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Strong interlayer magnetic exchange coupling in La3Ni2O7-δ revealed by inelastic neutron scattering
![The lattice structure and spin excitation spectra of powder La3Ni2O7-δ (a)The lattice structure of La3Ni2O7-δ;(b)The momentum dependence of the dynamical susceptibility χ'' within E = [2.5, 3.5] meV;(c)The subtraction of the low- and high-temperature spin excitations;(d)and(e)The schematic of single spin-charge stripe AFM order and the calculated spin-excitation spectrum from SpinW with SJ2 = 3.0, SJ3 = 1.7, and SJ⊥ = 57.5 meV;(f)and(g)The schematic of double spin stripe AFM order and the calculated spin-excitation spectrum from SpinW with SJ3 = 3.6, and SJ⊥ = 63.9 meV. Credit: Science China Press Strong interlayer magnetic exchange coupling in La3Ni2O7-δ revealed by inelastic neutron scatteringr](https://scx1.b-cdn.net/csz/news/800a/2024/strong-interlayer-magn.jpg)
Recently, an inelastic neutron scattering work on the bilayer nickelate La3Ni2O7-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 La3Ni2O7-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. These results can be explained to be from strong interlayer and weak intralayer magnetic couplings of stripe-type antiferromagnetic orders. 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-Tc 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, whose vacancies can break the interlayer couplings directly, and further break the pressure-induced high-Tc superconductivity.
Thus, this work not only studies the spin excitations of La3Ni2O7-δ at ambient pressure, determines the unique magnetic couplings in bilayer nickelates, but also provides crucial experimental evidences for understanding the high-Tc mechanism and the role of apical oxygens.
More information: Tao Xie et al, Strong interlayer magnetic exchange coupling in La3Ni2O7− revealed by inelastic neutron scattering, Science Bulletin (2024). DOI: 10.1016/j.scib.2024.07.030
Provided by Science China Press