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DOE OSTI · 3452361

Mesoscale Magnetostructural Phase Separation in Fe‐deficient Fe 5 GeTe 2

Ni, Haoyang [Univ. of Illinois at Urbana-Champaign, IL (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)]·Hoglund, Eric R. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)]·Hachtel, Jordan A. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)] (ORCID:0000000297280920)·Zuo, Jian‐Min [Univ. of Illinois at Urbana-Champaign, IL (United States); Monash Univ., Melbourne, VIC (Australia)]·Wu, Lijun [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:000000028443250X)·Zhu, Yimei [Brookhaven National Laboratory (BNL), Upton, NY (United States)]·May, Andrew F. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000307778539)·Chi, Miaofang [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)] (ORCID:0000000307641567)
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Abstract

Two-dimensional van der Waals ferromagnet Fe 5-x GeTe 2 (F5GT) is promising for spintronic applications due to its high Curie temperature, layered structure, and ability to host complex magnetic textures. However, the origin of its sample-dependent magnetic anisotropy remains unclear, hindering control of its magnetic behavior. Here, we use spatially resolved cryogenic scanning transmission electron microscopy (STEM) to correlatively map magnetism, lattice structure, and chemistry across atomic-to-micron scales. We reveal that only mesoscale, not nanoscale, inclusions of a Fe-deficient secondary phase significantly modify magnetic behavior, establishing a previously unrecognized critical length scale. This phase separation, induced by quenching, leads to in-plane magnetic anisotropy, while slow cooling confines separation to a few nanometers and preserves out-of-plane anisotropy. These findings reconcile prior inconsistencies and establish a predictive framework for tuning magnetism in F5GT through thermal processing, with broader implications for controlling anisotropy in other two-dimensional magnetic materials.

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2D ferromagnets36 MATERIALS SCIENCE4D scanning transmission electron microscopyFe5GeTe2Lorentz 4D-STEMcryogenic STEM

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Ni, Haoyang [Univ. of Illinois at Urbana-Champaign, IL (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)], Hoglund, Eric R. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)], Hachtel, Jordan A. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)] (ORCID:0000000297280920), Zuo, Jian‐Min [Univ. of Illinois at Urbana-Champaign, IL (United States); Monash Univ., Melbourne, VIC (Australia)], Wu, Lijun [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:000000028443250X), Zhu, Yimei [Brookhaven National Laboratory (BNL), Upton, NY (United States)], May, Andrew F. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000307778539), Chi, Miaofang [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)] (ORCID:0000000307641567). 2025-12-26. Mesoscale Magnetostructural Phase Separation in Fe‐deficient Fe 5 GeTe 2. https://doi.org/10.1002/adma.202515150

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