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      Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel

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          Abstract

          High-harmonic spectroscopies reveal that fast energy transfer within 20 fs triggers ultrafast magnetic phase transition in Ni.

          Abstract

          It has long been known that ferromagnets undergo a phase transition from ferromagnetic to paramagnetic at the Curie temperature, associated with critical phenomena such as a divergence in the heat capacity. A ferromagnet can also be transiently demagnetized by heating it with an ultrafast laser pulse. However, to date, the connection between out-of-equilibrium and equilibrium phase transitions, or how fast the out-of-equilibrium phase transitions can proceed, was not known. By combining time- and angle-resolved photoemission with time-resolved transverse magneto-optical Kerr spectroscopies, we show that the same critical behavior also governs the ultrafast magnetic phase transition in nickel. This is evidenced by several observations. First, we observe a divergence of the transient heat capacity of the electron spin system preceding material demagnetization. Second, when the electron temperature is transiently driven above the Curie temperature, we observe an extremely rapid change in the material response: The spin system absorbs sufficient energy within the first 20 fs to subsequently proceed through the phase transition, whereas demagnetization and the collapse of the exchange splitting occur on much longer, fluence-independent time scales of ~176 fs. Third, we find that the transient electron temperature alone dictates the magnetic response. Our results are important because they connect the out-of-equilibrium material behavior to the strongly coupled equilibrium behavior and uncover a new time scale in the process of ultrafast demagnetization.

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          Most cited references46

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          Ultrafast Spin Dynamics in Ferromagnetic Nickel

          Physical Review Letters, 76(22), 4250-4253
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            Classics in Magnetics A Phenomenological Theory of Damping in Ferromagnetic Materials

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              Optical constants of transition metals: Ti, V, Cr, Mn, Fe, Co, Ni, and Pd

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                Author and article information

                Journal
                Sci Adv
                Sci Adv
                SciAdv
                advances
                Science Advances
                American Association for the Advancement of Science
                2375-2548
                March 2018
                02 March 2018
                : 4
                : 3
                : eaap9744
                Affiliations
                [1 ]Department of Physics and JILA, University of Colorado and National Institute of Standards and Technology (NIST), Boulder, CO 80309, USA.
                [2 ]NIST, 325 Broadway, Boulder, CO 80305, USA.
                [3 ]Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden.
                Author notes
                [*]

                These authors contributed equally to this work.

                []Corresponding author. Email: xun.shi@ 123456colorado.edu (X.S.); zhensheng.tao@ 123456jila.colorado.edu (Z.T.)
                Author information
                http://orcid.org/0000-0001-7794-1368
                http://orcid.org/0000-0003-0309-7656
                http://orcid.org/0000-0002-7091-9878
                http://orcid.org/0000-0001-8719-911X
                http://orcid.org/0000-0002-7806-9070
                http://orcid.org/0000-0002-3439-7638
                http://orcid.org/0000-0001-8573-2953
                http://orcid.org/0000-0002-9069-2631
                http://orcid.org/0000-0001-8386-6317
                http://orcid.org/0000-0003-1438-6074
                Article
                aap9744
                10.1126/sciadv.aap9744
                5834307
                29511738
                ddcb32ec-d9d0-41d1-a49e-804221729e8d
                Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

                History
                : 15 September 2017
                : 31 January 2018
                Funding
                Funded by: doi http://dx.doi.org/10.13039/100000001, National Science Foundation;
                Award ID: PHY-1125844
                Funded by: doi http://dx.doi.org/10.13039/100000015, U.S. Department of Energy;
                Award ID: DE-SC0002002
                Funded by: doi http://dx.doi.org/10.13039/100000936, Gordon and Betty Moore Foundation;
                Award ID: EPiQS Award GBMF4538
                Funded by: Swedish Research Council;
                Funded by: Wallenberg Foundation;
                Award ID: 2015.0060
                Categories
                Research Article
                Research Articles
                SciAdv r-articles
                Physics
                Custom metadata
                Jeanelle Ebreo

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