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Register a new userExchange dependent ultrafast magnetization dynamics in Fe$_{1-x}$Ni$_{x}$ alloys
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Somnath Jana
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Element specific ultrafast demagnetization was studied in Fe$_{1-x}$Ni$_{x}$ alloys, covering the concentration range between $0.1<x<0.9$. For all compositions, we observe a delay in the onset of Ni demagnetization relative to the Fe demagnetization. We find that the delay is correlated to the Curie temperature and hence also the exchange interaction. The temporal evolution of demagnetization is fitted to a magnon diffusion model based on the presupposition of enhanced ultrafast magnon generation in the Fe sublattice. The spin wave stiffness extracted from this model correspond well to known experimental values.
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In this paper, high Fe-concentration Fe$_{1-x}$Ni$_{x}$ alloys were investigated using high resolution X-ray photoelectron spectroscopy (XPS) down to 10K temperature. The Fe 2s core level exhibits three features, two low binding features corresponding to exchange interaction between ionized 2s core level and the unpaired 3d electrons. The high binding energy feature corresponds to the screening of 2s core hole by 4s conduction electrons. Our studies suggest high local magnetic moments on Fe sites.
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Recent investigations have advanced the understanding of how structure-property relationships in ferromagnetic metal alloys affect the magnetization dynamics on nanosecond time-scales. A similar understanding for magnetization dynamics on femto- to pico-second time-scales does not yet exist. To address this, we perform time-resolved magneto optic Kerr effect (TRMOKE) measurements of magnetization dynamics in Co-Fe alloys on femto- to nano-second regimes. We show that Co-Fe compositions that exhibit low Gilbert damping parameters also feature prolonged ultrafast demagnetization upon photoexcitation. We analyze our experimental TR-MOKE data with the three-temperature-model (3TM) and the Landau-Lifshitz-Gilbert equation. These analyses reveal a strong compositional dependence of the dynamics across all time-scales on the strength of electron-phonon interactions. Our findings are beneficial to the spintronics and magnonics community, and will aid in the quest for energy-efficient magnetic storage applications.
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