Study Of Ultrafast Spin Dynamics Induced By Polarized Light On Magnetic Thin Films

In this thesis,a time-resolved magneto-optical Kerr system based on femtosecond laser pulses was employed to study the spin dynamics on multilayer magnetic films[Pt/Co]_N/Mn Ir and multiferroic thin films Pr_1-xCa_xMn O₃pumped by light with different helicity.The main research contents are as follows:(1)First,It was found that there was a transient Kerr signal besides the demagnetization process in the MOKE signal when[Pt/Co]_N/Mn Ir multilayer ferromagnetic films were pumped by 800nm left and right circularly polarized light.The direction of transient Kerr peak only depends on the angular momentum direction.We also found that the pulse width of transient Kerr peak is equivalent to the pulse width of autocorrelation peak.Then we conducted a series of experiments to explore the contribution made by Mn Ir and Co to the amplitude of transient Kerr peak.It is found that the transient Kerr peak originates from the magnetization of paramagnetic electrons.Finally,we found that it is the mechanism and period of SIFE and SOKE that make the amplitude of the transient Kerr peak present an approximate shape of sine as a function of?.(2)Employing the time-resolved magneto-optical Kerr system,we changed the output power of pump light and found that the amplitudes of the transient Kerr peaks increased with the pump power increasing.This was because the magnetic field generated by the inverse Faraday effect will increase when the energy density increases.Secondly,it is found that under different doping ratios,the amplitudes of transient Kerr signal were different when PCMO was pumped by circularly polarized light carrying on different angular momentum.This is because that Magneto optical coefficient is a third-order nonlinear elastic coefficient tensor,which is related to both the material itself and magnetization.