PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Electronic Structure of Pr 1−x Ca x MnO 3 80 measurements are published elsewhere [10, 25]. There are also three polycrystalline samples (PrMnO 3 , CaMnO 3 and Pr 0.16 Ca 0.14 MnO 3 ) used for different studies. Which were prepared by the standard solid state reaction method. The details of the sample preparation is published elsewhere [26]. Consolidated results of these studies are presented in the phase diagram shown in Fig. 4.1 [27]. Angle integrated ultraviolet photoemission measurements were performed by using an Omicron mu-metal ultra high vacuum system equipped with a high intensity vacuum ultraviolet source (HIS 13) and a hemispherical electron energy analyzer (EA 125 HR). At the He I (21.2 eV) line, the photon flux was of the order of 10 16 photons/sec/steradian with a beam spot of 2.5 mm diameter. The Fermi energies (E F ) for all measurements were calibrated by using a freshly evaporated Ag film on a sample holder. The total energy resolution, estimated from the width of the Fermi edge, was about 80 meV. The XPS measurements were performed using a twin anode Mg/Al x-ray source (DAR 400) in the same chamber as of UPS. In our measurements we have used the Mg Kα line with photon energy 1253.6 eV and the resolution was about 1.0 eV. The samples were repeatedly scraped by using a diamond file inside the chamber under a base vacuum of ∼ 1.0 x 10 −10 mbar. The negligible intensity found for the ∼ 9.5 eV bump [16] in the UPS spectra ensures the cleanliness of our sample surface. For the temperature dependent measurements, the samples were cooled by pumping liquid nitrogen through the sample manipulator fitted with a cryostat. The sample temperatures were measured by using a silicon diode sensor touching the bottom of the sample holder. The IPES measurements were performed by using an electrostatically focused electron gun of Stoffel Johnson design and an acetone gas filled band pass Geiger Muller counter with a CaF 2 window [28, 29]. These measurements were carried out in the isochromat mode in which the photon energy is fixed at 9.9 eV and kinetic energy of the incident electrons is varied in 0.05 eV steps. Overall resolution of the IPES measurements were estimated [29] to be approximately 0.55 eV. 4.3 Results and Discussion 4.3.1 The UPS study of Pr 1−x Ca x MnO 3 , x = 0.2, 0.33 and 0.4 Neutron diffraction studies [27] on Pr 1−x Ca x MnO 3 have shown that the compositions with x = 0.2 and x = 0.4 are FM and AFM respectively (Fig. 4.1) while the x = 0.33 has co-existing FM and AFM phases [14, 15]. The ground state of x = 0.33 has been
Electronic Structure of Pr 1−x Ca x MnO 3 81 identified to be an inhomogeneous state below T CO . The x = 0.4 is above the critical doping (x c ) found in the Pr 1−x Ca x MnO 3 system and is homogeneous in nature. (a) 300 K C B (b) 77 K C B Intensity (arb. units) A 1.0 0.4 0.33 Intenisty (arb. units) A 1.0 0.4 0.33 0.2 0.2 0.0 0.0 10 8 6 4 2 0 10 8 6 4 2 0 Binding Energy (eV) Binding Energy (eV) Figure 4.2: The angle integrated valence band photoemission spectra of the Pr 1−x Ca x MnO 3 (x = 0.0, 0.2, x = 0.33, x = 0.4 and x = 1.0) samples taken at room temperature and 77K using He I photons (21.2 eV). Figure 4.2 shows the angle integrated valence band photoemission spectra of the Pr 1−x Ca x MnO 3 (x = 0.2, x = 0.33 and x = 0.4) samples taken at room temperature and 77K. The figure also shows the spectra of the end compositions of this system (x = 0.0 and x = 1.0). It may be noted from the phase diagram that the compositions with x = 0.2, x = 0.33 and x = 0.4 are PM insulators at 300K and FM/AFM insulators at 77K. Intensities of all the spectra shown in both the panels were normalized and shifted along the ordinate axis by a constant value for clarity. All the features seen in the spectra are dominated by the states due to the Mn 3d - O 2p hybridized orbitals. The two prominent features, one at ∼ 3.5 eV (marked B) and another at ∼ 5.6 eV (marked C), are primarily due to the O 2p nonbonding states and the Mn 3d - O 2p bonding states [30]. The feature closest to the E F , which appear as a tail at
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SPECTROSCOPIC INVESTIGATIONS OF THE
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iii To My Parents
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Maharana, P. Khare, D. K. Basa, K.
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List of Publications/Preprints [1]
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Synopsis The perovskite type mangan
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to the t 2g and e g spin-up states
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Bibliography [1] R. von Helmolt, J.
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Contents CERTIFICATE Acknowledgemen
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List of Figures 1.1 Temperature dep
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2.2 Schematic view of the energetic
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3.4 O K edge x-ray absorption spect
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Chapter 1 Introduction 1
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Introduction 3 The temperature and
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Introduction 5 Figure 1.2: Schemati
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Introduction 7 Figure 1.4: A schema
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Introduction 9 Figure 1.6: Schemati
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Introduction 11 Figure 1.8: Differe
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Introduction 13 Figure 1.10: A sche
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Introduction 15 Figure 1.12: Schema
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Introduction 17 Figure 1.13: Phase
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Bibliography [1] R. von Helmolt, J.
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Introduction 21 [31] Damien Saurel,
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Chapter 2 Experimental Techniques 2
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Experimental Techniques 25 Figure 2
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Experimental Techniques 27 Let us n
Page 51 and 52: Experimental Techniques 29 and G(k,
Page 53 and 54: Experimental Techniques 31 Figure 2
Page 55 and 56: Experimental Techniques 33 point wi
Page 57 and 58: Experimental Techniques 35 negative
Page 59 and 60: Experimental Techniques 37 ∆E = E
Page 63 and 64: Experimental Techniques 41 ( ) dσ
Page 65 and 66: Experimental Techniques 43 The expe
Page 67 and 68: Experimental Techniques 45 are weld
Page 77 and 78: Bibliography [1] H. Hertz, Ann. Phy
Page 79 and 80: Experimental Techniques 57 [35] K.
Page 81 and 82: Chapter 3 Electronic Structure of P
Page 83 and 84: Electronic Structure of Pr 0.67 Ca
Page 95 and 96: Bibliography [1] I. G. Deac, J. F.
Page 99 and 100: Chapter 4 Electronic Structure of P
Page 101: Electronic Structure of Pr 1−x Ca
Page 105 and 106: Electronic Structure of Pr 1−x Ca
Page 119 and 120: Electronic Structure of Ca 0.86 Pr
Page 127 and 128: Bibliography [1] C. Zener, Phys. Re
Page 131 and 132: Summary and Conclusions 109 In this
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PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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