PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...
PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...
PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...
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Introduction 17<br />
Figure 1.13: Phase diagram of Pr 1−x Ca x MnO 3 . Figure taken from ref. [44]<br />
resistivity vs. temperature graph of Pr 1−x Ca x MnO 3 (x = 0.3) under various magnetic<br />
fields [45] is shown in the Fig. 1.14(a). At low temperatures, changes in resistivity<br />
by several orders of magnitude can be observed. The stabilization of metallic state is<br />
realized upon the application of magnetic field. This state is ferromagnetic according<br />
to magnetization measurements, and thus it is curious to observe that a state not<br />
present at zero field in the phase diagram, is nevertheless stabilized at finite fields.<br />
The magnetic field effects on the other compositions of Pr 1−x CaxMnO 3 (x = 0.35,<br />
0.4 and 0.5) are also shown in the Fig. 1.14(b). The shape of the curves in Fig. 1.14<br />
present a large magnetoresistance effect, and a possible origin based on percolation<br />
between the CO- and FM-phase. Tomioka et. al. [46] showed that, as x grows away<br />
from x = 0.3, larger fields are needed to destabilize the charge-ordered state at low<br />
temperatures (e.g., 27 T at x = 0.50 compared with 4 T at x = 0.30).<br />
This thesis is based on the study of electronic structure of Pr 1−x Ca x MnO 3 series<br />
using different spectroscopic techniques.