Recently, an inelastic neutron scattering work on the bilayer nickelate La 3 Ni 2 O 7- δ polycrystal finished by a team from Sun Yat-sen University was published in Science Bulletin . The team employed neutron spectroscopy to study the magnetic ground state and spin dynamics of La 3 Ni 2 O 7- δ at ambient pressure. The neutron diffraction results show that there is no magnetic order down to 10 K. In the inelastic channel, they observed some weak spin excitations, which contain low-energy spin excitations at several millielectronvolts and almost non-dispersive high-energy spin excitations around 45 meV (see Fig. b and c). These results can be explained to be from strong interlayer and weak intralayer magnetic couplings of stripe-type antiferromagnetic orders (see Fig. d-g). The corresponding interlayer and intralayer magnetic couplings could be around 60 meV and 3~4 meV, respectively. These observations are quite different from that in cuprate and iron-based superconductors, which have dominant intralayer exchange couplings. To date, there are still a lot of debates about the high- T c mechanism in nickelates, but the consensus of most existed theories is that interlayer magnetic couplings play a key role. The super exchanges between two adjacent nickel layers are mediated by the apical oxygens (see Fig. a), whose vacancies can break the interlayer couplings directly, and further break the pressure-induced high- T c superconductivity. Thus, this work not only studies the spin excitations of La 3 Ni 2 O 7- δ at ambient pressure, determines the unique magnetic couplings in bilayer nickelates, but also provides crucial experimental evidences for understanding the high- T c mechanism and the role of apical oxygens.
See the article:
Strong interlayer magnetic exchange coupling in La 3 Ni 2 O 7- δ revealed by inelastic neutron scattering
https://doi.org/10.1016/j.scib.2024.07.030
Science Bulletin