Optical Markers of Magnetic Phase Transition in CrSBr

Two-dimensional (2D) magnetic semiconductors give the opportunity to take advantage of the electron charge and the electron spin at the same time, which gives the possibility of broadening modern semiconductor technology and spintronic devices [1] and can greatly expand the applications of ferromagnets (FM) in other devices such as transformers, electromagnets, high-density storage, and magnetic random access memory [2].<br/>Here, we present the role of the interlayer magnetic ordering of CrSBr in the framework of <i>ab initio</i> calculations and by using optical spectroscopy techniques. These combined studies allow us to unambiguously determine the nature of the optical transitions. In particular, photoreflectance measurements, sensitive to the direct transitions, have been carried out for the first time. We have demonstrated that optically induced band-to-band transitions visible in optical measurement are remarkably well assigned to the band structure by the momentum matrix elements and energy differences for the magnetic ground state (A-AFM). In addition, our study reveals significant differences in electronic properties for two different interlayer magnetic phases. When the magnetic ordering of A-AFM to FM is changed, the crucial modification of the band structure reflected in the direct-to-indirect band gap transition and the significant splitting of the conduction bands along the Γ-Z direction are obtained. In addition, Raman measurements demonstrate a splitting between the in-plane modes B²_2g/B²_3g which is temperature dependent and can be assigned to different interlayer magnetic states, corroborated by the DFT+U study. Moreover, the B²_2g mode has not been experimentally observed before. Finally, our results point out the origin of interlayer magnetism, which can be attributed to electronic rather than structural properties. Our results reveal a new approach for tuning the optical and electronic properties of van der Waals magnets by controlling the interlayer magnetic ordering in adjacent layers [3].<br/><br/>[1] D. D. Awschalom and M. E. Flatté, Nature Physics, 2007, <b>3</b>, 153<br/>[2] S. Chen, <i>et al.</i> J. Phys. Chem. C, 2019, <b>123</b>, 17987<br/>[3] W. M. Linhart <i>et al.</i> J. Phys. Chem. C, 2023, <b>11</b>, 8423<br/><br/>This work was carried out under the grant of the National Science Centre, Poland (Grant No. 2019/35/B/ST5/02819). M.B. acknowledges support from the University of Warsaw within the project “Excellence Initiative-Research University” program.