Decomposition-Induced Room-Temperature Magnetism of the Na-Intercalated Layered Ferromagnet Fe<sub>3-<i>x</i></sub>GeTe<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 31251638.
- Also identified by DOI 10.1021/acs.nanolett.9b01287.
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Abstract
The creation of 2D van der Waals materials with ferromagnetism above room temperature is an essential goal toward their practical utilization in spin-based applications. Recent studies suggest that intercalating lithium in exfoliated flakes of the ferromagnet Fe<sub>3-<i>x</i></sub>GeTe<sub>2</sub> induces a nonzero magnetization at <i>T</i> ∼ 300 K. However, the nanoscale nature of such experiments precludes precise observations of structural and chemical changes upon intercalation. Here, we report the preparation of sodium-intercalated NaFe<sub>2.78</sub>GeTe<sub>2</sub> as well as the investigation into its structure and magnetic properties. Sodium readily intercalates into the van der Waals gap, as revealed by synchrotron X-ray diffraction. Concurrently, the Fe<sub>2.78</sub>GeTe<sub>2</sub> layer becomes heavily charge doped and strained via chemical pressure, yet retains its structure and ferromagnetic transition temperature of ∼140 K. However, we observe the presence of a ferromagnetic amorphous iron germanide impurity over a wide range of synthetic conditions, leading to room-temperature magnetization. This work highlights the importance of strain and electronic control for manipulating the Curie temperature in 2D ferromagnets, while emphasizing the need for careful chemical analysis when exploring phenomena in exfoliated layers.