Precessional dynamics of elemental moments in a ferromagnetic alloy

We demonstrate an element-specific measurement of magnetization precession in a metallic ferromagnetic alloy, separating Ni and Fe moment motion in Ni81Fe19. Pump-probe x-ray magnetic circular dichroism, synchronized with short magnetic field pulses, is used to measure free magnetization oscillations up to 2.6 GHz with elemental specificity and a rotational resolution of <2degrees. Magnetic moments residing on Ni sites and Fe sites in a Ni81Fe19(50 nm) thin film are found to precess together at all frequencies, coupled in phase within instrumental resolution of 90 ps.