We have studied the effect of He+ irradiation on the dynamics of chiral domain walls in Pt/Co/AlOx trilayers in the creep regime. Irradiation leads to a strong decrease in the depinning field and a non-monotonous change of the effective pinning barriers. The variations of domain wall dynamics result essentially from the strong decrease in the effective anisotropy constant, which increases the domain wall width. The latter is found to present a perfect scaling with the length-scale of the interaction between domain wall and disorder, ξ. On the other hand, the strength of the domain wall–disorder interaction, fpin, is weakly impacted by the irradiation, suggesting that the length-scales of the disorder fluctuation remain smaller than the domain wall width.

One of the most critical technological issues that hinders the application of magnetic textures, such as domain walls (DWs) and skyrmions, to high performance spintronic devices is their interaction with defects. Material inhomogeneities act as pinning sites for magnetic textures, limiting their velocities for small driving torques (i.e., for fields or currents below the depinning threshold, in the so-called creep regime) and preventing reproducible displacement events. To control the motion of magnetic textures, a better understanding of their interaction with the pinning disorder would be particularly welcome.

In this frame, ion irradiation is an interesting tool since it allows both tuning the magnetic properties of ultrathin films1–81. C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, and H. Launois, “ Planar patterned magnetic media obtained by ion irradiation,” Science 280, 1919–1922 (1998). https://doi.org/10.1126/science.280.5371.19192. T. Devolder, “ Light ion irradiation of Co/Pt systems: Structural origin of the decrease in magnetic anisotropy,” Phys. Rev. B 62, 5794–5802 (2000). https://doi.org/10.1103/PhysRevB.62.57943. T. Devolder, S. Pizzini, J. Vogel, H. Bernas, C. Chappert, V. Mathet, and M. Borowski, “ X-ray absorption analysis of sputter-grown Co/Pt stackings before and after helium irradiation,” Eur. Phys. J. B 22, 193 (2001). https://doi.org/10.1007/s1005101701274. J. Fassbender, D. Ravelosona, and Y. Samson, “ Tailoring magnetism by light-ion irradiation,” J. Phys. D: Appl. Phys. 37, R179 (2004). https://doi.org/10.1088/0022-3727/37/16/R015. A. L. Balk, K.-W. Kim, D. T. Pierce, M. D. Stiles, J. Unguris, and S. M. Stavis, “ Simultaneous control of the Dzyaloshinskii–Moriya interaction and magnetic anisotropy in nanomagnetic trilayers,” Phys. Rev. Lett. 119, 077205 (2017). https://doi.org/10.1103/PhysRevLett.119.0772056. A. Sud, S. Tacchi, D. Sagkovits, C. Barton, M. Sall, L. H. Diez, E. Stylianidis, N. Smith, L. Wright, S. Zhang, X. Hang, D. Ravelosona, G. Carlotti, H. Kurebayashi, O. Kazakova, and M. Cubukcu, “ Tailoring interfacial effect in multilayers with Dzyaloshinskii–Moriya interaction by helium ion irradiation,” Sci. Rep. 11, 023626 (2021). https://doi.org/10.1038/s41598-021-02902-y7. R. Juge, K. Bairagi, K. G. Rana, J. Vogel, M. Sall, D. Mailly, V. T. Pham, Q. Zhang, N. Sisodia, M. Foerster, L. Aballe, M. Belmeguenai, Y. Roussigné, S. Auffret, L. D. Buda-Prejbeanu, G. Gaudin, D. Ravelosona, and O. Boulle, “ Helium ions put magnetic skyrmions on the track,” Nano Lett. 21, 2989–2996 (2021). https://doi.org/10.1021/acs.nanolett.1c001368. M. C. H. de Jong, M. J. Meijer, J. Lucassen, J. van Liempt, H. J. M. Swagten, B. Koopmans, and R. Lavrijsen, “ Local control of magnetic interface effects in chiral Ir|Co|Pt multilayers using Ga+ ion irradiation,” Phys. Rev. B 105, 064429 (2022). https://doi.org/10.1103/PhysRevB.105.064429 and modifying DW dynamics.9,109. L. H. Diez, F. García-Sánchez, J.