Dynamical response of antiferromagnets in an oblique magnetic field: Application to surface magnons

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Abstract
We discuss the dynamical response of the two-sublattice, uniaxial Heisenberg antiferromagnet, for the case where an external magnetic field is applied in arbitrary direction relative to the easy axis. For the case where the external field is perpendicular to this axis, we obtain simple expressions for the nonzero elements of the magnetic-susceptibility tensor. These are used to discuss the properties of spin waves on the surface of an antiferromagnet, for the case where both the easy axis and the external magnetic field are parallel to the surface, but mutually perpendicular.