Depth-Dependent Magnetic Properties in the Ferromagnetic van der Waals Semiconductor VI₃

Two-dimensional van der Waals (vdW) magnetic semiconductors display emergent chemical and physical properties arising from both intra-layer and inter-layer interaction, both providing a versatile toolkit for studying quantum phenomena in heterostructures and few layers systems, as well as holding promise for novel quantum spintronic functionalities [1,2].<br/><br/>Among 3d transition-metal vdW, VI₃ has recently attracted significant attention, as due to a) the presence of both structural and magnetic transitions as a function of temperature, suggesting a relevant role of magnetoelastic interactions and b) the interplay of dimensionality with relevant interactions, such as spin–orbit coupling (SOC), where a crossover of 3D vs. 2D electronic properties is expected [1]. However, detailed experimental information on ground state electronic properties as well as on spin/orbital degrees of freedom are still lacking, mainly due to its extreme air sensitivity and challenging chemical environment.<br/><br/>Here we present chemical and layer sensitive X-ray electron spectroscopies results supported by model calculation, where we report via PhotoElectron Spectroscopy (RESPES and ARPES) a complete characterization of the electronic ground states of VI₃, showing that orbital filling drives the stabilization of a quasi-Mott insulating state at the surface, with strong influence of dimensionality effects [3]. Moreover, Temperature-dependent X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) experiments clearly reveal a reduced dimensionality of magnetic order, due to electronic correlations, providing evidence of (a) an unquenched orbital magnetic moment (up to 0.66(7) μB/V atom) in the ferromagnetic state and (b) an instability of the orbital moment in the proximity of the spin reorientation transition [4,5].<br/><br/>Our results have direct implications in band engineering and layer-dependent properties of two-dimensional systems, suggesting VI₃ as a relevant candidate for the study of orbital quantum effects in spintronics interface and heterostructures.<br/><br/>References<br/><br/>[1] M. Gibertini, M. Koperski, A. F. Morpurgo, and K. S. Novoselov, Nature Nanotechnology 2019 14:5 14, 408 (2019).<br/>[2] B. Huang, G. Clark, E. Navarro-Moratalla, D. R. Klein, R. Cheng, K. L. Seyler, Di. Zhong, E. Schmidgall, M. A. McGuire, D. H. Cobden, W. Yao, D. Xiao, P. Jarillo-Herrero, and X. Xu, Nature 546, 270 (2017).<br/>[3] A. De Vita, T.T.P. Nguyen, R. Sant, G.M. Pierantozzi, D. Amoroso, C. Bigi, V. Polewczyk, G. Vinai, L.T. Nguyen, T. Kong, J. Fujii, I. Vobornik, N.B. Brookes, G. Rossi, R.J. Cava, F. Mazzola, K. Yamauchi, S. Picozzi and G. Panaccione, Nano Letters 2022, 22, 17, 7034—7041.<br/>[4] A. De Vita, R. Sant, V. Polewczyk, G. van der Laan, N.B. Brookes, T. Kong, R.J. Cava, G. Rossi, G. Vinai and G. Panaccione, Nano Letters 2024, 24, 5, 1487–1493.<br/>[5] R. Sant, A. De Vita, V. Polewczyk, G.M. Pierantozzi, F. Mazzola, G. Vinai, G. van der Laan, G. Panaccione and N.B. Brookes, 2023 J. Phys.: Condens. Matter 35 405601