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Dr. Junjie He

Fields of interest

2D magnetic materials & heterostructures

Real-time spin dynamics

PublicationsGoogle scholar


Photo-induced real time spin dynamics in 2D magnets

Laser-induced switching of spins in materials is of great interest to revolutionize future magnetic storage technology and spintronics, which is generally realized in multicomponent ferrimagnetic (FiM) compounds but rare in 2D magnets. Using density functional theory (DFT) calculations, we show that 2D MXenes of type Cr2VC2F2  have unusual FiM order. Interestingly, our real-time time-dependent DFT simulations demonstrate that laser pulses can directly induce ultrafast spinselective charge transfer between magnetic sublattices in a few femtoseconds and further generate dramatic changes in the magnetic structure of these MXenes, including a transition from FiM to transient ferromagnetism (FM). The microscopic mechanism behind this ultrafast switching of spin is governed by the optically induced intersite spin transfer (OISTR) effect, which theoretically enables the ultrafast optical manipulation of the magnetic state in MXenes.

Research Project by DFG

Exploring the light-induced interlayer spin transfer (i.e., spin-dependent charge transfer) dynam-ics and optical manipulation of magnetic properties in 2D magnetic vdW heterostructures is of great importance for both fundamental scientific interest and many potential applications in op-toelectronics and spintronics. It is crucial to understand the current experiment for light-tunable properties, for instance, optical control of valley splitting and magnetism in WSe2/CrI3 heterostructures.[36,38] On the other hand, ultrafast optical manipulation of interlayer exchange coupling and magnetic anisotropy has enabled widely used magnetic storage technologies.. However, to the best of my knowledge, the theoretical modeling of photo-exited dynamics be-havior for 2D magnetic vdW heterostructures still remains relatively unexplored. There are plen-ty of choices of 2D magnets with diverse magnetic and electronic structure, ranging from FM metals, FM semiconductors, to AFM semiconductors, some of which exhibit nontrivial topologi-cal properties. Controlling the stacking degrees of freedom of these 2D magnets can create a number of new heterostructures with distinct magnetic order.

The goal of the project is to explore the ultrafast control of interlayer spin-dependent charge transfer and magnetic properties in a large variety of 2D magnets and vdW heterostructures by combination with the DFT for ground-state properties calculations and real-time TDDFT for photo-excited dynamics simulations.