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# Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co88Tb12 thin film with stripe domains

Marcel Hennes, Alaa El Dine Merhe, Xuan Liu, David Weder, Clemens von Korff Schmising, Michael Schneider, Christian Michael Günther, Benoît Mahieu, Grégory Malinowski, Michel Hehn, et al.

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## ► To cite this version:

Marcel Hennes, Alaa El Dine Merhe, Xuan Liu, David Weder, Clemens von Korff Schmising, et al. Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co88Tb12 thin film with stripe domains. Ultrafast Magnetic Conference, Sep 2022, Nancy, France. 2022. [hal-03974509](https://hal.science/hal-03974509)

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https://hal.science/hal-03974509

Submitted on 5 Feb 2023

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# Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co<sub>88</sub>Tb<sub>12</sub> thin film with stripe domains

¹M. Hennes, ¹A. Merhe, ¹X. Liu, ²D. Weder, ²C. von Korff Schmising, ²M. Schneider, ³C. M. Günther, ⁴B. Mahieu, ⁵G. Malinowski, ⁵M. Hehn, ⁵D. Lacour, ⁶F. Capotondi, ⁶E. Pedersoli, ⁶I. P. Nikolov, ¹V. Chardonnet, ¹E. Jal, ¹J. Lüning and ¹B. Vodungbo

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SCIENCES
SORBONNE
UNIVERSITÉ

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## Abstract

We use time-resolved x-ray resonant magnetic scattering (TR-XRMS) at the Co M<sub>2,3</sub> and Tb O<sub>1</sub> edges to study ultrafast demagnetization in an amorphous Co<sub>88</sub>Tb<sub>12</sub> alloy with stripe domains. Combining the femtosecond temporal with nanometer spatial resolution of our experiment, we demonstrate that the equilibrium spin texture of the thin film remains unaltered by the optical pump pulse on ultrashort timescales (< 1 ps). However, after 4 ps, we observe the onset of a significant domain wall broadening, which we attribute to a reduction of the uniaxial magnetic anisotropy of the system, due to energy transfer to the lattice. Static temperature-dependent magnetometry measurements combined with analytical modeling of the magnetic structure of the thin film corroborate this interpretation.

<figure><img src="image_6.png" /><figcaption>### X-ray resonant magnetic scattering [1]</figcaption></figure>

Experiment realized at FERMI free electrons laser
Co<sub>88</sub>Tb<sub>12</sub> sample presenting a stripe domains structure
Observing intensity of scattering orders (1st and 3rd) as a function of time delay

<figure><img src="image_7.png" /><figcaption>### Azimuthal integration of scattering pattern (along θ)</figcaption></figure>

1st and 3rd peaks remain fixed as function of time
No modification of the domain structure periodicity

## Scattering intensity as function of time delay

<figure><img src="image_8.png" /></figure>

1st and 3rd orders intensity have very different dynamics
This reveals a modification of the domain wall region

<figure><img src="image_9.png" /><figcaption>### Fit to domain wall model [2]</figcaption></figure>

Magnetic domain structure describe with linear domain wall

<figure><img src="image_10.png" /></figure>

The domain wall width increases on the picosecond timescales

## Conclusion

We attribute this increase in domain wall width to a modification of the magnetic anisotropy since $d \propto \sqrt{\frac{A}{K_u}}$, where A is the exchange stiffness (which we suppose mostly constant) and $K_u$ is the magnetic anisotropy.

## References

1. B. Vodungbo et al., Nat. Commun. 3, 999 (2012).

2. O. Hellwig et al., Phys. B: Condens. Matter 336, 136 (2003).

3. M. Hennes et al., Phys. Rev. B 102, 174437 (2020).