Dissertation
Dissertation > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > The nature of the films > Magnetic properties

FePt / CoFe magnetic composite membrane dynamics of laser pump-probe

Author CuiBoYin
Tutor JinQingYuan
School Fudan University
Course Optics
Keywords Spin dynamics Ultrafast Spin- wave excitation Magnetization Magnetically ordered Magneto-optical Kerr effect Precession FePt / CoFe Pump - probe technique Magnetosphere Damping Factor Pump-probe External magnetic field Magnetic anisotropy Outfield Laser pumping Easy magnetization direction Exchange coupling Femtosecond laser pulses Annealing time
CLC O484.43
Type Master's thesis
Year 2011
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The interaction of subpicosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of subpicosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, manipulation of magnetic order by ultrashort laser pulses is of significant importance for basic research and practical applications in magnetic storage.In this paper, we have investigated the ultrafast spin precession and decay process of FePt/CoFe exchange-coupled composite materials by time-resolved magnetic optical Kerr effect (TRMOKE). The first chapter introduces the background of ultrafast optical manipulation of magnetic order. The second chapter describes the experimental techniques for thin film deposition and pump-probe technique. The third chapter demonstrates the static magnetic properties of FePt/CoFe composite films. The fourth chapter shows their magnetic dynaimc properties, we found that the easy magnetization direction of the FePt/CoFe sample is related to the substrate temperature during FePt growth and the thickness of CoFe layer, which is a key factor to affect the demagnetization and magnetic recovery process after laser heating. Summary and propects are given in the last chapter.The laser-induced spin dynamics in the FePt/CoFe films has been studied by the longitudinal time-resolved magneto-optical Kerr effec. Two different substrate temperatures of Ts=380 and 425 degrees were used to acquire the hard magnetic FePt phase. By varying the structure of the samples and measurement conditions (soft layer thickness, the external field, the intensity of the pump beam, the annealing of FePt layer), we obtain the demagnetization and the subsequent magnetization relaxation process. Some samples display a decayed precession behavior under proper conditions. The observed precession frequency, which is not affected by the pump laser intensity and CoFe thickness, displays a linear relationship to the magnitude of external field. The amplitude of the precession varies with the CoFe thickness and the external field. Analyses show that the magnetization relaxation in this FePt/CoFe system is governed by a uniform precession mode. The result agrees well with the theoretical prediction based on the Landau-Lifshitz-Gilbert equation. The obtained damping factor a-0.13 is quite large and is thought to originate from the FePt layer due to its large spin-orbit interaction.

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