Layer-Number-Independent Two-Dimensional Ferromagnetism in Cr<sub>3</sub>Te<sub>4</sub>.

Wang, Yue; Kajihara, Shun; Matsuoka, Hideki; Saika, Bruno Kenichi; Yamagami, Kohei; Takeda, Yukiharu; Wadati, Hiroki; Ishizaka, Kyoko et al. · Nano Lett · 2022

basic_science · Level V

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Abstract

In a conventional magnetic material, a long-range magnetic order develops in three dimensions, and reducing a layer number weakens its magnetism. Here we demonstrate anomalous layer-number-independent ferromagnetism down to the two-dimensional (2D) limit in a metastable phase of Cr<sub>3</sub>Te<sub>4</sub>. We fabricated Cr<sub>3</sub>Te<sub>4</sub> thin films by molecular-beam epitaxy and found that Cr<sub>3</sub>Te<sub>4</sub> could host two distinct ferromagnetic phases characterized with different Curie temperatures (<i>T</i><sub>C</sub>). One is the bulk-like "high-<i>T</i><sub>C</sub> phase" showing room-temperature ferromagnetism, which is consistent with previous studies. The other is the metastable "low-<i>T</i><sub>C</sub> phase" with <i>T</i><sub>C</sub> ≈ 160 K, which exhibits a layer-number-independent <i>T</i><sub>C</sub> down to the 2D limit in marked contrast with the conventional high-<i>T</i><sub>C</sub> phase, demonstrating a purely 2D nature of its ferromagnetism. Such significant differences between two distinct phases could be attributed to a small variation in the doping level, making this material attractive for future ultracompact spintronics applications with potential gate-tunable room-temperature 2D ferromagnetism.