Resonant Faraday effect using high-order harmonics for the investigation of ultrafast demagnetization

Carla Alves (1) , Guillaume Lambert (1) , Victor Malka (1) , Michel Hehn (2) , Grégory Malinowski (2) , Marcel Hennes (3) , Valentin Chardonnet (3) , Emmanuelle Jal (3) , Jan Lüning (4) , Boris Vodungbo (3)

1 LOA - Laboratoire d'optique appliquée
2 IJL - Institut Jean Lamour
3 LCPMR - Laboratoire de Chimie Physique - Matière et Rayonnement
4 LCPMR - Laboratoire de Chimie Physique - Matière et Rayonnement

During the past few years high-order harmonic generation (HHG) has opened up the field of ultrafast spectroscopy to an ever larger community by providing a table-top and affordable femtosecond extreme ultraviolet (EUV) and soft-x-ray source. In particular, the field of femtomagnetism has largely benefited from the development of these sources. However, the use of x-ray magnetic circular dichroism (XMCD) as a probe of magnetization, the most versatile and reliable one, has been constrained by the lack of polarization control at HHG sources, so studies have relied on more specific magneto-optical effects. Even the recent developments on the generation of elliptically polarized harmonics have only resulted in a few time-resolved experiments relying on this powerful technique since they add complexity to already-difficult measurements. In this article we show how to easily probe magnetization dynamics with linearly polarized EUV or soft-x-ray light with a versatility similar to XMCD by exploiting the Faraday effect. Static and time-resolved measurements of the Faraday effect are presented around the Co M edges. Using simple theoretical considerations, we show how to retrieve the samples magnetization dynamics from the Faraday rotation and ellipticity transients. Ultrafast demagnetization dynamics of a few nanometers in Co-based samples are measured with this method in out-of-plane as well as in-plane magnetization configurations, showing its great potential for the study of femtomagnetism.

Domains: Physics [physics]; Condensed Matter [cond-mat]; Physics [physics]; Condensed Matter [cond-mat]; Materials Science [cond-mat.mtrl-sci]

Carla Alves, Guillaume Lambert, Victor Malka, Michel Hehn, Grégory Malinowski, et al.. Resonant Faraday effect using high-order harmonics for the investigation of ultrafast demagnetization. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2019, 100 (14), ⟨10.1103/PhysRevB.100.144421⟩. ⟨hal-02337593⟩