Ultrasonic, Transport, and Magnetic Properties of Nd0.5Sr0.5Mn1-xCrxO3 Perovskites

The resistivity, magnetization and longitudinal ultrasonic velocity (V (l)) have been measured in single-phase polycrystalline Nd0.5Sr0.5Mn1-x Cr (x) O-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 (l) 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 Mn3+. 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 Mn3+ and Mn4+, and thoroughly destroys the charge ordering state.