Fermiology Underpinning Enhanced Magnetic Ordering in Cr2Ge2Te6 van der Waals Magnets

The recent discovery of long-range magnetic order in van der Waals layered materials, persisting to the few-layer limit, has provided a tuneable platform for the engineering of novel magnetic structures and devices. Cr₂Ge₂Te₆ is such a material [1]. It is known to be a ferromagnetic semiconductor with a <i>T_C</i> of approximately 63 K in the bulk crystal. The <i>T_C</i> reduces with sample thickness but remains finite down to the bilayer limit. Electrostatic gating studies on Cr₂Ge₂Te₆ have demonstrated how the induced carrier doping can drive a marked increase in <i>T</i>_C, as well as switching the magnetic anisotropy [2]. Here we show how features of the electronic structure, extracted from angle-resolved photoemission spectroscopy (ARPES), can be used to provide a direct probe of orbital-specific energy gains underpinning the magnetic ordering. We perform measurements as a function of temperature and alkali surface deposition, an analogue to electrostatic-gating, to simultaneously investigate the effects of electron doping on the near-surface band-structure, and to extract the <i>T</i>_C of the surface region. We find how <i>T</i>_Cis increased in the electron-doped surface as compared to the bulk system, and image the population of the nominally unoccupied conduction band that underpins these changes in magnetic ordering.<br/><br/><br/><b>References</b><br/>[1] Cheng Gong, <i>et al</i>, Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. <i>Nature</i>, 546(7657):265–269, (2017).<br/>[2] Verzhbitskiy, <i>et al.</i> Controlling the magnetic anisotropy in Cr₂Ge₂Te₆ by electrostatic gating. <i>Nat Electron</i> 3<b>, </b>460–465 (2020).<br/>[3] Watson, <i>et al</i>, Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe_3,<i>Phys Rev B </i>101, (2020)