Single laser pulse induced dynamic magnetization reversal mechanism of perpendicularly magnetized L1 FePt films

Abstract

In order to measure photoinduced dynamic magnetization reversal by single laser pulse, alternating magnetic field is synchronized with the femtosecond laser pulse such that the magnetization state is reset before each single laser pulse. For perpendicularly magnetized L10 FePt films, the dynamic magnetization reversal process is accompanied by the nucleation of reversed domains and the barrierless transient domain wall motion at low magnetic fields and subsequent pinned domain wall motion at the switching field. The switching field does not change with the pump-probe delay time.

Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

“…For extended in-plane magnetized thin film samples, switching typically occurs by means of a thermally activated local nucleation process of a reverse domain that then expands through the sample via transient domain states after domain wall depinning. 17,49,51 So, even though the switching segment of the magnetization reversal process away from the HA is associated with non-uniform transient states, i.e., a dynamic reversal sequence, these states are neither stable nor metastable. Thus, on the quasi-static time scale that we analyzed here, ideal ferromagnetic films with uniaxial in-plane anisotropy are characterized by uniform magnetization states only and static, stable, or meta-stable domain states do not exist.…”

“…This type of shape has been previously observed in highly ordered uniaxial samples. 17,49,51 It indicates a magnetization reversal through a combination of domain nucleation followed by domain wall depinning and rapid propagation for field orientations near the EA. This behavior changes into a coherent rotation reversal for field values H ffi H c upon approaching the HA orientation of the applied magnetic field, simply because the field axis magnetization component reaches its zero value before a switch actually occurs.…”

“…21,46,61 On the other hand, many studies have been performed for the purpose of analyzing the magnetization reversal mechanism in individual ferromagnetic films, including magnetic alloy films. 20,22,26,28,36,42,44,45,49,51,52,55,57 Hereby, many works have been focused on alloys made from 4d/5d transition metals and 3d elemental ferromagnets 14,26,42,49 or alloys of 4f elements with 3d elemental ferromagnets. 17,22,55 These types of alloys, besides having other interesting features, can lead to large magnetocrystalline anisotropies 14 as well as to unconventional magnetic phase transitions as a function of temperature.…”

“…As a consequence of this complexity, magnetization reversal may follow different routes, 54 such as multi domain (MD) formation, 20,24,30,31,39,40 coherent uniform rotation, isolated domain nucleation followed by domain wall depinning and rapid propagation, 17,49,51 or a sequential combination of these processes. However, a common characteristic of thin films and their magnetization reversal is that in order to minimize the magnetostatic energy, the magnetization tries to orient within the film plane, at least in the absence of large out-of-plane magnetocrystalline anisotropy 39 large out-of-plane magnetocrystalline anisotropy, it has been previously observed that it can be energetically favorable to form complex domains, such as stripe and bubble domains with a local magnetization component out-of-plane.…”

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

“…So little is known about the behavior of materials with high perpendicular anisotropy121314. A notable exception of materials with perpendicular anisotropy is the ferrimagnetic CoFeGd, which was studied in all-optical ultrafast switching triggered by a single laser pulse515.…”