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20 December 2019 The nature of non-equilibrium ultrafast demagnetization in ferromagnetic nickel
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Proceedings Volume 11209, Eleventh International Conference on Information Optics and Photonics (CIOP 2019); 1120938 (2019) https://doi.org/10.1117/12.2548814
Event: Eleventh International Conference on Information Optics and Photonics (CIOP 2019), 2019, Xi'an, China
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-ofequilibrium and equilibrium phase transitions was not known, nor how fast the out-of-equilibrium phase transitions can proceed. In this work, by combining time- and angle-resolved photoemission (Tr-ARPES) with time-resolved transverse magneto-optical Kerr (Tr-TMOKE) 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, while demagnetization and the collapse of the exchange splitting occur on much longer timescales. Third, we find that the transient electron temperature alone dictates the magnetic response. By comparing results obtained from different methods, we show that the critical behaviors are essential for fully explaining the fluence-dependent magnetization dynamics measured using magneto-optical spectroscopy
© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Zhensheng Tao, Phoebe Tengdin, Wenjing You, Cong Chen, Xun Shi, Dmitriy Zusin, Yingchao Zhang, Christian Gentry, Adam Blonsky, Mark Keller, Peter M. Oppeneer, Henry C. Kapteyn, and Margaret M. Murnane "The nature of non-equilibrium ultrafast demagnetization in ferromagnetic nickel", Proc. SPIE 11209, Eleventh International Conference on Information Optics and Photonics (CIOP 2019), 1120938 (20 December 2019); https://doi.org/10.1117/12.2548814
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