Design of TbxCo100-x for All Optical Switching of Magnetization

Abstract

Observation of All-Optical Switching (AOS) of magnetization in ferrimagnetic GdFeCo alloys, using ultrashort circularly polarized laser pulses [1], triggered a renewed interest in ferrimagnetic rare Earth-transition metal (RE-TM) alloys [1-5]. Tb-containing ferrimagnetic alloys exhibit all-optical helicity-dependent switching (AO-HDS), and have strong perpendicular magnetic anisotropy, a result of a high spin-orbit coupling in Tb [6]. In this work we study the magnetic properties and AOS performance of amorphous TbCo alloys, prepared by a DC magnetron sputtering (for more details see [7]). We measured μ0Hc using polar magneto-optical Kerr effect (MOKE), and investigated the AOS behaviour using a pump-probe based static magneto-optical imaging setup. We show that AO-HDS is possible in TbxCo100−x for certain compositions (x=24-30 at.%) and thicknesses (Fig. 1), if the laser pulse parameters such as pump fluence, are optimized, and the number of pulses in one burst is at least 50-100. Samples with the compositions out of this range show only helicity-independent thermal demagnetization. We also performed ab initio calculations of the inverse Faraday effect to explain the cumulative nature of the multi-shot AO-HDS switching. It is triggered by circularly polarized laser light, inducing a helicity dependent magnetic moment in the Co atoms of the alloys (Fig. 2). This study shows that ferrimagnetic TbCo films can exhibit AO-HDS in a certain compositional range and laser pulse parameters, with a minimal amount of shots.