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Te
Wang, Y.*; 梶原 駿*; 松岡 秀樹*; Saika, B. K.*; 山神 光平*; 竹田 幸治; 和達 大樹*; 石坂 香子*; 岩佐 義宏*; 中野 匡規*
Nano Letters, 22(24), p.9964 - 9971, 2022/12
被引用回数：9 パーセンタイル：83.82(Chemistry, Multidisciplinary)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 CrTe. We fabricated CrTe thin films by molecular-beam epitaxy and found that CrTe could host two distinct ferromagnetic phases characterized with different Curie temperatures (
). One is the bulk-like high- phase showing room-temperature ferromagnetism, which is consistent with previous studies. The other is the metastable low- phase with 
160 K, which exhibits a layer-number-independent down to the 2D limit in marked contrast with the conventional high- 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.
松岡 秀樹*; Barnes, S. E.*; 家田 淳一; 前川 禎通; Bahramy, M. S.*; Saika, B. K.*; 竹田 幸治; 和達 大樹*; Wang, Y.*; 吉田 訓*; et al.
Nano Letters, 21(4), p.1807 - 1814, 2021/02
被引用回数：13 パーセンタイル：77.64(Chemistry, Multidisciplinary)Magnetocrystalline anisotropy, a key ingredient for establishing long-range order in a magnetic material down to the two-dimensional (2D) limit, is generally associated with spin-orbit interaction (SOI) involving a finite orbital angular momentum. Here we report strong out-of-plane magnetic anisotropy without orbital angular momentum, emerging at the interface between two different van der Waals (vdW) materials, an archetypal metallic vdW material NbSe
possessing Zeeman-type SOI and an isotropic vdW ferromagnet V
Se
. We found that the Zeeman SOI in NbSe induces robust out-of-plane magnetic anisotropy in V
Se
down to the 2D limit with a more than 2-fold enhancement of the transition temperature. We propose a simple model that takes into account the energy gain in NbSe in contact with a ferromagnet, which naturally explains our observations. Our results demonstrate a conceptually new magnetic proximity effect at the vdW interface, expanding the horizons of emergent phenomena achievable in vdW heterostructures.
Se epitaxial thin films中野 匡規*; Wang, Y.*; 吉田 訓*; 松岡 秀樹*; 真島 裕貴*; 池田 啓祐*; 平田 靖透*; 竹田 幸治; 和達 大樹*; 小濱 芳允*; et al.
Nano Letters, 19(12), p.8806 - 8810, 2019/12
被引用回数：56 パーセンタイル：92.05(Chemistry, Multidisciplinary)The discoveries of intrinsic ferromagnetism in atomically thin van der Waals crystals have opened a new research field enabling fundamental studies on magnetism at two-dimensional (2D) limit as well as development of magnetic van der Waals heterostructures. Here we demonstrate that VSe epitaxial thin films grown by molecular-beam epitaxy exhibit emergent 2D ferromagnetism with intrinsic spin polarization of the V 3d electrons although the bulk counterpart is originally antiferromagnetic. Moreover, thickness-dependence measurements reveal that this newly developed 2D ferromagnet could be classified as an itinerant 2D Heisenberg ferromagnet with weak magnetic anisotropy.
