Masters Thesis Defense - Hydrostatic Pressure Effects on the Electrical Transport Properties of Pr_0.5Sr_0.5MnO₃

Who: Franz Rueckert

Time: 3:00pm, Monday 25th June, 2007

Place: P-250

Abstract: The electrical properties of single-crystalline Pr_0.5Sr_0.5MnO₃ were examined under hydrostatic pressures up to 2.0 GPa, in the temperature (T) range from 10 to 300 K. The magnetic and crystallographic phase diagrams of this material are quite complex. A transition from paramagnetic insulator to ferromagnetic (FM) metal takes place at the Curie temperature T_C = 255 K. Upon further cooling, the material transitions to an antiferromagnetic (AFM) insulating phase at the Néel temperature T_N = 161 K. The FM to AFM transition is accompanied by a large upward discontinuity in electrical resistivity (ρ), and by a crystallographic transformation. The electrical resistivity is quite sensitive to pressure in the whole temperature range studied. The application of pressure decreased T_C slightly and increased T_N considerably, while suppressing the discontinuity in ρ vs T at T_N. The suppression of the insulating AFM phase below T_N is accompanied by the suppression of the crystallographic Fmmm phase in favor of I4/mcm. An increase in orbital overlap and the straightening of Mn-O-Mn bond angles as the result of pressure serves to strengthen the double exchange process, thereby improving the electrical conductivity and stabilizing the FM phase. Extrapolation of the ρ vs T pressure data suggests the low temperature insulating AFM phase could be suppressed completely above 2.4 GPa.

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