-P. Adam, T. Devolder, S. Eimer, M. S. E. Hadri, A. Lamperti, R. Mantovan, B. Ocker, and D. Ravelosona, “ Controlling magnetic domain wall motion in the creep regime in He+-irradiated CoFeB/MgO films with perpendicular anisotropy,” Appl. Phys. Lett. 107, 032401 (2015). https://doi.org/10.1063/1.492720410. J. W. van der Jagt, V. Jeudy, A. Thiaville, M. Sall, N. Vernier, L. Herrera Diez, M. Belmeguenai, Y. Roussigné, S. M. Chérif, M. Fattouhi, L. Lopez-Diaz, A. Lamperti, R. Juge, and D. Ravelosona, “ Revealing nanoscale disorder in W/Co-Fe-B/MgO ultrathin films using domain-wall motion,” Phys. Rev. Appl. 18, 054072 (2022). https://doi.org/10.1103/PhysRevApplied.18.054072 Early studies on Pt/Co/Pt multilayers showed that He+ ions with energy in the 30 keV range provoke short-range (0.2–0.5 nm) atomic displacements through low energy collisions.1,2,111. C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, and H. Launois, “ Planar patterned magnetic media obtained by ion irradiation,” Science 280, 1919–1922 (1998). https://doi.org/10.1126/science.280.5371.19192. T. Devolder, “ Light ion irradiation of Co/Pt systems: Structural origin of the decrease in magnetic anisotropy,” Phys. Rev. B 62, 5794–5802 (2000). https://doi.org/10.1103/PhysRevB.62.579411. J. Ferré, C. Chappert, H. Bernas, J.-P. Jamet, P. Meyer, O. Kaitasov, S. Lemerle, V. Mathet, F. Rousseaux, and H. Launois, “ Irradiation induced effects on magnetic properties of Pt/Co/Pt ultrathin films,” J. Magn. Magn. Mater. 198–199, 191–193 (1999). https://doi.org/10.1016/S0304-8853(98)01084-1 The resulting Co/Pt intermixing gradually evolves with increasing fluences, therefore tuning the interfacial perpendicular magnetic anisotropy (PMA).1212. D. Weller, J. Stöhr, R. Nakajima, A. Carl, M. G. Samant, C. Chappert, R. Mégy, P. Beauvillain, P. Veillet, and G. A. Held, “ Microscopic origin of magnetic anisotropy in Au/Co/Au probed with x-ray magnetic circular dichroism,” Phys. Rev. Lett. 75, 3752–3755 (1995). https://doi.org/10.1103/PhysRevLett.75.3752 Although ion irradiation has been observed to change the DW dynamics of several ultrathin films in the creep regime,9,109. L. H. Diez, F. García-Sánchez, J.-P. Adam, T. Devolder, S. Eimer, M. S. E. Hadri, A. Lamperti, R. Mantovan, B. Ocker, and D. Ravelosona, “ Controlling magnetic domain wall motion in the creep regime in He+-irradiated CoFeB/MgO films with perpendicular anisotropy,” Appl. Phys. Lett. 107, 032401 (2015). https://doi.org/10.1063/1.492720410. J. W. van der Jagt, V. Jeudy, A. Thiaville, M. Sall, N. Vernier, L. Herrera Diez, M. Belmeguenai, Y. Roussigné, S. M. Chérif, M. Fattouhi, L. Lopez-Diaz, A. Lamperti, R. Juge, and D. Ravelosona, “ Revealing nanoscale disorder in W/Co-Fe-B/MgO ultrathin films using domain-wall motion,” Phys. Rev. Appl. 18, 054072 (2022). https://doi.org/10.1103/PhysRevApplied.18.054072 the microscopic origin of these effects remains an open issue, as ion irradiation may modify both the pinning disorder and the DW magnetic texture (via the film PMA) and, thus, the DW-disorder interaction.Recent developments in the understanding of pinning dependent dynamics of DWs driven by a magnetic field13,1413. V. Jeudy, A. Mougin, S. Bustingorry, W. Savero Torres, J. Gorchon, A. B. Kolton, A. Lemaître, and J.-P. Jamet, “ Universal pinning energy barrier for driven domain walls in thin ferromagnetic films,” Phys. Rev. Lett. 117, 057201 (2016). https://doi.org/10.1103/PhysRevLett.117.05720114. R. D. Pardo, W. Savero Torres, A. B. Kolton, S. Bustingorry, and V. Jeudy, “ Universal depinning transition of domain walls in ultrathin ferromagnets,” Phys. Rev. B 95, 184434 (2017). https://doi.org/10.1103/PhysRevB.95.184434 and an electrical current (via the spin transfer torque)1515. R. Díaz Pardo, N. Moisan, L. J. Albornoz, A. Lemaître, J. Curiale, and V. Jeudy, “ Common universal behavior of magnetic domain walls driven by spin-polarized electrical current and magnetic