Nearly room temperature ferromagnetism in a magnetic metal-rich van der Waals metal

Abstract

In spintronics, two-dimensional van der Waals crystals constitute a most promising material class for long-distance spin transport or effective spin manipulation at room temperature. To realize all-vdW-material–based spintronic devices, however, vdW materials with itinerant ferromagnetism at room temperature are needed for spin current generation and thereby serve as an effective spin source. We report theoretical design and experimental realization of a iron-based vdW material, Fe4GeTe2, showing a nearly room temperature ferromagnetic order, together with a large magnetization and high conductivity. These properties are well retained even in cleaved crystals down to seven layers, with notable improvement in perpendicular magnetic anisotropy. Our findings highlight Fe4GeTe2 and its nanometer-thick crystals as a promising candidate for spin source operation at nearly room temperature and hold promise to further increase Tc in vdW ferromagnets by theory-guided material discovery.

Van der Waals Multiferroic Tunnel Junctions

“…Supplementary Figure S1 shows the calculated spin-polarized band structure and density of states (DOS) of bulk FenGeTe2 which we find consistent with the previous results [25]. The calculated average magnetic moment on Fe atoms is 2.10 μB, 2.15 μB and 2.11 μB for n = 3, 4, 5 respectively, which are somewhat larger than the experimental values for Fe3GeTe2 (1.63 μB) [24], Fe4GeTe2 (1.8 μB) [25] and Fe5GeTe2 (2.0 μB) [27]. This discrepancy may partly be attributed to the imperfect stoichiometry in the experimentally prepared samples.…”

“…Specifically, it has been reported that the graphite/CrI3/graphite vdW tunnel junctions exhibit a huge magnetoresistance effect over thousands of percent at low temperature. [20] [21] [22] [23] Among known 2D ferromagnetic vdW metals, FenGeTe2 (n = 3, 4, 5) compounds [24] [25] [26] [27] [28] exhibit high Curie temperature TC (about 220 K for Fe3GeTe2, 280 K for Fe4GeTe2, and over 300 K for Fe5GeTe2) and thus are promising for spintronic applications.…”

“…Here, for simplicity, we use the theoretically predicted crystal structure of Fe5GeTe2 that belongs to the P3m1 space group and has A-A stacking. [25] The in-plane lattice constants of FenGeTe2 and α-In2Se3 have a mismatch of less than 1%, which allows using an (1×1) in-plane unit cell to model FemGeTe2/α-In2Se3/FenGeTe2…”

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

“…In principle, the discovery of atomically thin materials with intrinsic ferromagnetism and high-magnetic ordering temperature could open up opportunities to realize spintronic devices, such as molecular quantum devices and high-density ultrathin storage devices. Indeed, the recent groundbreaking experimental observations of the intrinsic magnetism in atomically thin FePS 3 , CrI 3 , Cr 2 Ge 2 Te 6 , and Fe 3 GeTe 2 [5][6][7][8][9][10][11] have pushed this class of materials to be promising candidates for possible applications in spintronic technology, as they can serve as building blocks for magnetic vdW heterostructures.…”

Itinerant ferromagnetism in van der Waals Fe5−xGeTe2 crystals above room temperature

“…Very recently, vdW Fe 4 GeTe 2 and Fe 5−x GeTe 2 phases have been synthesized displaying intrinsic ferromagnetism. Due, in part, to higher Fe concentrations in such systems, they exhibit an enhanced Curie temperature near room temperature (270-310 K) and a larger saturation magnetization (500-640 emu/cm 3 ) [28][29][30][31]. Additionally, Fe 5−x GeTe 2 single crystals show very complex magnetic behavior because of tunable iron content and iron vacancies.…”