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

Pressure effects on the electronic, magnetic properties and structure of several typical colossal magnetoresistive manganites, La_{0.60}Y_{0.07}Ca_{0.33}MnO_3, Pr_{1-x}Ca_xMn0_3 (X = 0.25, 0.30, 0.35), Nd_{1-x}Sr_xMnO_3 (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_{0.60}Y_{0.07}Ca_{0.33}MnO_3, 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_{0.25}MnO_3, with pressure increase, T_{mi}, increases and T_c decreases below P* and the trend is reversed above P*. In Pr_{0.7}Ca_{0.3}MnO_3, 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_{0.60}Y_{0.07}Ca_{0.33}MnO_3, 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-x}Ca_xMnO_3 compounds, charge ordering is suppressed below P*. Above P*, an insulating state with unknown conducting mechanism is induced. In Nd_{1-x}Sr_xMnO_3, 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-x}Ca_xMnO_3 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.

Name thesis:degree_name

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

Discipline thesis:degree_discipline

Federated Physics Department

Year

2003

Author dc:creator

• Cui, Congwu

Contributors dc:contributor

• Trevor Tyson
• Gordon A. Thomas
• Ken K. Chin

• high pressure
• manganite
• coloccal magnetoresistance
• correlated elctron system
• structure
• electron transport
• Other Physics

Repository record dc:identifier

https://digitalcommons.njit.edu/dissertations/574

OAI identifier oai:identifier

oai:digitalcommons.njit.edu:dissertations-1629