Fe-Intercalation Dominated Ferromagnetism of van der Waals Fe 3 GeTe 2 .

Fe 3 GeTe 2 have proven to be of greatly intrigue. However, the underlying mechanism behind the varying Curie temperature (T c ) values remains a puzzle. Here, we explored the atomic structure of Fe 3 GeTe 2 crystals exhibiting T c values of 160, 210, and 230 K. The elemental mapping reveals a Fe-intercalation on the interstitial sites within the van der Waals gap of the high- T c (210 and 230 K) samples, which are observed an exchange bias effect by electrical transport measurements, while Fe intercalation or the bias effect is absent in the low-T c (160 K) samples. First-principles calculations further suggest that the Fe-intercalation layer may be responsible for the local antiferromagnetic coupling that gives rise to the exchange bias effect, and that the interlayer exchange paths greatly contributes to the enhancement of T c . This discovery of the Fe-intercalation layer elucidates the mechanism behind the hidden antiferromagnetic ordering that underlies the enhancement of T c in Fe 3 GeTe 2 . This article is protected by copyright. All rights reserved.