Stroboscopic Small Angle Neutron Scattering Investigations of Microsecond Dynamics in Magnetic Nanomaterials

Abstract

Time-resolved Small Angle Neutron Scattering (SANS) techniques have recently been developed that allow ordering and relaxation processes of magnetic moments in nanoparticles to be monitored. In stroboscopic experiments, time-frame data acquisition has been synchronized with a periodic external magnetic field. Slow relaxation of magnetic particle moments onto equilibrium has been studied in periods of the order of 30 s after switch off a static field. By applying a sine-wave modulated magnetic field at frequencies above 50 Hz, the time-resolved SANS response to a forced oscillation could be analyzed. When a continuous neutron flux was used in conventional SANS, the shortest accessible time range was limited to about 3 ms resulting from the wavelength spread. A breakthrough of time resolution into the micro-second range was achieved with the pulsed frame overlap TISANE technique, which allows us to exploit a dynamical range similar to that of X-ray photon-correlation spectroscopy.