Magnetic properties of intercalated quasi-2D Fe3-xGeTe2 van der Waals magnet

Abstract

Among several well-known transition metal-based compounds, cleavable van der Waals (vdW) Fe3-xGeTe2 (FGT) magnet is a strong candidate for use in two-dimensional (2D) magnetic devices due to its strong perpendicular magnetic anisotropy, sizeable Curie temperature (TC ~154 K), and versatile magnetic character that is retained in the low-dimensional limit. While the TC remains far too low for practical applications, there has been a successful push toward improving it via external driving forces such as pressure, irradiation, and doping. Here we present experimental evidence of a room temperature (RT) ferromagnetic phase induced by the electrochemical intercalation of common tetrabutylammonium cations (TBA+) into quasi-2D FGT. We obtained Curie temperatures as high as 350 K with chemical and physical stability of the intercalated compound. The temperature-dependent Raman measurements, in combination with vdW-corrected ab initio calculations, suggest that charge transfer (electron doping) upon intercalation could lead to the observation of RT ferromagnetism. This work demonstrates that molecular intercalation is a viable route in realizing high-temperature vdW magnets in an inexpensive and reliable manner, and has the potential to be extended to bilayer and few-layer vdW magnets.

Writing and Detecting Topological Charges in Exfoliated Fe5–xGeTe2

“…We found that it is quite difficult to align the field very carefully within the ab -plane (i.e., with a misalignment inferior to Δ θ ≈ 0.05°) and in this way detect ρ xy u,T (μ 0 H ) = 0 μΩ cm. Our micromagnetic simulations ,, mimicking an exfoliated sample (Figure S8) yield a topological charge density as a function of the interlayer magnetic field which displays a striking resemblance with the topological Hall response shown in Figure . The Hall resistance R xy is proportional to the topological number N Sk via R x y ∝ ∫ − y 0 y 0 ∫ − x 0 x 0 N S k false( x − x ′ , y − y ′ false) d x ′ d y ′ , which is related to the emergent field created by the spin textures via B em ∝ N Sk ê z .…”

“…We found that it is quite difficult to align the field very carefully within the ab-plane (i.e., with a misalignment inferior to Δθ ≈ 0.05°) and in this way detect ρ xy u,T (μ 0 H) = 0 μΩ cm. Our micromagnetic simulations 36,56,57 mimicking an exfoliated sample (Figure S8) yield a topological charge density as a function of the interlayer magnetic field which displays a striking resemblance with the topological Hall response shown in , 58 which is related to the emergent field created by the spin textures via B em ∝ N Sk eẑ. 59 Therefore, the topological Hall resistance is directly proportional to the emergent field induced by the spin textures and associated topological charge density due to the presence of skyrmions and merons.…”

“…The numerical simulations were performed using the Mumax3 solver, which allowed larger simulation sizes relative to atomistic spin dynamics. ,− ,− Regions of in-plane and out-of-plane anisotropy comprised of Thiessen polygons were generated with Voronoi tessellation, using a grain size of 200 nm. The material parameters were chosen to be exchange constant A = 10 pJ m –1 , Gilbert damping α = 0.3, saturation magnetization M s = 630 kA m –1 along c -axis, M s = 730 kA m –1 along ab -plane, and D = 1.2 mJ m –2 and K u = 2.5 kJ m –3 in the out-of-plane regions, and periodic boundary conditions were applied in the lateral film dimensions.…”

Magnetic Imaging and Domain Nucleation in CrSBr Down to the 2D Limit

“…Due to the absence of inversion symmetry between interacting Cr‐based atoms, [ 43 ] the DM contribution was included, second term in Equation (), with DM unit vectors parallel to the a ‐th (mediating $${\mathcal{J}}_3$$) and b ‐th (mediating $${\mathcal{J}}_1$$) axes, being given by D 1 = 0.07 and D 3 = 0.18 meV, respectively. [ 19 ] Moreover, the long‐range dipole‐dipole interaction, $${\mathcal{H}}_{{\mathrm{dip}}}$$, which can be expressed as: $$$$\begin{equation} {\mathcal{H}}_{\mathrm{dip}}=-\frac{{\mu}_{0}{\mu}_{S}^{2}}{4\pi}\sum _{i\ne j}\frac{3\left({\mathbf{M}}_{i}\cdot {\widehat{\mathbf{r}}}_{\mathit{ij}}\right)\left({\mathbf{M}}_{j}\cdot {\widehat{\mathbf{r}}}_{\mathit{ij}}\right)-\left({\mathbf{M}}_{i}\cdot {\mathbf{M}}_{j}\right)}{{\left|{\mathbf{r}}_{\mathit{ij}}\right|}^{3}} \end{equation}$$$$had been included for completeness despite the fact that we focused on the investigation of a purely AFM sample, using the tensorial approach for it, [ 31,44,45 ] being $${\widehat{\mathbf{r}}}_{\mathit{ij}}$$ the unit vector position joining the i ‐ and j ‐th magnetic atoms. It should be noted that, in the previous expression, in addition to the presence of the vacuum magnetic permeability, µ 0 , the atomic magnetic moment, µ S , was involved, to which the value µ S = 2.88 µ B has been assigned in consonance with the bulk scenario, [ 19 ] being µ B the Bohr magneton.…”

“…Apart from this, in the literature there were two opposing positions about the two‐ion contributions, since, on the one hand, it had been reported that they share the same order of magnitude as the on‐site ones, inducing that the a ‐th axis becomes the easiest one in the system, [ 42 ] while, on the other hand, it had been postulated that the exchange interactions were practically isotropic and do not contribute substantially to the magnetic anisotropy distribution of a bilayer system. [ 45 ] It should also be noted that the experimentally reported atomic lattice spacings given by a = 3.50 and b = 4.76 Å were employed, taking into account that the height of the primitive cell is c = 7.96 Å. [ 19,20 ]…”