field,” Phys. Rev. B 100, 184420 (2019). https://doi.org/10.1103/PhysRevB.100.184420 provide quantitative assessments on DW–disorder interactions. The pinning dependent dynamics of DWs results from the interplay among DW elasticity, weak pinning, thermal activation, and a driving force.1616. S. Lemerle, J. Ferré, C. Chappert, V. Mathet, T. Giamarchi, and P. Le Doussal, “ Domain wall creep in an Ising ultrathin magnetic film,” Phys. Rev. Lett. 80, 849 (1998). https://doi.org/10.1103/PhysRevLett.80.849 The thermally activated creep regime1313. V. Jeudy, A. Mougin, S. Bustingorry, W. Savero Torres, J. Gorchon, A. B. Kolton, A. Lemaître, and J.-P. Jamet, “ Universal pinning energy barrier for driven domain walls in thin ferromagnetic films,” Phys. Rev. Lett. 117, 057201 (2016). https://doi.org/10.1103/PhysRevLett.117.057201 and depinning1414. R. D. Pardo, W. Savero Torres, A. B. Kolton, S. Bustingorry, and V. Jeudy, “ Universal depinning transition of domain walls in ultrathin ferromagnets,” Phys. Rev. B 95, 184434 (2017). https://doi.org/10.1103/PhysRevB.95.184434 regime observed below and just above the depinning threshold present well studied universal behaviors, which are in agreement with predictions for the quenched Edwards–Wilkinson universality class.1717. L. J. Albornoz, P. C. Guruciaga, V. Jeudy, J. Curiale, and S. Bustingorry, “ Domain-wall roughness in GdFeCo thin films: Crossover length scales and roughness exponents,” Phys. Rev. B 104, 024203 (2021). https://doi.org/10.1103/PhysRevB.104.024203 Combining a self-consistent description of the creep and depinning regimes and a scaling model of DW depinning, the analysis of domain wall dynamics allows extracting the parameters characterizing the interaction between domain walls and weak pinning disorder.1818. P. Géhanne, S. Rohart, A. Thiaville, and V. Jeudy, “ Strength and length scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films,” Phys. Rev. Res. 2, 043134 (2020). https://doi.org/10.1103/PhysRevResearch.2.043134

In this work, we analyze the evolution with He+ fluence of micromagnetic parameters and DW dynamics in a series of Pt/Co/AlOx ultrathin films presenting the same initial disorder. We evidence a perfect scaling between DW width parameter and DW-disorder interaction length scale, directly reflecting the strong decrease in the PMA. On the other hand, the strong correlation between the pinning strength and DW energy is compatible with negligible effect of He+ irradiation on the pinning disorder.

Ta(4)/Pt(4)/Co(1.1)/Al(2) magnetic stacks (thicknesses in nm) were deposited by magnetron sputtering on Si/SiO2 wafers; the Al layer was consequently oxidized with an oxygen plasma. The film was diced into small samples: one of them was kept in the pristine state, while the others were irradiated at room temperature with 15 kV He* ions, with fluence ranging from 4 × 1014 to 1.5 × 1015 He+/cm2. The measured magnetic parameters are presented in Table I. The spontaneous magnetization Ms and the anisotropy field μ0Hk were measured by superconducting quantum interference vibrating sample magnetometry. All the samples present an out-of-plane easy magnetization axis. The in-plane saturation field strongly decreases as the He+ fluence increases, while the spontaneous magnetization is, within the uncertainty of the measurement, unchanged.

TABLE I. Micromagnetic parameters measured for the Pt/Co/AlOx film in the pristine state and after irradiation with He+ ions. For each sample, the table indicates the He+ irradiation fluence, the spontaneous magnetization Ms, the anisotropy field μ0HK, the anisotropy constant Keff=μ0HKMs/2, the DW width parameter Δ=A/Keff, the DW saturation velocity vsat obtained for high magnetic fields, the interfacial DMI constant D obtained using D=2Msvsat/(γπ), and the DW energy σ=4AKeff−πD using A = 16 pJ/m.

