  Metal-insulator transitions in pyrochlore iridates (A2Ir2O7) are believed to
occur due to subtle interplay of spin-orbit coupling, geometric frustration,
and electron interactions. In particular, the nature of magnetic ordering of
iridium ions in the insulating phase is crucial for understanding of several
exotic phases recently proposed for these materials. We study the spectrum of
magnetic excitations in the intermediate-coupling regime for the so-called
all-in/all-out magnetic state in pyrochlore iridates with non-magnetic A-site
ions (A=Eu,Y), which is found to be preferred in previous theoretical studies.
We find that the effect of charge fluctuations on the spin-waves in this regime
leads to strong departure from the lowest-order spin-wave calculations based on
models obtained in strong-coupling calculations. We discuss the characteristic
features of the magnetic excitation spectrum that can lead to conclusive
identification of the magnetic order in future resonant inelastic x-ray (or
neutron) scattering experiments. Knowledge of the nature of magnetic order and
its low-energy features may also provide useful information on the accompanying
metal-insulator transition.
