Title: Correlation between Spin and Orbital Dynamics during Laser-Induced Femtosecond Demagnetization

Abstract

Spin and orbital angular momenta are two intrinsic properties of an electron and are responsible for the physics of a solid. How the spin and orbital evolve with respect to each other on several hundred femtoseconds is largely unknown, but it is at the center of laser-induced ultrafast demagnetization. In this paper, we introduce a concept of the spin–orbital correlation diagram, where spin angular momentum is plotted against orbital angular momentum, much like the position-velocity phase diagram in classical mechanics. We use four sets of highly accurate time-resolved X-ray magnetic circular dichroism data to construct four correlation diagrams for iron and cobalt. To our surprise, a pattern emerges. The trace on the correlation diagram for iron is an arc, and at the end of demagnetization, it has a pronounced cusp. The correlation diagram for cobalt is different and appears more linear but with kinks. We carry out first-principles calculations with two different methods: time-dependent density functional theory (TDDFT) and time-dependent Liouville density functional theory. These two methods agree that the experimental findings for both Fe and Co are not due to experimental errors. It is the spin–orbit coupling that correlates the spin dynamics to the orbital dynamics. Microscopically, Fe andmore » Co have different orbital occupations, which leads to distinctive correlation diagrams. We believe that this correlation diagram presents a useful tool to better understand spin and orbital dynamics on an ultrafast time scale. A brief discussion on the magnetic anisotropy energy is also provided.« less

Authors:

Zhang, G. P.  ^[1];

• Search DOE PAGES for author "Zhang, G. P."
• Search DOE PAGES for ORCID "0000-0002-1792-2701"

Gu, Mingqiang ^[2]; Bai, Y. H. ^[1]; Jenkins, T. L. ^[1]; George, Thomas F.  ^[3]

• Search DOE PAGES for author "George, Thomas F."
• Search DOE PAGES for ORCID "0000-0003-1225-6778"

---

+ Show Author Affiliations

1. Indiana State Univ., Terre Haute, IN (United States)
2. Southern Univ. of Science and Technology, Shenzhen (China)
3. Univ. of Missouri, St. Louis, MO (United States)

Publication Date:

Thu Jun 24 00:00:00 EDT 2021

Research Org.:

Indiana State Univ., Terre Haute, IN (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1830717

Grant/Contract Number:  

FG02-06ER46304; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 125; Journal Issue: 26; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Time dependant density functional theory; Energy; Quantum mechanics; Theoretical and computational chemistry; Lasers