Structure, Magnetic, and Electrical Properties of La2NiO $_{4+\delta }$ Compounds

Abstract

We have investigated the structure, magnetic, and electrical properties, and the resistance switching effect (RSE) of La2NiO $_{{ {4+\delta }}}$ compounds with different excess oxygen levels of $\delta = 0.004 - 0.031$ . Our results showed the structure changes from tetragonal I4/mmm to orthorhombic Fmmm when reducing $\delta $ value from 0.011 to 0.006. The $M(H)$ curves measured at several temperatures exhibit a coexistence of the weak ferromagnetic and antiferromagnetic interactions. Two shoulders on $M(T)$ curves related to the spin and charge ordering have also been observed. These ordering temperatures depend strongly on $\delta $ value and they shift toward lower temperature with decreasing $\delta $ . All the samples exhibit a semiconductor behavior and their temperature dependences of the resistivity obey the variable-range-hoping model. Interestingly, the typical current–voltage characteristics of the samples show a hysteresis, which suggests an existence of the RSE. We have observed two different states of the resistance corresponding to high ( $R_{H}$ ) and low ( $R_{L}$ ) values. The resistance change ratio of the samples defined as 100% $\times [R_{H} - R_{L}]/R_{L}$ is found to be about 18%–57%, which depends on the value of $\delta $ in the samples.