PAPER / ARXIV:2609.11862
Tyler L. Werner (1), Jonathan T. Reichanadter (2 and 3), Xiang Chen (2 and 4), Pranab K. Nag (5 and 6), Luna Y. Liu (1), Yu-Tsun Shao (7 and 8), Hongrui Zhang (9), Mingyang Guo (10), Wenxin Li (1), Zhibo Kang (1), Han Wu (11 and 12), Makoto Hashimoto (13), Donghui Lu (13), Turgut Yilmaz (14), Elio Vescovo (14), Sung-Kwan Mo (15), Barat Achinuq (15), Alexei Fedorov (15), Jacob C. Ruff (16), Ming Yi (11 and 12), Qiong Ma (10 and 17), David A. Muller (7 and 18), Eduardo H. da Silva Neto (1, 5 and 6), Robert J. Birgeneau (2 and 4), Jeffrey B. Neaton (2 and 19), Yu He (1) ((1) Department of Applied Physics, Yale University, New Haven, USA, (2) Department of Physics, University of California, Berkeley, Berkeley, USA, (3) Department of Electrical Engineering and Computer Science, University of California, Berkeley, Berkeley, USA, (4) Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA, (5) Department of Physics, Yale University, New Haven, USA, (6) Energy Sciences Institute, Yale University, West Haven, USA, (7) School of Applied and Engineering Physics, Cornell University, Ithaca, USA, (8) Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, USA, (9) Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, USA, (10) Department of Physics, Boston College, Chestnut Hill, USA, (11) Department of Physics and Astronomy, Rice University, Houston, USA, (12) Rice Center for Quantum Materials, Rice University, Houston, USA, (13) Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, USA, (14) National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, USA, (15) Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, USA, (16) Cornell High Energy Synchrotron Source, Cornell University, Ithaca, USA, (17) Schiller Institute for Integrated Science and Society, Boston College, Chestnut Hill, USA, (18) Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, USA, (19) Kavli Energy Nanosciences Institute at Berkeley, Berkeley, USA)
RESUMO
The discovery of high-temperature ferromagnetism in the metallic van der Waals (vdW) system Fe$_N$GeTe$_2$ has brought two-dimensional (2D) magnets into technologically relevant temperature scales. Specifically at N = 5, dilution of magnetic moments by nickel substitution counterintuitively achieves a record high Curie temperature of 478~K. Unraveling the origin of this nickel-substitution-induced enhancement is complicated by the compound's structural complexity, coexistent itinerant and local magnetic contributions, and mesoscopic compositional domains. Through coordinated structural and electronic characterization, we identify that the high-T$_C$ magnetic phase arises from a strain-stabilized Fe$_6$GeTe$_2$ nano-precipitate. Combining first-principles calculations and spin- and angle-resolved photoemission spectroscopy (ARPES), we uncover a site-specific electronic landscape in which interior iron atoms primarily host localized moments while the outer iron atoms neighboring the tellurium layers produce spin-polarized itinerant carriers that cross the vdW gap. The large energy cost associated with homogeneous nickel substitution is found to favor the spontaneous precipitation of the crystallographically and electronically ``clean'' high-T$_C$ phase. Finally, we compare metal-rich vdW magnets with binary magnetic alloys, and discuss the unifying roles of nano-precipitates in stabilizing otherwise unattainable bulk phases. Our work provides mechanistic insights into the record-high T$_C$ ferromagnetism in (Fe,Ni)$_{5+\delta}$GeTe$_2$, establishing a rigorous foundation for the atomic engineering of vdW magnetic metals informed by direct electronic signatures.
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