Optical determination of the antiferromagnetic exchange constant between nearest-neighbor ${\mathrm{Mn}}^{2+}$ ions in ${\mathrm{Zn}}_{0.95}$${\mathrm{Mn}}_{0.05}$Te

Zeeman splittings of the free exciton in ${\mathrm{Zn}}_{0.95}$ ${\mathrm{Mn}}_{0.05}$Te have been measured at 1.4 K with dc magnetic field B up to 19.3 T, using magnetoreflectance in the Faraday configuration. The splitting between the highest- and lowest-energy Zeeman components of the exciton follows a modified Brillouin function at low values of B≲10 T. The first of the expected five steps due to the magnetic-field-induced alignment of the antiferromagnetically coupled nearest-neighbor (NN) pairs was observed at $B_1$=15.0±0.6 T. Ignoring the effect of internal fields due to distant-neighbor ${\mathrm{Mn}}^{2+}$ ions on NN pairs, we deduce the NN exchange constant ${\mathit{J}}_{\mathrm{NN}\mathrm{\simeq }}$-(1/2)g${\mathrm{\mu }}_{\mathrm{B}}$ ${\mathrm{B}}_1$=-10. 1±0.4 K, in good agreement with that obtained from magnetization measurements.