Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session N21: Magnons, Magnonics, and Magnetization Dynamics
11:30 AM–2:30 PM,
Wednesday, March 6, 2024
Room: 101A
Sponsoring
Unit:
GMAG
Chair: Branislav Nikolic, University of Delaware; Dali Sun, North Carolina State University, Physics Department
Abstract: N21.00003 : Enhancing Spin Torque Optical Readout with Sagnac Interferometry*
12:18 PM–12:30 PM
Presenter:
Orion Smedley
(Cornell University)
Authors:
Orion Smedley
(Cornell University)
Thow Min Jerald Cham
(Cornell University)
Saba Karimeddiny
(Cornell University)
Alicia Wallace
(Smith)
Daniel C Ralph
(Cornell University)
Kelly Luo
(Cornell University)
In this study, we analyze the Sagnac signal to second order in the magnetization. We demonstrate an additional advantage of Sagnac interferometry: it effectively suppresses the quadratic Kerr effect. Conventional MOKE produces an angular readout defined by θconventional = κ mz + β mx my , where β represents the quadratic coefficient, κ represents the linear coefficient, and m = [mx,my,mz] represents the magnetization vector. In comparison, the SAGNAC interferometer signal is
θsagnac ≈ κ mz + 2 β mx my sin(κ mz) [0.71cos(2 κ mz) - 0.62 cos2(κ mz)] + O(β2)
Notably, the quadratic term is smaller than the linear term by a factor of β (order 10−4) , rather than β/κ. Furthermore, a small modification to the interferometer reverses this suppression, to isolate the quadratic effect. Because the quadratic MOKE provides information about two other components of magnetism, this could enable fully vectorial measurements of spin torques.
*Funding: NSF DMR-2104268
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