Magnetooptical investigations on thin ferromagnetic films

Various applications of the Faraday and Kerr effects for the investigation of domain structures and reversal mechanisms in thin ferromagnetic films are reviewed. Different optical arrangements for the observation of domains are described and compared. Using magnetooptic microscopy domains and wall structures can be observed with a resolution of 1 μm. Magnetization structures give rise to diffraction phenomena, which are revealed as Fresnel fringes, Fraunhofer patterns, and dark field pictures. Applications of these phenomena and the consequences for the resolution of magneto-optic microscopy are discussed. Various kinds of reversal processes by wall motion or rotation, respectively, can be distinguished from each other by measuring the light intensity in two settings of the analyzer and by a dark field method. These reversal mechanisms can be identified even in case of fast switching when direct observations are not possible. Since the applications of magnetooptics are not restricted by any temperature limit, they are especially suited for the investigation of temperature dependent phenomena, e.g., the Barkhausen effect and the magnetic aftereffect. A picture of a domain structure in a gadolinium film at 80°K is shown.