Ultrafast laser spectroscopy of half-metallic chromium dioxide.

摘要

This thesis presents ultrafast laser pump-probe differential transmission experiments on epitaxial CrO2 (110). The experiments were conducted at the wavelengths of 600 nm, 800 nm and 1200 nm, corresponding to the transition energies of 2 eV, 1.5 eV and 1 eV respectively. The wavelength dependent results, comparing with linear optical absorption, revealed the electronic structure of the material. The experimental results also showed polarization dependence of the probe beams. This is attributed to the electronic orbital anisotropy.; Temperature dependence was observed in the pump-probe experiments. The ultrafast transmission data show similar temperature dependence as ultrafast MOKE (Magneto-Optical Kerr Effect) data. A critical change of transient transmission was observed at the Curie temperature of 386 K. Spin decay processes are discussed based on these temperature dependent time resolved data.; Ultrafast MOKE experiments are also presented. Oscillations of the time resolved MOKE signal corresponding to the ferromagnetic resonance were observed. The magnetic anisotropies of the CrO2 thin film were studied by analyzing these oscillations. A computer program was developed for data analysis.; A general discussion of the relation between magnetic properties and the electronic properties of the material is delivered.