Mechanism For All-Optical Magnetization Switching

Resonant absorption of a photon by bound electrons in a solid can promote an electron to another orbital state or transfer it to a neighboring atomic site. Such a transition in a magnetically ordered material could affect the magnetic order. While this process is an obvious road map for optical control of magnetization, experimental demonstration of such a process remains challenging. Exciting a significant fraction of magnetic ions requires a very intense incoming light beam, as orbital resonances are often weak compared to above-band-gap excitations. In the latter case, a sizeable reduction of the magnetization occurs as the absorbed energy increases the spin temperature, masking the non-thermal optical effects.

optical magnetization switching
Schematic visualization of microscopic magnetization dynamics. Here, only magnetic ions with tetrahedral coordination are shown. Prior to excitation, all these moments (Mtetra) are pointing along the equilibrium orientation direction (a). Optical excitation changes the orbital state of the Co ion, which results in a different single-ion anisotropy easy-magnetization axis. This induces the reorientation of spins of the nearest Fe moments (b). The reorientation cascade, shown as a dashed orange circle, propagates away from the initially excited Co ion affecting Fe ions located further away at later times as shown on panels (c) and (d).

Here, using ultrafast X-ray spectroscopy, this work is able to resolve changes in the magnetization state induced by resonant absorption of infrared photons in Co-doped yttrium iron garnet, with negligible thermal effects. This work finds that the optical excitation of the Co ions affects the two distinct magnetic Fe sublattices differently, resulting in a transient non-collinear magnetic state. The present results indicate that the all-optical magnetization switching (AOS) most likely occurs due to the creation of a transient, non-collinear magnetic state followed by coherent spin rotations of the Fe moments.


Dr Urs Staub
Microscopy and Magnetism Group
Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
Telephone: +41 56 310 44 94

Original Publication

Transient non-collinear magnetic state for all-optical magnetization switching
S. Parchenko, A. Frej, H. Ueda, R. Carley, L. Mercadier, N. Gerasimova, G. Mercurio, J. Schlappa, A.  Yaroslavtsev, N. Agarwal, R. Gort, A. Scherz, A. Zvezdin, A. Stupakiewicz and U. Staub
Advanced Science 10, 2302550 (2023)
DOI: 10.1002/advs.202302550