Speaker
Description
The observation of ultrafast manipulation and coherent control of spins in magnetic materials at room temperature has prompted the intense experimental and theoretical efforts to understand the underlying microscopic mechanisms and relevant interactions (exchange, spin-lattice, electron-phonon, coulomb etc.) driving such magnetic phenomena at picosecond timescales.
Stoichiometric B2 ordered epitaxial (001) FeRh undergoes a first order magnetic phase transition from antiferromagnetic (AFM) to ferromagnetic(FM) at ≈ 380K. In the AFM phase of FeRh, only Fe has net magnetic moment, whereas in the FM phase both Fe and Rh carry net moments. The phase transition is also accompanied by a ≈ 1% isotropic lattice expansion in the bulk BCC structure, and changes in electronic structure. The phase transition has been extensively studied theoretically and experimentally, in thermal equilibrium and in the time domain, but a precise understanding of the roles of the electronic, phononic and spin sub-systems remains elusive.
In this contribution, I will discuss the coherent surface phonon spectroscopy of optically induced phase transition in FeRh studied via coherent XUV diffuse scattering in reflection geometry at DiProI beamline at FERMI-FEL. The square shaped scattering pattern and dispersion curves show the biaxial anisotropic nature of surface acoustic wave (SAW) propagation, with different phase velocities along different crystallographic axes, in epitaxial FeRh thin films grown on single crystalline 3C-SiC. Further, time-frequency wavelet analysis of SAW phonon oscillations shows the nature of structural phase transition in FeRh. This study marks the demonstration of comprehensive and simple method of SAW analysis using XUV scattering in technologically important phase transition materials such as FeRh at such high wavevectors.