First-principles studies of spin-phonon coupling in monolayer Cr2Ge2Te6

Abstract

We perform systematic first-principles calculations to investigate the spin-phonon coupling (SPC) of Cr2Ge2Te6 (CGT) monolayer (ML). It is found that the Eg phonon mode at 211.8 cm -1 may have a SPC as large as 3.19 cm -1 , as it directly alters the superexchange interaction along the Cr-Te-Cr pathway. Furthermore, the strength of SPC of the CGT ML can be further enhanced by an in-plane compressive strain. These results provide useful insights for the understanding of SPC in novel two-dimensional magnetic semiconductors and may guide the design of spintronic and spin Seebeck materials and devices.In Eq. (2) and (3), spin S for each Cr atom is 3/2. Our calculations show that 1 J =4.92 meV, 2 J =-0.31 meV, and 3 J =0.01 meV, which agrees well with previous studies [15,37]. The large FM 1 J results from the competition between the direct exchange between Cr-Cr sites and the superexchange mediated through the Te ions, and strongly depends on the Cr-Cr distance. It is conceivable that J1 changes when the CGT lattice is either stretched or compressed. This is confirmed in Fig. 2(a) which shows that 1 J , 2 J and 3 J increase rapidly with lattice expansion in a range from 6.69 Å to 6.97 Å. Especially, the slope of the black curve in Fig. 2(a) indicates that the coefficient of the variation of J1 with lattice expansion is as large as 21.13 meV/Å. Furthermore, it is obvious that the FM state becomes more stable when the lattice is

Magnetic anisotropy and ferroelectric-driven magnetic phase transition in monolayer Cr2Ge2Te6

“…1(c)), which is consistent with the previous works. 41,59 Additionally, the thermal stability of ML-CGT lattice is assessed by performing ab initio molecular dynamics (MD) simulations. We use a 3 × 3 supercell to carry out the individual simulations at a temperature of 300 K within 20 ps.…”

“…More recently, Su et al 40 predict that ML-CGT prefers out-of-plane MAE with the Curie temperature ( T C ) of 19 K predicted via Ising Hamiltonian model. At the same time, Hou et al 41 point out that the magnetic-exchange interaction J and spin-wave stiffness quickly increase as lattice constant expands. Obviously, the magnetic anisotropy and T C of ML-CGT, which are essential for establishing long-range FM order in 2D limits, have not yet been comprehensively understood up to date.…”

Large‐Area Epitaxial Film Growth of van der Waals Ferromagnetic Ternary Chalcogenides

“…The alignment of the Cr magnetic moments indicates that the easy ferromagnetic axis is the out-of-plane (c) axis, although the in-plane (ab-plane) can have a weak magnetization. [41,42] Such magnetic anisotropy of the Cr 2 Ge 2 Te 6 and Cr 2 Si 2 Te 6 thin films was investigated by measuring the temperature-dependent magnetization M(T) under an external field (H) of 100 Oe. We applied the field parallel to the c-axis and the ab-plane (Figures 5c,d).…”

van der Waals Magnets: Material Family, Detection and Modulation of Magnetism, and Perspective in Spintronics

“…[ 72 ] The zone‐folding effects may also lead to peak splitting as a result of magnetic ordering. [ 55 ] Besides, the phonon frequency or linewidth exhibits abnormal variations near the transition temperature of vdW magnets, [ 74 ] indicative of the presence of magnetism, which is related to the interaction between the exchange integral and the lattice vibration. [ 72 ] From temperature‐dependent Raman measurements shown in Figure a, it can be seen that the phonon frequency of A 1g mode in Fe 3 GeTe 2 shows a clear deviation from the fitting line when the temperature is below T C , implying an abnormal softening of phonon with the onset of magnetism.…”