NSRRC Activity Report 2022

Neutron Science 075 M agnetic excitation has been investigated in two models, namely a localized electron model and an itinerant electron model. However, magnetic excitation behavior has been elusive when both local moments and itinerant electrons are present in the intermediate range. In the local or itinerant extreme, magnetic excitations can be described by the Heisenberg model, which treats Fig. 1 : (a,b) Constant- E scans at various energies along [1, 0] and [1, 1] directions, respectively, with E i = 222 meV collected at 4SEASONS, J-PARC. For each scan, the energy intervals at selected energies were chosen to be 5 meV, and l was integrated over −10 ≤ l ≤ 10 r.l.u. (c,d) Spin dispersions along [1, 0] and [1, 1] directions, respectively. The peak centers were extracted from fittings to the constant- E scans as shown in (a) and (b). Dotted lines indicate the Brillouin zone boundaries. Regions are shaded for the reader’s convenience. (e,f) DFT calculations of spin-up and spin- down bands in the ferromagnetic state, respectively. (g) Diagram for particle-hole (p-h) scattering processes. The red and green bands with up and down spins, respectively, are simulated bands on the basis of a tight-binding model on a triangular lattice. These bands are plotted over (e) and (f) for comparison. Black arrows represent the p-h scattering occurring between bands with different spin directions. The inset shows the corresponding Fermi surface and the wave vectors corresponding to the most significant scattering near the Fermi level. Calculated bare (h) and RPA-renormalized (i) spin excitation spectra below 100 meV induced by the p-h scattering processes in (g). [Reproduced from Ref. 1] Evidence on the Dual Nature of Magnetic Excitations in a VdWMetallic Ferromagnet Fe 2.72 GeTe 2 Bao et al. provided evidence that spin-wave excitations, particle-hole continuum, and Kondo-lattice behaviour coexist in a d-electron system and elucidated the nature of magnetism in correlated electronic materials electron spins as localized moments, or by the itinerant electron model, in which the exchange interaction between electrons leads to an unequal number of electrons with up versus down spins. Song Bao (Nanjing University, China) and coworkers used the cold neutron triple axis spectrometer SIKA at Australian Centre for Neutron Scattering, Australia's Nuclear Science and Technology Organisation (ACNS, ANSTO), 1 to investigate the low-energy mode.