Tunable magnetic properties in van der Waals crystals (Fe1−xCox)5GeTe2

Abstract

We report the doping effects of cobalt on van der Waals (vdW) magnet Fe5GeTe2. A series of (Fe1−xCox)5GeTe2 (0 ≤ x ≤ 0.44) single crystals have been grown, and their structural, magnetic, and transport properties are investigated. For x = 0.20, the Curie temperature TC increases from 276 K to 337 K. Moreover, the magnetic easy axis is reoriented to the ab-plane from the c-axis in undoped Fe5GeTe2 with largely enhanced magnetic anisotropy. A complex magnetic phase diagram is identified on the higher doping side. The x = 0.44 crystal first orders ferromagnetically at TC = 363 K and then undergoes an antiferromagnetic (AFM) transition at TN = 335 K. Furthermore, magnetic-field-induced spin-flop transitions are observed for the AFM ground state. Our work reveals (Fe1−xCox)5GeTe2 as promising candidates for developing spin-related applications and proposes a method to engineer the magnetic properties of the vdW magnet.

Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetism

“…The very recent calculations indicate that monolayer formation energy of Fe 5 GeTe 2 lies inside the energy range of other 2D materials 55 , and the synthesis of the monolayer is therefore highly expected. Moreover, considering the tunable T C which can even to be ~ 350 K 20,21,56 , the investigation on the precise magnetic structure of Fe 5 GeTe 2 would find extraordinary opportunities for applications in next-generation spintronic devices.…”

“…The tremendous efforts in perusing high T C magnets more recently led to the discovery of a T C of ~ 130-230 K in the bulk quasi-2D vdW Fe 3-x GeTe 2 , which can even be enhanced up to room temperature 18 . Interestingly, similar as Fe 3-x GeTe 2 , bulk Fe 5-x GeTe 2 shows a tunable T C ranging from ~ 270 to ~ 363 K by controlling the Fe deficiency content x or by substituting Co for Fe, suggesting the detrimental role of Fe in the magnetic exchange 20,21,56 . A reversible magnetoelastic coupled first-order transition near 100 K was detected by neutron powder diffraction 20 .…”

Large-scale epitaxy of two-dimensional van der Waals room-temperature ferromagnet Fe5GeTe2

“…Fe3GeTe2 exhibits a TC of 230 K 14,15 in bulk form and 130 K 5 for a single layer. In these systems, the TC can be tuned via the use of extrinsic mechanisms such as ionic gating 16 , doping 17 , ion implantation 18 , proximity to topological insulators 19 , and patterning methods 20 . Metastable states can be stabilized via temperature quenching and temperature-cycles 21 .…”

DyOCl: a rare-earth based two-dimensional van der Waals material with strong magnetic anisotropy

“…When higher magnetic field of 50 kOe was applied, a four-fold symmetric pattern arises in the in-plane magnetization with maximum along both a-and b-axis, minimum along [110]-axis. The above results demonstrate the large in-plane magnetic anisotropy of DyOCl, which is quite different from 2D transitional metal based magnetic vdW magnets with almost negligible in-plane anisotropy such as CrCl 3 and Co-doped Fe-Ge-Te series [38][39][40][41]. Therefore, although DyOCl favors an in-plane magnetization, it actually exhibits an Ising-like uniaxial magnetocrystalline anisotropy which enables the opening a spin-wave gap to resist thermal fluctuations.…”