Abstract
Ultrafast laser-induced magnetization dynamics in ferromagnetic thin films were measured using a femtosecond Ti:sapphire laser in a pump-probe magneto-optic Kerr effect setup. The effect of plasmon resonance on the transient magnetization was investigated by drop-coating the ferromagnetic films with dimensionally-tuned gold nanorods supporting longitudinal surface plasmon resonance near the central wavelength of the pump laser. With ~4% nanorod areal coverage, we observe a >50% increase in demagnetization signal in nanorod-coated samples at pump fluences on the order of 0.1 mJ/cm2 due to surface plasmon-mediated localized electric-field enhancement, an effect which becomes more significant at higher laser fluences. We were able to qualitatively reproduce the experimental observations using finite-difference time-domain simulations and mean-field theory. This dramatic enhancement of ultrafast laser-induced demagnetization points to possible applications of nanorod-coated thin films in heat-assisted magnetic recording.
Highlights
A ferromagnetic (FM) thin film excited by femtosecond pulsed laser will undergo ultrafast loss of magnetic order within several hundred femtoseconds, due to rapid energy transfer from thermalized electrons to the spin system
We investigate the improvement in laser-induced demagnetization signal through localized surface plasmons (LSPs)-enhanced localized heating
By coating FM thin films with gold nanorods (AuNRs)
Summary
Haitian Xu1, Ghazal Hajisalem[2], Geoffrey M. The effect of plasmon resonance on the transient magnetization was investigated by drop-coating the ferromagnetic films with dimensionally-tuned gold nanorods supporting longitudinal surface plasmon resonance near the central wavelength of the pump laser. With ~4% nanorod areal coverage, we observe a >50% increase in demagnetization signal in nanorod-coated samples at pump fluences on the order of 0.1 mJ/cm[2] due to surface plasmon-mediated localized electric-field enhancement, an effect which becomes more significant at higher laser fluences. We were able to qualitatively reproduce the experimental observations using finite-difference time-domain simulations and mean-field theory This dramatic enhancement of ultrafast laser-induced demagnetization points to possible applications of nanorod-coated thin films in heat-assisted magnetic recording. A ferromagnetic (FM) thin film excited by femtosecond pulsed laser will undergo ultrafast loss of magnetic order (demagnetization) within several hundred femtoseconds, due to rapid energy transfer from thermalized electrons to the spin system. The AuNR coating functions in a similar capacity to NP transducers in HAMR recording heads, and the arrangement offers a possible solution to the thermal degradation problem in current HAMR prototypes by uniformly distributing or patterning the plasmon NPs across the surface of the recording medium, subjecting individual AuNRs to a small fraction of the overall thermal cycling
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