臺灣博碩士論文加值系統

以時間解析反射率和時間解析磁光效應量測系統可量測鑭鈣錳氧(La0.7Ca0.3MnO3)載子和自旋的動態行為。在這一系列的實驗中我們直接觀測到不同溫度和不同磁場下載子和自旋的暫態行為。在這類巨磁阻材料中，自旋的生命期是快於載子的生命期。自旋的弛裕過程是經由複雜的自旋、電子和晶格的熱平衡。在臨界溫度以下，自旋經過快速的弛裕以後，暫態的磁光效應訊號將與激發光的極化無關。這一訊號是由於自旋－電子的交互作用而來的，它導致晶格暫時的冷卻現象。

The time-resolved photoreflectance and MOKE measurement systems are used to measure the carrier and spin dynamics of La0.7Ca0.3MnO3, a typical colossal magnetoresistance material (CMR). We have directly observed the transient behaviors of carrier and spin at different temperature and under differently external fields. They are evidenced that the spin relaxation time is faster than carrier relaxation time in this material. The relaxation processes of the spin are due to complex thermal equilibrium among the spin, electron, and lattice. The transient MOKE trace, which is independent of pumped polarization after the fastest relaxation time of spin at low temperature < Tc, will cool down the lattice temperature due to electron-spin interactions.

Chapter 1: Overview of Colossal Magnetoresistance and Ultrafast Magneto-optical measurements
1.1 Introduction to colossal magnetoresistance(CMR)—La1-xCaxMnO3 1
1.2 Introduction to ultrafast magneto-optical experiment 6
1.3 Introduction to magneto-optical effect 9
1.3.1 Optical transmission 9
1.3.2 Optical reflection 10
Chapter 2: Experimental Setup and Sample Preparation
2.1 Low Temperature Ultra-fast MOKE Measurement System Setup 14
2.2 The pulse-width measurement 19
2.3 Sample Preparation 20
Chapter 3: Ultrafast properties of La0.7Ca0.3MnO3
3.1 The transient photoreflectance measurements 24
3.2 The dc MOKE measurement 29
3.3 The time-resolved MOKE measurement 31
3.4 Discussions 41
Chapter 4: Conclusion 53
References 58
APPENDIX
Appendix A 58
Appendix B 59

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