High pressure effects on electron transport and structure of colossal magnetoresistive materials

Author

Congwu Cui, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

Spring 5-31-2003

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Federated Physics Department

First Advisor

Trevor Tyson

Second Advisor

Gordon A. Thomas

Third Advisor

Ken K. Chin

Fourth Advisor

John Francis Federici

Fifth Advisor

Zhen Wu

Abstract

Pressure effects on the electronic, magnetic properties and structure of several typical colossal magnetoresistive manganites, La_0.60Y_0.07Ca_0.33MnO₃, Pr_1-xCa_xMn0₃ (X = 0.25, 0.30, 0.35), Nd_1-xSr_xMnO₃ (x = 0.45, 0.50), were explored through high pressure resistivity and structure measurements. It was shown that pressure up to ~7 GPa induces more complicated charge, spin and lattice state changes than in the low pressure range explored previously. In La_0.60Y_0.07Ca_0.33MnO₃, pressure induces a local atomic structure transformation at a critical point P*, and hence, a non-monotonic change in metal insulator (MI) transition temperature (T_mi) and spin state. In Pr0.75Ca_0.25MnO₃, with pressure increase, T_mi, increases and T_c decreases below P* and the trend is reversed above P*. In Pr_0.7Ca_0.3MnO₃, pressure induces reentrant electronic and magnetic states: between ~0.8-5 GPa, T_mI, and T_c are coupled and have a behavior similar to La_0.60Y_0.07Ca_0.33MnO₃, outside of this range, T_mI and T_c are decoupled and at low and high pressure the material is insulating. In all three Pr_1-xCa_xMnO₃ compounds, charge ordering is suppressed below P*. Above P*, an insulating state with unknown conducting mechanism is induced. In Nd_1-xSr_xMnO₃, at x = 0.45, in addition to the effect on T_mI, pressure possibly induces an A-type antiferromagnetic phase. For x = 0.5, the charge ordering transition temperature is increased, which is different from Pr_1-xCa_xMnO₃ system. The effects of chemical doping (bandwidth) and pressure are not equivalent in the high pressure range. This is unlike the results in the low pressure range acquired by other groups previously. A universal P* exists for samples with metal-insulator transitions.

Recommended Citation

Cui, Congwu, "High pressure effects on electron transport and structure of colossal magnetoresistive materials" (2003). Dissertations. 574.
https://digitalcommons.njit.edu/dissertations/574