Ultrasonic, Transport, and Magnetic Properties of NdSrMnCrO Perovskites.

The resistivity, magnetization and longitudinal ultrasonic velocity ( V) have been measured in single-phase polycrystalline NdSrMnCrO ( 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 shows two large stiffening just below the metal-insulator transition temperature T and the charge ordering temperature T, 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. With the Cr doping, the T 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 in these doping samples. The analysis suggests that the Cr doping enhances the double exchange between Mn and Mn, and thoroughly destroys the charge ordering state. [ABSTRACT FROM AUTHOR]