First-principles and model simulation of all-optical spin reversal

Zhang, G. P.; Babyak, Z.; Xue, Yuxiong; Bai, Yihua; George, Thomas F.

doi:10.1103/physrevb.96.134407

Cited by 18 publications

(31 citation statements)

References 49 publications

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“…If we compare σ + and σ − , we find their final spins lie opposite to each other. This strong helicity dependence is consistent with our prior model study [45]. It is possible that our model does not include the itinerancy of the electrons sufficiently, so the helicity dependence is stronger from our model.…”

Section: A Dependence Of Demagnetization On System and Laser Parameterssupporting

confidence: 89%

“…Once we initialize the spin along the −z axis, σ + and σ − are no longer equivalent because the spin determines the quantization axis. Figure 2 [45]. Once the spin points down, its effect is small.…”

Section: A Dependence Of Demagnetization On System and Laser Parametersmentioning

confidence: 97%

“…It is possible that our model does not include the itinerancy of the electrons sufficiently, so the helicity dependence is stronger from our model. A weak helicity dependence is obtained using the first-principles method [45]. Figure 2 The helicity is not the only one that affects the spin.…”

Section: A Dependence Of Demagnetization On System and Laser Parametersmentioning

confidence: 99%

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Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism

Zhang

Murakami

Bai

et al. 2019

Journal of Applied Physics

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Laser-induced femtosecond demagnetization, femtomagnetism, offers a potential route to develop faster magnetic storage devices. It is generally believed that the traditional spin-wave theory, which is developed for thermally driven slow demagnetization, can not explain this rapid demagnetization by design. Here we show that this traditional spin-wave theory, once augmented by laser-induced spin-orbit torque, provides a highly efficient paradigm for demagnetization, by capturing lowenergy spin-wave excitation that is absent in existing mechanisms. Our paradigm is different from existing ones, but does not exclude them. Microscopically, we find that optical spin-orbit torque generates massive spin waves across several hundred lattice sites, collapsing the long-range spin-spin correlation within 20 fs. Our finding does not only explain new experiments, but also establishes an alternative paradigm for femtomagnetism. It is expected to have far-reaching impacts on future research.

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Section: A Dependence Of Demagnetization On System and Laser Parameterssupporting

confidence: 89%

Section: A Dependence Of Demagnetization On System and Laser Parametersmentioning

confidence: 97%

See 1 more Smart Citation

Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism

Zhang

Murakami

Bai

et al. 2019

Journal of Applied Physics

Self Cite

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“…We recently showed that when one has a ferrimagnet [14], care must be taken because two different helicities act upon two respective sets of spins, leading to apparent HID switching.…”

Section: Introductionmentioning

confidence: 99%

“…Because optical selection rules depend on the spatial orientation of spins in a domain [14][15][16], even subject to the same laser beam, spins inside the domain wall behave differently.…”

Section: Introductionmentioning

confidence: 99%

All-optical spin switching under different spin configurations

Zhang¹,

Murakami²

2019

J. Phys.: Condens. Matter

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All-optical spin switching represents a new frontier in femtomagnetism. However, its underlying principles are quite different from traditional thermal activated spin switching. Here, we employ an atomic spin model and present a systematic investigation from a single spin to a large system of over a million spins. We find that for a single spin without an external perturbation, the conservation of total angular momentum requires that the spin change, if any, exactly matches the orbital momentum change, but a laser pulse significantly alters this relation, where the spin change does not necessarily follow the orbital change. This is reflected in the strong dependence of switching on laser polarization. To have an efficient spin switching, the electron initial momentum direction must closely follow the spin's orientation, so the orbital angular momentum is transverse to the spin and consequently the spin-orbit torque lies in the same direction as the spin. The module of the spin-orbit torque is λ|S||r||P| cos 2 α + cos 2 β − 2 cos α cos β cos γ, where α(β) is the angle between spin S and position r(momentum P) and γ is the angle between r and P. These findings are manifested in a much larger system. We find that the spin response depends on underlying spin structures. A linearly polarized laser pulse creates a dip in a uniform inplane-magnetized thin film, but has little effects on Néel and Bloch walls. Both right-and left-circularly polarized light (σ + and σ − ) have stronger but different effects in both uniform spin domains and Néel walls. While σ + light creates a basin of spins pointing down, σ − light creates a mound of spins pointing up. In the vicinity of the structure spins are reversed, similar to the experimental observation. σ + light has a dramatic effect, disrupting spins in Bloch walls. By contrast, σ − light has a small effect on Bloch walls because σ − only switches down spins up and once the spins already point up, there is no major effect. These findings are expected to have important implications in the future.

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Timescales and contribution of heating and helicity effect in helicity-dependent all-optical switching

Zheng²,

Wang³

et al. 2022

Rare Met.

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The heating and helicity effects induced by circularly polarized laser excitation are entangled in the helicity-dependent all-optical switching (HD-AOS), which hinders understanding the magnetization dynamics involved. Here, applying a dual-pump laser excitation, first with a linearly polarized (LP) laser pulse followed by a circularly polarized (CP) laser pulse, the timescales and contribution from heating and helicity effects in HD-AOS were identified with a Pt/Co/Pt triple-layer. When the LP laser pulses preheat the sample to a nearly fully demagnetized state, the CP laser pulses with a power reduced by 80% switch the sample’s magnetization. By varying the time delay between the two pump pulses, the results show that the helicity effect, which gives rise to the deterministic helicity-induced switching, arises almost instantly within 200 fs close to the pulse width upon laser excitation. The results reveal that the transient magnetization state upon which CP laser pulses impinge is the key factor for achieving HD-AOS, and importantly, the tunability between heating and helicity effects with the unique dual-pump laser excitation approach will enable HD-AOS in a wide range of magnetic material systems having wide-ranging implications for potential ultrafast spintronics applications. Graphical abstract

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First-principles and model simulation of all-optical spin reversal

Cited by 18 publications

References 49 publications

Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism

Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism

All-optical spin switching under different spin configurations

Timescales and contribution of heating and helicity effect in helicity-dependent all-optical switching

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