CrSBr is an an antiferromagnetic semiconductor belonging to the family of exfoliable van der Waals system, “re-discovered” around 2020 [1]. In comparison to the famous van der Waals system CrI₃, CrSBr has higher Néel temperature (132K) and it is air-stable. Moreover, the easy-axis for CrSBr is in-plane while it’s out-of-plane for CrI₃. In CrSBr, Cr ions are ferromagnetically coupled within the plane with interplane antiferromagnetic coupling. The spins can be flipped to a ferromagnetic alignment with moderate fields (below 1T for the bulk material along the easy axis) [1]. In addition, strain can also change the antiferro to ferromagnetic coupling [2]. Muon spectroscopy has shown an additional phase transition at low temperatures, associated to a spin-freezing of the system [3]. The transport in the plane was shown to be extremely anisotropic, hinting to quasi-1D behavior [4]. More recently it was shown a high magneto-optical coupling in this system [5].

Motivated by the interesting results from Refs 1-4 we have used x-ray spectroscopy to probe the magnetic and electronic properties of CrSBr in bulk. X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD) at the Cr L_3,2-edges was measured for different crystal orientations and as function of temperature. XLD is sensitive to charge anisotropy around Cr. This anisotropy can come either from magnetism through spin-orbit coupling, or from the ligand field. In the first case the technique is often called X-ray magnetic linear dichroism (XMLD). XMLD is widely used to characterize antiferromagnetic systems, since XMCD is zero for antiferromagnets. After we performed our measurements, a work was published showing XMLD and XMCD measurements on CrSBr [6]. Our measured spectra agree with those published in [6]. To understand our data, we performed ab-initio XMLD and XMCD simulations. Our simulations agree very well with the data measured at low temperature (below T_N). However, as also observed in [6] the XLD does not go to zero above T_N. Ref [6] attributes that to a dichroism remaining from ligand field (natural linear dichroism). However, our ab-initio simulations do not reproduce this large anisotropic contribution remaining up to 300K. In this talk I will present our experimental and theoretical results, discussing what we can learn from the simulations and which points are still open.

References
[1] E. J. Telford et al., Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der Waals Semiconductor CrSBr, Advanced Materials 32, 2003240 (2020).
[2] J. Cenker et al., Reversible strain-induced magnetic phase transition in a van der Waals magnet, Nature Nanotechnology 17, 256 (2022).
[3] S. A. López-Paz, Z. Guguchia, V. Y. Pomjakushin, C. Witteveen, A. Cervellino, H. Luetkens, N. Casati, A. F. Morpurgo, and F. O. von Rohr, Dynamic magnetic crossover at the origin of the hidden-order in van der Waals antiferromagnet CrSBr, Nature Communications 13, 4745 (2022).
[4] F. Wu, I. Gutierrez-Lezama, S. A. Lopez-Paz, M. Gibertini, K. Watanabe, T. Taniguchi, F. O. von Rohr, N. Ubrig, and A. F. Morpurgo, Quasi-1D Electronic Transport in a 2D Magnetic Semiconductor, Advanced Materials 34, 2109759 (2022).
[5] F. Dirnberger et al., Magneto-optics in a van der Waals magnet tuned by self-hybridized polaritons, Nature 620, 533 (2023).
[6] F. Pei et al., Surface‐Sensitive Detection of Magnetic Phase Transition in Van Der Waals Magnet CrSBr, Adv. Funct. Mater. (2024).