Disorder Effect Of The Stripe Phase Of Nickel Oxide Materials Research

A wide variety of experimental results and theoretical investigations in recent years have demonstrably indicated that strongly correlated perovskite oxides have dominant states that are not spatially homogeneous. The spontaneous stripe ordered structure in superconducting cuprate and insulating nickelate occurs in cases in which several physical interactions—spin, charge, and lattice—are simultaneously active. The stripe phase seems crucial to understand the high-temperature superconductivity. In this dissertation, we studied the effects of size disorder and doping disorder on the stripe ordered La_5/3Sr_1/3NiO₄. The structural, transport and magnetic properties were investigated and compared. Some important results were obtained and the detailed experimental results and discussions are shown as follows:In chapter 1, the recent progresses on the stripe phase in superconducting cuprate, especially, on the relationships between stripe and superconductivity were simply reviewed. In addition, many experimental results of the diagonal stripe ordering in layered nickelate were introduced. Besides, some still unclear phenomena were illustrated and discussed.In chapter 2, we synthesized the nanosized La_5/3Sr_1/3NiO₄ particles by a sol-gel method and investigated their structural, magnetic and transport properties. Compared with the bulk sample, it is found that the long-range charge order is destroyed in the nanosized particles. Accompanied by the disappearance of the antiferromagnetic spin-ordered state, a ferromagnetic-like phase emerges at～23 K. The infrared transmission spectrum result demonstrated that the structural distortion on the surface of particles is the reason of the increased ferromagnetism. Furthermore, the spin glass/spin reorientation transition temperature T_CA for the～100 nm particles is～65 K which is～12 K higher than that of the bulk. This suggests that instead of the stabilization of charge order, the structural disorder may have a dramatic effect on the complex magnetic transition in the stripe phase nickelate.In chapter 3, A-site cation disorder effects of stripe order Ln_5/3M_1/3NiO₄ (Ln=La, Nd; M=Ca, Sr, Ba) are investigated. With the increase of the degree of disorder, the charge ordered transition temperature decreases gradually. In contrast to charge ordering, a visible antiferromagnetic spin hump is induced by A-site cation disorder which is potentially responsible for the enhancement of the pseudogap and the depression of the superconducting T_C observed in cuprate. In addition, two different transition temperatures related with the spin order are identified and discussed. Besides, the increase in the low temperature glass-like transition temperature hints that the quenching disorder has a prominent influence on the nonequilibrium magnetic feature. The nonlinear conductance effect was also observed in our research, but we demonstrated that the anomalous transport effect can be attributed to joule heating and the charge stripe order in the A-site disordered nickelate is very robust.In chapter 4, we compared the effect of size disorder and doping disorder on stripe ordered structure and found that the different disorders have distinct influence on charge ordering in nickelate. Importantly, we demonstrated that the short-range charge order in nanosized La_5/3Sr_1/3NiO₄ particles still exists and appears at the same temperature in which the long-range charge order forms on bulk...