SampleHe+fluence (ions/cm2)Ms (MA/m)μ0HK (T)Keff (105 J/m3)vsat (m/s)Δ (nm)D (mJ/m2)σ (mJ/m2)Pristine01.13 ± 0.03785 ± 404.44 ± 0.25260 ± 156.0 ± 0.21.06 ± 0.087.32 ± 0.6F14.0 × 10141.13 ± 0.03727 ± 404.11 ± 0.24270 ± 156.3 ± 0.21.10 ± 0.086.78 ± 0.6F21.0 × 10151.16 ± 0.03446 ± 252.59 ± 0.15270 ± 157.9 ± 0.21.13 ± 0.084.58 ± 0.6F31.5 × 10151.17 ± 0.03305 ± 161.78 ± 0.10270 ± 159.5 ± 0.21.14 ± 0.083.17 ± 0.6The field-driven domain wall dynamics was measured using polar magneto-optical Kerr microscopy. For the lowest DW velocities, out-of-plane magnetic field pulses were applied using an electromagnet (maximum pulse amplitude μ0Hz = 25 mT, minimum duration 20 ms). For the higher velocities, pulses of maximum amplitude μ0Hz = 200 mT and minimum duration 30 ns were delivered by a 200 μm-diameter microcoil associated with a fast pulse current generator.1919. T. H. Pham, J. Vogel, J. Sampaio, M. Vanatka, J.-C. Rojas-Sanchez, M. Bonfim, D. S. Chaves, F. Choueikani, P. Ohresser, E. Otero, A. Thiaville, and S. Pizzini, “ Very large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers with Dzyaloshinskii–Moriya interaction,” EPL 113, 67001 (2016). https://doi.org/10.1209/0295-5075/113/67001 The film magnetization was first saturated in the out-of-plane direction. An opposite magnetic field pulse was then applied to nucleate a reverse domain. The velocity of DWs was deduced from their displacement observed after the magnetic field pulse and corresponds to the ratio between the displacement and the pulse duration. The presence of left-handed homochiral Néel walls2020. A. Thiaville, S. Rohart, E. Jué, V. Cros, and A. Fert, “ Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films,” EPL 100, 57002 (2012). https://doi.org/10.1209/0295-5075/100/57002 associated with the presence of Dzyaloshinskii–Moriya interaction (DMI)21,2221. I. E. Dzyaloshinskii, “ Thermodynamic theory of ‘weak’ ferromagnetism in antiferromagnetic substances,” Sov. Phys. JETP 5, 1259 (1957).22. T. Moriya, “ Anisotropic superexchange interaction and weak ferromagnetism,” Phys. Rev. 120, 91 (1960). https://doi.org/10.1103/PhysRev.120.91 was confirmed by the non-isotropic displacement of the DWs in the presence of a static in-plane magnetic field μ0Hx (not shown). The strength of the DMI interaction was obtained from the DW saturation velocity at large Bz fields vsat=γπD/(2Ms), using the experimental values of Ms.19,2319. T. H. Pham, J. Vogel, J. Sampaio, M. Vanatka, J.-C. Rojas-Sanchez, M. Bonfim, D. S. Chaves, F. Choueikani, P. Ohresser, E. Otero, A. Thiaville, and S. Pizzini, “ Very large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers with Dzyaloshinskii–Moriya interaction,” EPL 113, 67001 (2016). https://doi.org/10.1209/0295-5075/113/6700123. V. Krizakova, J. Peña Garcia, J. Vogel, D. de Souza Chaves, S. Pizzini, and A. Thiaville, “ Study of the velocity plateau of Dzyaloshinskii domain walls,” Phys. Rev. B 100, 214404 (2019). https://doi.org/10.1103/PhysRevB.100.214404The domain wall velocities driven by out-of-plane magnetic fields up to 200 mT are reported in Fig. 1 for the samples in the pristine state and after irradiation. As it can be observed, the strongest trend is a shift of the curves toward low field values with increasing irradiation fluence. More quantitative insight into the DW dynamics can be deduced from the self-consistent description of the creep and depinning regimes proposed in Refs. 1313. V. Jeudy, A. Mougin, S. Bustingorry, W. Savero Torres, J. Gorchon, A. B. Kolton, A. Lemaître, and J.