Macroscopic, layered onion shell like magnetic domain structure generated in YIG films using ultrashort, megagauss magnetic pulses

Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simulations show that the giant magnetic field pulses create ultrafast terahertz (THz) spin waves and a snapshot of these fast-propagating spin waves is stored as the layered onion shell shaped domains in the YIG film. Typically, information transport via spin waves in magnonic devices occurs in the gigahertz regime, where devices are susceptible to thermal disturbances at room temperature. Our intense laser light pulse-YIG sandwich target combination, paves the way for room temperature table-top THz spin wave devices, operating just above or in the range of the thermal noise floor. This dissipation-less device offers ultrafast control of spin information over distances of few hundreds of microns.