Element-specific and high-bandwidth ferromagnetic resonance spectroscopy with a coherent, extreme ultraviolet (EUV) source

We developed and applied a tabletop, ultrafast, high-harmonic generation (HHG) source to measure the element-specific ferromagnetic resonance (FMR) in ultra-thin magnetic alloys and multilayers on an opaque Si substrate. We demonstrate a continuous wave bandwidth of 62 GHz, with promise to extend to 100 GHz or higher. This laboratory-scale instrument detects the FMR using ultrafast, extreme ultraviolet (EUV) light, with photon energies spanning the M-edges of most relevant magnetic elements. An RF frequency comb generator is used to produce a microwave excitation that is intrinsically synchronized to the EUV pulses with a timing jitter of 1.4 ps or better. We apply this system to measure the dynamics in a multilayer system as well as Ni-Fe and Co-Fe alloys. Since this instrument operates in reflection-mode, it is a milestone toward measuring and imaging the dynamics of the magnetic state and spin transport of active devices on arbitrary and opaque substrates. The higher bandwidth also enables measurements of materials with high magnetic anisotropy, as well as ferrimagnets, antiferromagnets, and short-wavelength (high wavevector) spinwaves in nanostructures or nanodevices. Furthermore, the coherence and short wavelength of the EUV will enable extending these studies using dynamic nanoscale lensless imaging techniques such as coherent diffractive imaging, ptychography, and holography.