The New Jersey Institute of Technology's
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Title:	High pressure effects on electron transport and structure of colossal magnetoresistive materials
Author:	Cui, Congwu
View Online:	njit-etd2003-071 (xiv, 162 pages ~ 10.4 MB pdf)
Department:	Federated Physics Department of NJIT and Rutgers-Newark
Degree:	Doctor of Philosophy
Program:	Applied Physics
Document Type:	Dissertation
Advisory Committee:	Tyson, Trevor (Committee chair) Thomas, Gordon A. (Committee member) Chin, Ken K. (Committee member) Federici, John Francis (Committee member) Wu, Zhen (Committee member)
Date:	2003-05
Keywords:	high pressure manganite coloccal magnetoresistance correlated elctron system structure electron transport
Availability:	Unrestricted
Abstract:	Pressure effects on the electronic, magnetic properties and structure of several typical colossal magnetoresistive manganites, La0.60Y0.07Ca0.33MnO3, Pr1-xCaxMn03 (X = 0.25, 0.30, 0.35), Nd1-xSrxMnO3 (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 La0.60Y0.07Ca0.33MnO3, pressure induces a local atomic structure transformation at a critical point P*, and hence, a non-monotonic change in metal insulator (MI) transition temperature (Tmi) and spin state. In Pr0.75Ca0.25MnO3, with pressure increase, Tmi, increases and Tc decreases below P* and the trend is reversed above P*. In Pr0.7Ca0.3MnO3, pressure induces reentrant electronic and magnetic states: between ~0.8-5 GPa, TmI, and Tc are coupled and have a behavior similar to La0.60Y0.07Ca0.33MnO3, outside of this range, TmI and Tc are decoupled and at low and high pressure the material is insulating. In all three Pr1-xCaxMnO3 compounds, charge ordering is suppressed below P*. Above P*, an insulating state with unknown conducting mechanism is induced. In Nd1-xSrxMnO3, at x = 0.45, in addition to the effect on TmI, pressure possibly induces an A-type antiferromagnetic phase. For x = 0.5, the charge ordering transition temperature is increased, which is different from Pr1-xCaxMnO3 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.