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

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 connectmore » the out-of-equilibrium material behavior to the strongly coupled equilibrium behavior and uncover a new time scale in the process of ultrafast demagnetization.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [1]; ORCiD logo [1];  [1]
  1. University of Colorado and National Institute of Standards and Technology (NIST), Boulder, CO (United States)
  2. National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
  3. Uppsala Univ. (Sweden)
Publication Date:
Research Org.:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1499934
Grant/Contract Number:  
SC0002002
Resource Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 4; Journal Issue: 3; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Tengdin, Phoebe, You, Wenjing, Chen, Cong, Shi, Xun, Zusin, Dmitriy, Zhang, Yingchao, Gentry, Christian, Blonsky, Adam, Keller, Mark, Oppeneer, Peter M., Kapteyn, Henry C., Tao, Zhensheng, and Murnane, Margaret M. Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel. United States: N. p., 2018. Web. doi:10.1126/sciadv.aap9744.
Tengdin, Phoebe, You, Wenjing, Chen, Cong, Shi, Xun, Zusin, Dmitriy, Zhang, Yingchao, Gentry, Christian, Blonsky, Adam, Keller, Mark, Oppeneer, Peter M., Kapteyn, Henry C., Tao, Zhensheng, & Murnane, Margaret M. Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel. United States. doi:10.1126/sciadv.aap9744.
Tengdin, Phoebe, You, Wenjing, Chen, Cong, Shi, Xun, Zusin, Dmitriy, Zhang, Yingchao, Gentry, Christian, Blonsky, Adam, Keller, Mark, Oppeneer, Peter M., Kapteyn, Henry C., Tao, Zhensheng, and Murnane, Margaret M. Fri . "Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel". United States. doi:10.1126/sciadv.aap9744. https://www.osti.gov/servlets/purl/1499934.
@article{osti_1499934,
title = {Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel},
author = {Tengdin, Phoebe and You, Wenjing and Chen, Cong and Shi, Xun and Zusin, Dmitriy and Zhang, Yingchao and Gentry, Christian and Blonsky, Adam and Keller, Mark and Oppeneer, Peter M. and Kapteyn, Henry C. and Tao, Zhensheng and Murnane, Margaret M.},
abstractNote = {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.},
doi = {10.1126/sciadv.aap9744},
journal = {Science Advances},
number = 3,
volume = 4,
place = {United States},
year = {2018},
month = {3}
}

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Cited by: 21 works
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Figures / Tables:

Fig. 1. Fig. 1.: Schematic of the critical behavior of ultrafast demagnetization in Ni. (A) After excitation by a femtosecond laser pulse above the critical fluence (Fc), the transient electron temperature (Te) is driven above the Curie temperature (Tc), inducing high-energy spin excitations within 20 fs, which store the magnetic energy (seemore » text). The Fermi-Dirac distributions of electrons are also plotted. Demagnetization occurs later, in ~176 fs, driven by relaxation of nonequilibrium spins and the likely excitation of low-energy magnons. Full recovery of the spin system occurs within ~500 fs to ~76 ps, depending on the laser fluence. (B and C) Experimental setups for time-resolved ARPES and TMOKE, respectively, using ultrafast high-harmonic sources. IR, infrared.« less

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    Works referencing / citing this record:

    Generation of extreme-ultraviolet beams with time-varying orbital angular momentum
    journal, June 2019


      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.