Probing Nonequilibrium Phonon-Magnon Coupling in Emerging Functional Materials with Femtosecond Transient Thermal and Spin Grating Spectroscopy
Abstract
We propose the development of a state-of-the-art transient grating spectroscopy setup that can flexibly generate periodic thermal and spin excitations with sub-picosecond time resolution and diffraction-limited spatial resolution. The key strength of this system is that it can selectively excite phonons (quantized lattice vibrations) or magnons (quantized spin waves) with specific wavelength and monitor the interaction between the excited population and other energy carriers in the same material with simultaneous high spatial and temporal resolutions. Phonons are major heat carriers and magnons are responsible for transporting magnetization in magnetic solids. The interaction between phonons and magnons is the origin of many technologically relevant processes, such as magnetoelasticity, magnetocaloric effect, spin Seebeck effect and the dissipation processes in spintronic devices. Cooling and energy conversion technologies based on magnetocaloric and magnetoelastic effect and next-generation communication and computing technologies based on spintronics are an important part of the DoD portfolio and can have important applications relevant to defense and national security. In particular, interaction of phonons and magnons when they are driven away from their local equilibrium is the key to understanding energy and information transport processes in these applications. However, current understanding of nonequilibrium phonon-magnon coupling is largely qualitative due to the lack of suitable experimental probes, which has hindered further development of materials and devices with desirable efficiency. We propose to develop an ultrafast optical spectroscopy system with the unique capability of separately exciting phonons or magnons with controlled wavelength and monitoring their subsequent evolution with high spatial-temporal resolution. This system uses two crossed laser beams with controlled polarizations: parallel polarization generates a periodic intensity grating, which can thermally couple to phonons in the sample whereas orthogonal polarization generates a periodic circular polarization grating, which can couple to magnons in the same sample. The two modes can be conveniently switched using a half waveplate. This system will also include a cryogen-free low temperature testing system, which will allow the investigation of phononmagnon interaction in novel magnetic phases, for example the skyrmion phase in chiral magnets. We plan to apply this state-of-the-art system to study 1) the influence of the microstructures on phonon-magnon coupling in functional intermetallic compounds such as half-heusler/heusler solid solutions, which are important magnetocaloric and magnetoelastic materials, 2) the coupling of flexural phonons and magnons in two-dimensional magnets, such as CrI3 and 3) coupled lattice and magnetization dynamics in skyrmion phases in chiral magnets. This requested equipment will be of critical importance in understanding the processes of heat and spin interconversion in emerging functional materials and in designing future compact, integrated cooling, energy conversion and communication technologies. In addition, access to this new capability will help educate and train many graduate students and postdocs in experimental nonlinear and ultrafast optics and thermal-magnetic characterization of materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010161
Entities
People
- Bolin Liao
Organizations
- Army Contracting Command
- United States Army
- University of California, Santa Barbara