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      Band-Structure-Dependent Demagnetization in the Heusler Alloy\({\mathrm{Co}}_{2}{\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_{x}\mathrm{Si}\)

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          Abstract

          We investigate the ultrafast demagnetization for two Heusler alloys (Co₂Mn(1-x)FexSi) with a different lineup of the minority band gap and the Fermi level. Even though electronic spin-flip transitions are partially blocked by the band gap in one compound, the respective magnetization dynamics, as measured by the time-resolved Kerr effect, are remarkably similar. Based on a dynamical model that includes momentum and spin-dependent carrier scattering, we show that the magnetization dynamics are dominated by hole spin-flip processes, which are not influenced by the gap.

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          Most cited references 21

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          Ultrafast spin dynamics in ferromagnetic nickel.

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            Explaining the paradoxical diversity of ultrafast laser-induced demagnetization.

            Pulsed-laser-induced quenching of ferromagnetic order has intrigued researchers since pioneering works in the 1990s. It was reported that demagnetization in gadolinium proceeds within 100 ps, but three orders of magnitude faster in ferromagnetic transition metals such as nickel. Here we show that a model based on electron-phonon-mediated spin-flip scattering explains both timescales on equal footing. Our interpretation is supported by ab initio estimates of the spin-flip scattering probability, and experimental fluence dependencies are shown to agree perfectly with predictions. A phase diagram is constructed in which two classes of laser-induced magnetization dynamics can be distinguished, where the ratio of the Curie temperature to the atomic magnetic moment turns out to have a crucial role. We conclude that the ultrafast magnetization dynamics can be well described disregarding highly excited electronic states, merely considering the thermalized electron system.
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              Femtosecond modification of electron localization and transfer of angular momentum in nickel.

              The rapidly increasing information density required of modern magnetic data storage devices raises the question of the fundamental limits in bit size and writing speed. At present, the magnetization reversal of a bit can occur as quickly as 200 ps (ref. 1). A fundamental limit has been explored by using intense magnetic-field pulses of 2 ps duration leading to a non-deterministic magnetization reversal. For this process, dissipation of spin angular momentum to other degrees of freedom on an ultrafast timescale is crucial. An even faster regime down to 100 fs or below might be reached by non-thermal control of magnetization with femtosecond laser radiation. Here, we show that an efficient novel channel for angular momentum dissipation to the lattice can be opened by femtosecond laser excitation of a ferromagnet. For the first time, the quenching of spin angular momentum and its transfer to the lattice with a time constant of 120+/-70 fs is determined unambiguously with X-ray magnetic circular dichroism. We report the first femtosecond time-resolved X-ray absorption spectroscopy data over an entire absorption edge, which are consistent with an unexpected increase in valence-electron localization during the first 120+/-50 fs, possibly providing the driving force behind femtosecond spin-lattice relaxation.
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                Author and article information

                Journal
                PRLTAO
                Physical Review Letters
                Phys. Rev. Lett.
                American Physical Society (APS)
                0031-9007
                1079-7114
                November 2010
                November 15 2010
                : 105
                : 21
                Article
                10.1103/PhysRevLett.105.217202
                21231346
                © 2010

                http://link.aps.org/licenses/aps-default-license

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