Ultrasonic, Transport, and Magnetic Properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)Cr_xO_3 Perovskites

摘要

The resistivity, magnetization and longitudinal ultrasonic velocity (V_1) have been measured in single-phase polycrystalline Nd_(0.5)Sr_(0.5)Mn_(1-x)Cr_xO_3 (x = 0, 0.02, 0.05, 0.1) to clarify the Cr doping effect on the metal-insulator and charge ordering transitions. For x = 0 sample, the V_1 shows two large stiffening just below the metal-insulator transition temperature T_(MI) and the charge ordering temperature T_(CO), respectively. It is suggested that the former ultrasonic anomaly may originate from the spin-lattice effect and the dynamic Jahn-Teller effect, and the latter is due to the electron-lattice effect arising from the static Jahn-Teller effect of Mn~(3+). With the Cr doping, the T_(MI) shifts to lower temperature, the maximum of magnetization becomes smaller and the resistivity remains metallic type. Furthermore, only one stiffening of ultrasonic velocity is observed below T_(MI) in these doping samples. The analysis suggests that the Cr doping enhances the double exchange between Mn~(3+) and Mn~(4+), and thoroughly destroys the charge ordering state.