Research on charge-ordering state in La0.5Sr0.5MnO2.88 and La0.5Sr0.5Mn0.5Ti0.5O3 systems

The structural, magnetic and transport properties of La_0.5Sr_0.5MnO_2.88 and La_0.5Sr_0.5Mn_0.5Ti_0.5O₃ samples have been investigated systematically. Indeed, this series has been considered to understand the influence of physical parameters such as oxygen deficiency and titanium doping effect in undoped La_0.5Sr_0.5MnO₃ sample. Ceramic material based on La_0.5Sr_0.5MnO_2.88 exhibits interesting behaviours of charge-ordering (CO), ferromagnetic (FM) states and a good conductivity down to the lowest temperatures. The substitution of Ti for Mn destroyed drastically the CO, damaged the motion of itinerant e_g electrons and changed the local parameters of perovskite cell. A change of the structure from tetragonal to rhombohedral symmetry is observed causing a weakening of double-exchange interaction. The experiment results show that the suppression of the CO is sensitive to the variety of Mn³⁺/Mn⁴⁺ ratio. In a field of 8 T at 10 K, FM and CO phase can be evaluated to be ∼20:80 according to the μ_exp/μ_cal ratio for La_0.5Sr_0.5MnO_2.88, whereas the CO state is suppressed for La_0.5Sr_0.5Mn_0.5Ti_0.5O₃ sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be ∼54:46, respectively.