Spin dynamics study in layered van der Waals single-crystal Cr2Ge2Te6

Abstract

We study the magnetisation dynamics of a bulk single crystal Cr2Ge2Te6 (CGT), by means of broadband ferromagnetic resonance (FMR), for temperatures from 60 K down to 2 K. We determine the Kittel relations of the fundamental FMR mode as a function of frequency and static magnetic field for the magnetocrystalline easy -and hard -axis. The uniaxial magnetocrystalline anisotropy constant is extracted and compared with the saturation magnetisation, when normalised with their low temperature values. The ratios show a clear temperature dependence when plotted in the logarithmic scale, which departs from the predicted Callen-Callen power law fit of a straight line, where the scaling exponent n, Ku(T ) ∝ [Ms(T )/Ms(2 K)] n , contradicts the expected value of 3 for uniaxial anisotropy. Additionally, the spectroscopic g-factor for both the magnetic easy -and hard -axis exhibits a temperature dependence, with an inversion between 20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we qualitatively discuss the observation of multi-domain resonance phenomena in the FMR spectras, at magnetic fields below the saturation magnetisation.arXiv:1903.00584v2 [cond-mat.mtrl-sci]

Long-range anisotropic Heisenberg ferromagnets and electrically tunable ordering

“…[4] We notice that the monolayer CrGeTe 3 has easy-axis anisotropy in agreement with the bulk and few-layer samples. [65][66][67][68] Expectedly the A z is weaker than that of CrI 3 (Table I). The nature of exchange coupling is slightly different from the chromium trihalides; J 1 remains ferromagnetic but with J 2 < 0 and J 3 > 0.…”

“…The case of CrGeTe 3 is interesting, which in bulk orders around 65 K [65][66][67][68] that is slightly higher than the CrI 3 counterpart. [29] While a layer-dependent T C is demonstrated, experimental observation of ordering has remained absent in the monolayer.…”

“…Within the anisotropic Heisenberg Monte Carlo, we determine the T C to be 53 K, which is somewhat higher than the bilayer (30 ± 5 K) but comparable to the fewlayer flakes, 52 ± 5 K for 5-layer CrGeTe 3 . [4] In the bulk crystal, the Cr-moment decreases rapidly with increasing temperature, from 2.8 µ B (2 K) to 2.3 µ B at 60 K. [67] Considering this fact, we have recalculated the T C using a smaller Cr-moment of 2.3 µ B along with the exchange parameters in the Table I, which produces a lower T C of 30.5 K (β = 0.191), which is in better agreement with the experiment. The calculated β for the monolayer is 0.213, which is in agreement with the bulk values of 0.177-0.242 that are experimentally determined.…”

Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe$_3$ and CrGeTe$_3$: towards intrinsic gap-tunability

“…All the inelastic neutron scattering experiments were performed by using a range of thermal and cold neutron triple-axis spectrometers, including PUMA at MLZ, FLEXX [51] References [17, 18, 23-27, 32, 34, 35, 40, 43, 47, 48, 52-60] V. ACKNOWLEDGMENTS The lattice parameter c = 20.681(75) Å for CrSiTe 3 and c = 20.603(99) Å for CrGeTe 3 at room temperature extracted from XRD (in Fig. S1[(a),(b)]) is quite consistent with the previous results [52][53][54]. From the temperature dependence of the magnetic susceptibility (shown in Fig.…”

Magnetic anisotropy and critical behavior of the quaternary van der Waals ferromagnetic material $\bf CrGe_δSi_{1-δ}Te_3$

“…Thus a linear fit gives the exponent n = 3.50 (10). The departure from Callen-Callen power law suggests the simple assumption of the single ion anisotropy is incomplete [23]. The additional magnetic exchange anisotropy should come elsewhere, such as the interplay between Kitaev interaction and single ion anisotropy [24], or anisotropic XXZ Heisenberg model [10,11].…”