Optical investigations on {N(CH₃)₄}₂MnCL₄: A new phase transition at 90 K

Abstract

The phase transitions undergone by [N(CH₃)₄]₂ MnCl₄ crystals in the 10–300 K temperature range have been explored through the absorption and emission spectra as well as lifetime measurements. The present measurements confirm the existence of phase transitions at T_c3 = 268.7 K and T_c4 = 175.6 K and provide clear evidence of another (first order) phase transition at T_c5≃90K upon cooling and involving an hysteresis of δ_c5 = 12 K.

The sensitivity of each of the optical parameters is studied for every phase transition. For the P2₁/c11 → P112₁/n phase transition the lifetime gives a small hysteresis δ_c3 = 0.4 K.