-P. Jamet, “ Universal pinning energy barrier for driven domain walls in thin ferromagnetic films,” Phys. Rev. Lett. 117, 057201 (2016). https://doi.org/10.1103/PhysRevLett.117.057201, 1414. R. D. Pardo, W. Savero Torres, A. B. Kolton, S. Bustingorry, and V. Jeudy, “ Universal depinning transition of domain walls in ultrathin ferromagnets,” Phys. Rev. B 95, 184434 (2017). https://doi.org/10.1103/PhysRevB.95.184434, and 2424. V. Jeudy, R. Díaz Pardo, W. Savero Torres, S. Bustingorry, and A. B. Kolton, “ Pinning of domain walls in thin ferromagnetic films,” Phys. Rev. B 98, 054406 (2018). https://doi.org/10.1103/PhysRevB.98.054406 v(Hz)={v(Hd) exp [−TdT((HdHz)μ−1)]creep:Hz<Hd,v(Hd)x0(TdT)ψ(Hz−HdHd)βdepinning:Hz≳Hd,(1)where μ=1/4, β=0.25, and ψ=0.15 are universal critical exponents and x0=0.65 is a universal constant.14,2514. R. D. Pardo, W. Savero Torres, A. B. Kolton, S. Bustingorry, and V. Jeudy, “ Universal depinning transition of domain walls in ultrathin ferromagnets,” Phys. Rev. B 95, 184434 (2017). https://doi.org/10.1103/PhysRevB.95.18443425. S. Bustingorry, A. B. Kolton, and T. Giamarchi, “ Thermal rounding exponent of the depinning transition of an elastic string in a random medium,” Phys. Rev. E 85, 021144 (2012). https://doi.org/10.1103/PhysRevE.85.021144 In Eqs. (1), the three adjustable parameters depend on the film magnetic and pinning properties: the depinning temperature Td characterizing the height of the effective pinning barrier, the depinning field Hd, and the velocity v(Hd), corresponding to the coordinates of the crossover between creep and depinning. Good agreement between the experimental curves and the fit using Eqs. (1) [Figs. 1(a) and 1(b)] indicates the crossover between the creep and depinning regimes. The evolution of the depinning parameters with the irradiation fluence is reported in Fig. 2. The irradiation has no effect on the depinning velocity v(Hd), which remains rather constant. Td varies slightly with a non-monotonous trend. In contrast, Hd decreases by a factor ≈2 with the irradiation fluence (from around 80 mT for the pristine sample down to 40 mT for 1.5 × 1015 He+/cm2). As a consequence, in the irradiated samples, the DWs can reach the largest velocities for lower applied magnetic fields. Note that our results are not compatible with the assumption σ∼TdHd1/4 proposed by Je et al.2626. S.-G. Je, D.-H. Kim, S.-C. Yoo, B.-C. Min, K.-J. Lee, and S.-B. Choe, Phys. Rev. B 88, 214401 (2013). https://doi.org/10.1103/PhysRevB.88.214401 The slope of the creep law in Fig. 1(b) (∝TdHd1/4) does not vary with the He+ fluence. The DW energy is defined2020. A. Thiaville, S. Rohart, E. Jué, V. Cros, and A. Fert, “ Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films,” EPL 100, 57002 (2012). https://doi.org/10.1209/0295-5075/100/57002 by σ=4AKeff−πD, where A is the exchange stiffness, Keff is the effective anisotropy constant, and D is the DMI constant. Using the measured Keff and D and setting A = 16 pJ/m (the value we estimated for similar Pt/Co/AlOx trilayers in Ref. 1919. T. H. Pham, J. Vogel, J. Sampaio, M. Vanatka, J.-C. Rojas-Sanchez, M. Bonfim, D. S. Chaves, F. Choueikani, P. Ohresser, E. Otero, A. Thiaville, and S. Pizzini, “ Very large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers with Dzyaloshinskii–Moriya interaction,” EPL 113, 67001 (2016). https://doi.org/10.1209/0295-5075/113/67001), we find, on the other hand, that the DW energy varies by more than a factor 2 (see Table I).In order to discuss the evolution of the interaction between DWs and disorder as a function of the irradiation fluence, we use the scaling model developed in Ref. 1818. P. Géhanne, S. Rohart, A. Thiaville, and V. Jeudy, “ Strength and length scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films,” Phys. Rev. Res. 2, 043134 (2020). https://doi.org/10.1103/PhysRevResearch.2.043134. This model allows us to link the characteristic length scale ξ and the force fpin of the interaction between DW and disorder to the measured depinning field Hd, the temperature Td, and the micromagnetic parameters, i.e., the DW energy σ and the spontaneous magnetization Ms, ξ∼[(kBTd)2/(2μ0HdMsσt2)]1/3,(2) fpin∼bξ2μ0HdMstkBTd.