Tomasz Błachowicz

Brillouin Spectroscopy in Crystal Lattices. Acoustic and Spin Waves

Silesian University of Technology Press, Gliwice 2003, PL ISSN 0072-470X

Table of contents

Foreword	7
1. Introduction	13
2. Theory of the Brillouin light scattering on phonons	20
2.1 Light scattering on bulk acoustic phonons	20
2.1.1 Influence of rotational contributions to scattering phenomenon	25
2.1.2 Scattering on the two phonon branches - the switching phenomenon	44
2.1.3 Coherent states approach	47
2.1.4 Scattering configurations for transparent crystals	54
2.2 Acoustic phonons in thin layers and multilayered structures	56
2.2.1 Scattering cross-section in a semi-infinite medium	56
2.2.2 Theory of acoustic modes in bilayered structures - the isotropic, cubic and hexagonal problems	66
2.2.2.1 Boundary conditions at the interface	77
2.2.2.2 The cubic layer on the hexagonal substrate	80
3. Experimental setup for Brillouin light scattering	84
3.1 Introduction	84
3.2 Geometries of light scattering in the BLS experiments	85
3.3 Scanning the interferometry	87
3.3.1 Pressure scanning theory	88
3.3.2 Pressure scanning construction details	91
3.3.3 Piezoelectric scanning construction details	94
3.4 Sources of experimental errors for a pressure scanned system and bulk geometry of scattering	99
3.5 Sources of experimental errors in a back-scattering geometry	102
3.6 Single photon counting	109
3.7 Reading of noised spectra using wavelet analysis	114
3.8 Extracting a half-width of spectral lines using deconvolution technique	128
4. Bulk-type results of measurements in the LiNbO3, SLAO, and SLGO crystals	134
4.1 Experiment with the LiNbO3 crystal	134
4.1.1 Analysis of spectra with lines of large intensities	135
4.1.2 Switching of a scattering channel between acoustic phonons branches	139
4.1.3 Influence of doping process on acoustic phonons frequency in the LiNbO3:Cu crystal	144
4.2 Derivation of elastic constants for the SLAO and SLGO crystals	147
4.2.1 Brillouin scattering results	147
4.2.2 Ultrasonic experiment - the pulse-echo method	149
4.2.3 Wide-frequency background in the BLS spectrum from SLAO crystal	153
5. Results of measurements in the Co/Cu superlattices and the Co/CoO bilayers	162
5.1 Brillouin light scattering in multilayered structures	162
5.2 Acoustic waves in multilayered superlattices	164
5.2.1 Experiments with acoustic waves in the Co/Cu superlattices	171
5.3 Spin waves in multilayered superlattices	179
5.3.1 Experiments with spin waves in the Co/Cu multilayered superlattices	188
5.3.2 Experiments with spin waves in the Co/CoO exchange-bias samples	201
5.3.3 Unresolved problem of the anomalous Brillouin line-width broadening in exchange-bias samples	214
6. Conclusions and outlook	217
Appendix A - MOKE measurements	221
Appendix B - Electron and optical microscopy measurements	228
Appendix C - SQUID measurements	243
References	246
Basic symbols	268
Index	272
Summary	275