Spin waves in the two-dimensional honeycomb lattice XXZ-type van der Waals antiferromagnet CoPS3

Abstract

The magnetic excitations in CoPS 3 , a two-dimensional van der Waals (vdW) antiferromagnet with spin S=3/2 on a honeycomb lattice, has been measured using powder inelastic neutron scattering.Clear dispersive spin waves are observed with a large spin gap of ~13 meV. The magnon spectra were fitted using an XXZ-type J 1 -J 2 -J 3 Heisenberg Hamiltonian with a single-ion anisotropy assuming no magnetic exchange between the honeycomb layers. The best-fit parameters show ferromagnetic exchange J 1 =-2.08 meV and J 2 =-0.26 meV for the nearest and second-nearest neighbors and a sizeable antiferromagnetic exchange J 3 =4.21 meV for the third-nearest neighbor with the strong easy-axis anisotropy K=-2.06 meV. The suitable fitting could only be achieved by the anisotropic XXZ-type Hamiltonian, in which the exchange interaction for the out-of-plane component is smaller than that for the in-plane one by a ratio α=J z /J x =0.6. Moreover, the absence of spin-orbit exciton around 30 meV indicates that Co 2+ ions in CoPS 3 have a S=3/2 state rather than a spin-orbital entangled J eff =1/2 ground state. Our result directly shows that CoPS 3 is an experimental realization of the XXZ model with a honeycomb lattice in 2D vdW magnets.

Ferromagnetism Induced by Magnetic Dilution in Van der Waals Material Metal Thiophosphates

“…The spin-orbit coupling contributes to the magnetic anisotropy resulting in the Ising-type and XXZ-type antiferromagnets, respectively. [28,31] According to Mermin-Wager theory, introduction of anisotropy can stabilize the 2D magnetic order. Raman spectroscopy suggests that the magnetism in FePS 3 persists down to monolayer, making it the most promising candidate for spintronic applications.…”

Spin Waves and Dirac Magnons in a Honeycomb Lattice Zig-zag Antiferromagnet BaNi2(AsO4)2

“…One unsolved quest is to determine magnetic exchange couplings giving rise to the zig-zag AF order, which is necessary to extract Kitaev interactions in α-RuCl 3 26 . Actually, this quest has not been completely solved in all 2D honeycomb lattice magnets with a zigzag AF ground state, despite many compounds have been studied [27][28][29][30][31][32][33] . Inelastic neutron scattering (INS) experiments carried out on powder samples of some of these compounds provided constraints on the magnetic exchange couplings 31,34,35 .…”

“…Actually, this quest has not been completely solved in all 2D honeycomb lattice magnets with a zigzag AF ground state, despite many compounds have been studied [27][28][29][30][31][32][33] . Inelastic neutron scattering (INS) experiments carried out on powder samples of some of these compounds provided constraints on the magnetic exchange couplings 31,34,35 . Nevertheless, no measurements on single crystals have conclusively unveiled the magnetic couplings giving rise to the zig-zag AF structure.…”

Excitations in the ordered and paramagnetic states of honeycomb magnet Na2Co2TeO6

“…Given the relatively weak SOC in 3d transition metals, the pseudospin picture is not necessarily adequate for describing the low-energy physics in Co-based compounds [30,64]. To check this, we inspect the crystal-field excitations of Na 2 Co 2 TeO 6 .…”

“…1(e). A zeroth-order approximation to these excitations is the process of exciting electrons from J eff = 1/2 to J eff = 3/2 states [30,47,64], schematically showed in the inset of Fig. 1(e).…”