  We analyze the thermodynamic properties of antiferromagnetic solids subjected
to a combination of mutually orthogonal uniform magnetic and staggered fields.
Low-temperature series for the pressure, order parameter and magnetization up
to two-loop order in the effective expansion are established. We evaluate the
self-energy and the dispersion relation of the dressed magnons in order to
discuss the impact of spin-wave interactions on thermodynamic observables.
