Nonlinear-nonreciprocal spectroscopy of antiferromagnets

Summary form only given. Nonreciprocal effects are caused by breaking of time-inversion symmetry. Nonlinear spectroscopy is an excellent tool to study nonreciprocal effects as, for example, antiferromagnetic (afm) ordering, as was recently shown for Cr/sub 2/O/sub 3/. The sign of the nonlinear optical susceptibility tensor can be measured by second harmonic generation (SHG) if there is at the same time a SH-contribution from a time invariant susceptibility tensor.