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

The structural, magnetic and transport properties of La0.5Sr0.5MnO2.88 and La0.5Sr0.5Mn0.5Ti0.5O3 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 La0.5Sr0.5MnO3 sample. Ceramic material based on La0.5Sr0.5MnO2.88 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 eg 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 μexp/μcal ratio for La0.5Sr0.5MnO2.88, whereas the CO state is suppressed for La0.5Sr0.5Mn0.5Ti0.5O3 sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be ∼54:46, respectively.