All-Optical Magnetization Switching on Multi Level GdFeCo Magnetic Double Layered Film

Abstract

All-Optical magnetization Switching (AOS) is triggered by ultra-short light-matter interaction that is much shorter time scale than conventional magnetic field driven magnetic recording method[1]. The switching “on” and “off’ strongly depends on absorbed energy and its fluence. In addition, the switching mechanism is differently based on sub-ps energy dissipation process in material[2]. So we can expect considerable rapid magnetic recording with AOS. Furthermore we can anticipate that AOS allows as a new type of multi-value magnetic recording without external magnetic field. In this report we irradiated a single femtosecond laser pulse to the double layered film and observed the magneto-optical image of the created magnetic domains. We designed the film structure which have GdFeCo double layer with dielectric interlayer: SiN (60 nm) / Layer I: Gd 27 Fe 63.9 Co 9.1 (10 nm) / SiN (5 nm) / Layer II :Gd 22 Fe 68.2 Co 9 . 8 (10 nm) / SiN (5 nm) / A1Ti (10 nm) / glass sub. Dielectric SiN interlayer decouple magnetic exchange interaction and electric conduction between two metallic GdFeCo magnetic layers. This double layered film shows 4 level magnetization state and Faraday rotation signals. We found that the different state transition diagram in double magnetic layer can realise compared with magnetic field driven magnetic transition diagram. After irradiation of single femtosecond laser pulse, just the magnetization of Layer I reversed in spite of it have much higher coercivity than Layer II. In addition, we irradiated higher intense laser pulse to the sample. Fig. 1 shows the magneto-optical image of the created magnetic domain and area profile of the image. This result shows three magnetic state was simultaneously created following Gaussian intensity profile of irradiated laser pulse.