  Using a model-independent low-energy effective field theory, we calculate the
free energy of three-dimensional antiferromagnets in a combination of mutually
perpendicular external magnetic and staggered fields at the
next-to-next-to-leading, two-loop order. Renormalization is carried out
analytically, and the renormalization group invariance of the result is checked
explicitly. The free energy is thus expressed solely in terms of temperature,
the external fields, and a set of low-energy coupling constants, to be
determined by experiment or by matching to the microscopic model of a given
concrete material.

Strongly Correlated Electrons;High Energy Physics - Phenomenology;High Energy Physics - Theory