer is needed to switch with small voltages and small energy dissipation. It is challenging to synthesize ultrathin piezoelectric layers that retain a high degree of piezoelectricity. An alternate approach is to use time-varying strain generated by a surface acoustic wave (SAW). This approach does not require a thin piezoelectric layer since the SAW is confined to the surface of the layer. In this study, we fabricated in-plane MTJs on piezoelectric LiNbO3 substrates and used IDTs to generate the SAW signal within the substrate. Our results showed that the SAW signal had a significant influence on the resistance and the tunneling magnetoresistance (TMR) ratio of the MTJs. The influence was much less significant in nanometer size MTJs than in micrometer sized ones. Most surprisingly, the SAW signal caused the tunneling magnetoresistance ratio (TMR) to drop below zero for the micrometer size MTJ, meaning that the antiparallel resistance RAP is temporarily less than the parallel resistance RP under SAW excitation. Our results provide insight into the dynamic behavior of MTJs under periodic strain and the dependence of this behavior on the device dimensions as they are scaled down to nanometer sizes.