Deterministic Magnetic Switching in Perpendicular Magnetic Trilayers Through Sunlight‐Induced Photoelectron Injection

Abstract

Finding an energy‐efficient way of switching magnetization is crucial in spintronic devices, such as memories. Usually, spins are manipulated by spin‐polarized currents or voltages in various ferromagnetic heterostructures; however, their energy consumption is relatively large. Here, a sunlight control of perpendicular magnetic anisotropy (PMA) in Pt (0.8 nm)/Co (0.65 nm)/Pt (2.5 nm)/PN Si heterojunction in an energy‐efficient manner is proposed. The coercive field (HC) is altered from 261 to 95 Oe (64% variation) under sunlight illumination, enabling a nearly 180° deterministic magnetization switching reversibly with a 140 Oe magnetic bias assistant. The element‐resolved X‐ray circular dichroism measurement reveals different L3 and L2 edge signals of the Co layer with or without sunlight, suggesting a photoelectron‐induced redistribution of the orbital and spin moment in Co magnetization. The first‐principle calculations also reveal that the photo‐induced electrons shift the Fermi level of electrons and enhance the in‐plane Rashba field around the Co/Pt interfaces, leading to a weakened PMA and corresponding HC decreasing and magnetization switching accordingly. The sunlight control of PMA may provide an alternative way for magnetic recording, which is energy efficient and would reduce the Joule heat from the high switching current.

Manipulations of Spin Waves by Photoelectrons in Ferromagnetic/Non‐Ferromagnetic Alloyed Film

“…According to the reported works, changes in the magnetic anisotropy and magnetization in the ferromagnetic layer originating from photoinduced electron doping can be quantified by in situ measurements of ESR and VSM. [35][36][37][38] The M-H loops of Co 60 Al 40 (2 nm)/PTB7-Th:PC 71 BM/Pt are illustrated in Figure 3a, where a decrease of 13.4% of M s in Co 60 Al 40 is obtained under sunlight irradiation. Figure 3b shows a zoom-in view around the coercive field (H c ), which drops from 24 to 20 Oe.…”

“…This results from band filling of Co film by photovoltaic electrons doping, leading to the depressed M s and H c accordingly, which has been discussed comprehensively in our previous works. [37,38] Figure 3ch shows the FMR spectra obtained by a test with a step of 1°. We conducted the in situ photovoltaic process on the Co 60 Al 40 film, and variations of FMR spectra can be observed by ESR under different light intensities, which is illustrated in Figure S6 (Supporting Information).…”

“…In this regard, inspired by the achievements of sunlight control over magnetism of ferromagnetic (FM) materials, [35][36][37][38] we obtained CoAl alloy thin films by the co-sputtering method and prepared a prototype photovoltaic tunable spin-wave device based on the Pt/PTB7-Th:PC 71 BM/Co 60 Al 40 /Ta/Si heterojunction, where PTB7-Th:PC 71 BM is used as the photovoltaic layer (PV) to produce photoelectrons. [39,40] We investigated the spindynamics behavior of the Co 60 Al 40 alloy through the angle dependence of the zero-order ferromagnetic resonance (FMR) spectrum.…”

Perspectives: Light Control of Magnetism and Device Development

“…These experimental results demonstrated the ability of visible light to control magnetization reversal in synthetic antiferromagnets and provide an important basis for the development of future spintronic memory and logic devices. Another heterostructure Pt/Co/Pt/PN Si was tested to verify the magnetization flip under sunlight irradiation by Zhao et al 214 They found a decreasing trend in the coercivity field under sunlight irradiation, making a deterministic magnetization flip of almost 180°possible. In addition, a nonvolatile magnetization flip was achieved by alternating sunlight and magnetic field bias, as shown in Figure 11f.…”

“…Deterministic magnetization strength switching process, change of I – V magnetic state, and periodic magnetization strength switching in the Pt/Co/Pt/PN Si heterostructure under bias field-assisted and sunlight control. Reprinted with permission from ref . Copyright 2023, Wiley-VCH GmbH.…”