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Title: Laser-induced ultrafast demagnetization time and spin moment in ferromagnets: First-principles calculation

When a laser pulse excites a ferromagnet, its spin undergoes a dramatic change. The initial demagnetization process is very fast. Experimentally, it is found that the demagnetization time is related to the spin moment in the sample. In this study, we employ the first-principles method to directly simulate such a process. We use the fixed spin moment method to change the spin moment in ferromagnetic nickel, and then we employ the Liouville equation to couple the laser pulse to the system. We find that in general the dependence of demagnetization time on the spin moment is nonlinear: It decreases with the spin moment up to a point, after which an increase with the spin moment is observed, followed by a second decrease. To understand this, we employ an extended Heisenberg model, which includes both the exchange interaction and spin-orbit coupling. The model directly links the demagnetization rate to the spin moment itself and demonstrates analytically that the spin relaxes more slowly with a small spin moment. A future experimental test of our predictions is needed.
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States)
  2. Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)
  3. Office of the Chancellor and Center for Nanoscience, Departments of Chemistry and Biochemistry and Physics and Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121 (United States)
Publication Date:
OSTI Identifier:
22410093
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 17; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BOLTZMANN-VLASOV EQUATION; COMPUTERIZED SIMULATION; DEMAGNETIZATION; EXCHANGE INTERACTIONS; FERROMAGNETIC MATERIALS; HEISENBERG MODEL; LASER RADIATION; L-S COUPLING; MOMENTS METHOD; NICKEL; NONLINEAR PROBLEMS; PULSED IRRADIATION; SPIN