Transient spatio-temporal domain patterns in permalloy microstructures induced by fast magnetic field pulses

The response of multidomain flux-closure structures (Landau states) in micrometer-scale magnetic thin-film elements upon fast magnetic field pulses leads to the excitation of magnetic eigenmodes and to short-lived domain patterns that do not occur in quasi-static remagnetisation. Such transient spatio-temporal patterns and particular detail features are discussed. Examples are presented for permalloy platelets of various shapes and sizes. Dynamic series of domain patterns with variable delay between field pulse and photon pulse (synchrotron radiation) have been taken using stroboscopic XMCD-PEEM. Precessional remagnetisation starts at the domain boundaries. The damped precessional motion propagates into the domains magnetised perpendicular to the field pulse. Further, an apparent dynamical broadening of domain boundaries, the formation of transient vortices and domain walls as well as the fast formation of blocking patterns are discussed. An important feature is the action of the demagnetising field that develops via the damped precessional motion of the magnetisation on the nanosecond time scale. The effective field is constituted by the sum of the instantaneous external pulse field and the delayed response of the demagnetising field.