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Roemer, Ryan

University of British Columbia

We present a systematic study of Fe₃GeTe₂(FGT), examining its electronic structure, magnetic properties, and evolution from monolayer to multilayer forms. Using molecular beam epitaxy, we achieve wafer-scale growth of high-quality, single-crystalline FGT films with controlled thickness from 1 to 10 quintuple layers (QL). Structural analysis via scanning transmission electron microscopy, X-ray diffraction, and crystal truncation rod techniques confirms excellent crystallinity and stoichiometry. Transport measurements reveal robust ferromagnetism across all thicknesses, with Curie temperatures rising from 75 K (1 QL) to over 175 K (10 QL). X-ray magnetic circular dichroism at 20 K reveals nearly quenched orbital contributions. Angle-resolved photoemission spectroscopy and density functional theory reveal the evolution of electronic bands and the role of interlayer coupling. Notably, the carrier density at the Curie temperature remains constant when normalized to layer number, suggesting a universal ferromagnetic transition mechanism. Stoner analysis shows 𝑰𝑫(EF) > 1 in all cases, indicating itinerant ferromagnetism. Fe II sites exhibit a monotonic increase in the Stoner criterion with thickness, while Fe I sites remain constant, supporting the view of FGT as a site-differentiated Hund's metal. Our demonstration of precise, scalable growth and comprehensive characterization establishes FGT as a promising platform for spintronic applications. Control over thickness enables systematic tuning of magnetic properties, while the observed correlation between carrier density and Curie temperature provides a quantitative framework for engineering room-temperature ferromagnetism in two-dimensional systems. These insights advance both fundamental understanding and practical strategies for manipulating magnetism in ultrathin van der Waals materials.

Text

2025-05-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/91233

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/