Cooling-rate dependence of the antiferromagnetic domain structure of a single-crystal charge-ordered manganite

Abstract

The low-temperature phase of single crystals of Nd_0.5Ca_0.5MnO₃ and Gd_0.5Ca_0.5MnO₃ manganites is investigated by superconducting quantum interference device magnetometry. Nd_0.5Ca_0.5MnO₃ undergoes a charge-ordering transition at T_CO=245 K, and a long-range charge-exchange-type (CE-type) antiferromagnetic state is established at T_N=145 K. The dc magnetization shows a cooling-rate dependence below T_N, associated with a weak spontaneous moment. The associated excess magnetization is related to uncompensated spins in the CE-type antiferromagnetic structure and to the presence in this state of fully orbital ordered regions separated by orbital domain walls. The observed cooling rate dependence is interpreted to be a consequence of the rearrangement of the orbital domain state induced by the large structural changes occurring upon cooling.