PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Electronic Structure of Ca 0.86 Pr 0.14 MnO 3 100 Intensity (arb. units) A 30 K 70 K 110 K 220 K 300 K 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 Binding Energy (eV) Figure 5.2: The high resolution spectra of the near E F region of the valence band of Ca 0.86 Pr 0.14 MnO 3 for 30 K, 70 K, 110 K, 220 K and 300 K. This feature refers to the e g band. states due to the Mn 3d - O 2p hybridization. The broad feature appearing at ∼ 6 eV (marked D) is due to the bonding states of this hybridization while its non-bonding states appear as a shoulder at ∼ 3.2 eV (marked C). The peak at ∼ 2 eV (marked B) is due to the Mn 3d t 2g states of the MnO 6 octahedra [17]. The Mn 3d e g↑ states of the octahedra appear around ∼ 0.3 eV (marked A) in the spectra. It should be noted that the intensity of the peak B decreases with decrease of temperature while that of the feature A increases. These spectral weight shifts are characteristic of many CMR systems. The e g states lying close to the E F are important for the conductivity of this material. A high resolution spectra of the near E F region is presented in figure 5.2. As the temperature is lowered from 293 K the feature A starts appearing. Further, below the transition temperature T c (110 K), the intensity of A steeply increases and goes through a maximum. The 30 K spectrum again shows a smaller intensity for this feature compared to the one at 70 k. Interestingly, below the T c , the leading edges of the different spectra move towards the E F as we go down in temperature.
Electronic Structure of Ca 0.86 Pr 0.14 MnO 3 101 Mn 3d + O 2p Pr 5d, Ca 3d Mn 4sp, Pr 6sp Normalized Absorption (arb. units) 300 K 200 K 150 K 80 K 30 K 530 540 550 560 Photon Energy (eV) Figure 5.3: The O K-edge x-ray absorption spectra of the Ca 0.86 Pr 0.14 MnO 3 taken at 30 K, 80 K, 150 K, 200 K and 300 K. The pre-edge feature appears between 527 - 533 eV is mostly due to the strong hybridization between Mn 3d and O 2p orbitals, where most interest lies. Origin of other features are given in the text. This shifting of the valence band edges is a clear indication of increase in the width (W) of the e g band below the T c . In order to see the corresponding changes in the near E F unoccupied states we have taken the O K edge x-ray absorption spectra (XAS) of the Ca 0.86 Pr 0.14 MnO 3 sample at different temperatures (Fig. 5.3). Here, all the spectra have been normalized to the incoming intensity and absolute cross sections and are also corrected for selfabsorption and saturation effects. The spectra shows three broad features. The one between 527 eV to 533 eV, called the pre-edge feature in the O K edge spectra, is mostly due to the strong hybridization between Mn 3d and O 2p orbitals. The feature around 536.5 eV is due to the bands from hybridized Pr 5d and Ca 3d orbitals, while
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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
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Experimental Techniques 29 and G(k,
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Experimental Techniques 33 point wi
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Experimental Techniques 35 negative
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Experimental Techniques 37 ∆E = E
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Experimental Techniques 41 ( ) dσ
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Experimental Techniques 43 The expe
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Experimental Techniques 45 are weld
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Page 71 and 72: Experimental Techniques 49 Figure 2
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 and 102: Electronic Structure of Pr 1−x Ca
Page 119 and 120: Electronic Structure of Ca 0.86 Pr
Page 121: 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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