PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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2.16 Schematic of the Si-photodiode. . . . . . . . . . . . . . . . . . . . . . 49 2.17 Schematic of the synchrotron radiation. . . . . . . . . . . . . . . . . . 50 2.18 Schematic representation of an insertion device. . . . . . . . . . . . . 51 2.19 Optical layout of the WERA soft x-ray beam line, ANKA. . . . . . . 52 2.20 Optical layout of the BEAR beam line. . . . . . . . . . . . . . . . . . 53 2.21 Optical layout of the BACH beam line. . . . . . . . . . . . . . . . . . 53 2.22 The variable included angle monochromator : the combined movement of PM1 (plane mirror) and one of the four spherical gratings SG1(-4) leads to the monochromatization of the light keeping both the entrance and exit slit fixed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3.1 Valence band photoemission spectra of Pr 0.67 Ca 0.33 MnO 3 taken using He I photon energy (21.2 eV) at 77 (solid line), 110 (dotted), 150 (dashed), 220 (dot-dashed), and 300 K (double-dot dashed). All the spectra have been normalized and shifted along y-axis by a constant for clarity. The subbands around -1.2 (e g↑ ), -3.5 (t 2g↑ ), and -5.6 eV (e g↑ + t 2g↑ ) are marked as A, B, and C respectively. . . . . . . . . . . . . 63 3.2 High-resolution photoemission spectra of the near-E F region of the valence band of Pr 0.67 Ca 0.33 MnO 3 . In (a) the spectrum taken below T c (red) is compared with the normal state (300 K) spectrum (blue). The difference spectrum (green) obtained by subtracting the spectra at 300 K from 77 K and multiplied by 5 is also shown in the panel. Similarly, in (b), (c), and (d) the near-E F spectra taken at 110, 150, and 220 K are compared with that taken at 300 K. The feature in the difference spectra corresponds to the tail feature A (e g↑ ) in Fig. 3.1. . . . . . . . 64 3.3 Temperature dependence of the area of the three valence band features obtained from fitting the spectra with Lorentzian line shapes using a χ 2 iterative program. We have used an integral background, which was kept the same for all the spectra. The energy positions and FWHMs were determined by finding the best fit common to all the spectra by the iterative program. The final fit for all spectra at different temperatures were obtained with the same energy positions and FWHMs. (a), (b), and (c) correspond to the features A, B, and C positioned at -1.19, -3.49, and -5.63 eV with FWHMs 2.56, 1.93, and 1.37 eV respectively. 65 xx
3.4 O K edge x-ray absorption spectra of Pr 0.67 Ca 0.33 MnO 3 taken at 300 (solid line), 150 (dashed line), and 95 K (dotted). The pre-edge feature centered around 529.5 eV (marked by a box) is where most interest lies. Since this feature consists of two peaks (a main line and a shoulder on the low-energy side), this part of the spectrum was fitted with two components of Lorentzian line shapes. Results of the curve fit are given in Table 3.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.5 (a) Combined spectra from valence band photoemission (occupied energy states) and pre-peak in O K edge x-ray absorption spectra (unoccupied energy states) of Pr 0.67 Ca 0.33 MnO 3 taken at room temperature (above T c ). The three features corresponding to the subbands in the valence region are marked A, B, and C.The two peaks of the fitted O K edge pre-peak are marked A ′ and B ′ . We used integral background for both sides of E F . Details of the fitting are mentioned in the text. (b) Combined spectra of Pr 0.67 Ca 0.33 MnO 3 below T c . The valence band spectrum was taken at 77 K and O K edge XAS was taken at 95 K. . 70 3.6 Schematic diagram of the near-E F energy levels of Pr 0.67 Ca 0.33 MnO 3 in the occupied and unoccupied parts. The diagram is not drawn to scale. Some of the e g↑ states are occupied (at the Mn 3+ sites) and some are unoccupied (at the Mn 4+ sites). Hence the last occupied and first unoccupied states are marked with dotted lines. . . . . . . . . . . . . 71 4.1 Phase diagram of the Pr 1−x Ca x MnO 3 system. In this study we have used the x = 0.2, x = 0.33 and x = 0.4 compositions. (FMI = ferromagnetic insulating, CO-AFMI = charge ordered antiferromagnetic insulating, CG = cluster glass, T N = Neel Temperature, T C = Critical Temperature, T CO = charge ordering temperature). . . . . . . . . . . 79 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). . . . . . . . . . . 81 xxi
Page 1 and 2: SPECTROSCOPIC INVESTIGATIONS OF THE
Page 3 and 4: iii To My Parents
Page 5 and 6: Maharana, P. Khare, D. K. Basa, K.
Page 7 and 8: List of Publications/Preprints [1]
Page 9 and 10: Synopsis The perovskite type mangan
Page 11 and 12: to the t 2g and e g spin-up states
Page 13 and 14: Bibliography [1] R. von Helmolt, J.
Page 15 and 16: Contents CERTIFICATE Acknowledgemen
Page 17 and 18: List of Figures 1.1 Temperature dep
Page 19: 2.2 Schematic view of the energetic
Page 23 and 24: Chapter 1 Introduction 1
Page 25 and 26: Introduction 3 The temperature and
Page 27 and 28: Introduction 5 Figure 1.2: Schemati
Page 29 and 30: Introduction 7 Figure 1.4: A schema
Page 31 and 32: Introduction 9 Figure 1.6: Schemati
Page 33 and 34: Introduction 11 Figure 1.8: Differe
Page 35 and 36: Introduction 13 Figure 1.10: A sche
Page 37 and 38: Introduction 15 Figure 1.12: Schema
Page 39 and 40: Introduction 17 Figure 1.13: Phase
Page 41 and 42: Bibliography [1] R. von Helmolt, J.
Page 43 and 44: Introduction 21 [31] Damien Saurel,
Page 45 and 46: Chapter 2 Experimental Techniques 2
Page 47 and 48: Experimental Techniques 25 Figure 2
Page 49 and 50: Experimental Techniques 27 Let us n
Page 51 and 52: Experimental Techniques 29 and G(k,
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
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Experimental Techniques 49 Figure 2
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Bibliography [1] H. Hertz, Ann. Phy
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Experimental Techniques 57 [35] K.
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Chapter 3 Electronic Structure of P
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Electronic Structure of Pr 0.67 Ca
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Bibliography [1] I. G. Deac, J. F.
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Chapter 4 Electronic Structure of P
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Electronic Structure of Pr 1−x Ca
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Electronic Structure of Ca 0.86 Pr
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Bibliography [1] C. Zener, Phys. Re
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Summary and Conclusions 109 In this
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