(3)In the above equations, kB is the Boltzmann constant, t is the magnetic film thickness, and b is the characteristic distance between pinning sites. Figure 3(a) compares the evolution of ξ and of the DW parameter Δ as a function of the irradiation fluence. As it can be observed, rescaling ξ with a single adjustable parameter (Δ≈2.9ξ) leads to a superposition with the values of Δ. This almost perfect scaling strongly suggests that the characteristic distance between pinning sites b is smaller than Δ, so that the latter fixes the length-scale of the DW-disorder interaction.18,2718. P. Géhanne, S. Rohart, A. Thiaville, and V. Jeudy, “ Strength and length scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films,” Phys. Rev. Res. 2, 043134 (2020). https://doi.org/10.1103/PhysRevResearch.2.04313427. T. Nattermann, “ Scaling approach to pinning: Charge density waves and giant flux creep in superconductors,” Phys. Rev. Lett. 64, 2454 (1990). https://doi.org/10.1103/PhysRevLett.64.2454 As a consequence, the predicted short-range atomic displacements produced by He+ ions irradiation2,32. T. Devolder, “ Light ion irradiation of Co/Pt systems: Structural origin of the decrease in magnetic anisotropy,” Phys. Rev. B 62, 5794–5802 (2000). https://doi.org/10.1103/PhysRevB.62.57943. T. Devolder, S. Pizzini, J. Vogel, H. Bernas, C. Chappert, V. Mathet, and M. Borowski, “ X-ray absorption analysis of sputter-grown Co/Pt stackings before and after helium irradiation,” Eur. Phys. J. B 22, 193 (2001). https://doi.org/10.1007/s100510170127 have no impact on the characteristic length of DW-pinning interaction ξ. The observed variation of ξ only reflects the strong decrease in the effective anisotropy constant with the increasing irradiation fluence.Figure 3(b) compares the evolution of the pinning force fpin and the DW energy per unit length σt. In this case, we assumed a common distance between pinning sites b = 1 nm, and we used a single scaling parameter (=9) to superimpose the data points corresponding to the pristine film. fpin and σt are observed to follow a similar decreasing trend with irradiation fluence. Note that a similar phenomenon was already observed for Pt/Co/Pt, Pt/Co/Au, and Au/Co/Pt trilayers in Ref. 1818. P. Géhanne, S. Rohart, A. Thiaville, and V. Jeudy, “ Strength and length scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films,” Phys. Rev. Res. 2, 043134 (2020). https://doi.org/10.1103/PhysRevResearch.2.043134. In that work, the samples had a fixed disorder, and the DW width and energy were controlled by an in-plane magnetic field.1818. P. Géhanne, S. Rohart, A. Thiaville, and V. Jeudy, “ Strength and length scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films,” Phys. Rev. Res. 2, 043134 (2020). https://doi.org/10.1103/PhysRevResearch.2.043134 In the present case, as the samples share initially the same pinning disorder, the observed close trend of fpin and σt suggests a weak change of the disorder by irradiation. Assuming a perfect scaling between fpin and σt [i.e., adjusting the value of b to perfectly superimpose the data points in Fig. 3(b)] leads a rough estimate of the maximum variation of b ≈−15%. These insights suggest that the He+ irradiation has little impact on the pinning disorder, and the variation of the strength DW-disorder interaction fpin essentially reflects the decrease in the effective anisotropy constant with irradiation fluence.

In conclusion, light He+ irradiation in Pt/Co/AlOx ultrathin films causes a strong reduction in the depinning field, leading to an increase the DW mobility at low magnetic fields. Through a self-consistent description of the creep and pinning dynamics completed by a scaling model of DW depinning (relating DW pinning properties to depinning and micromagnetic parameters), we reveal an excellent scaling between the variations of the DW-disorder interaction length scale ξ and the DW width parameter. This scaling strongly suggests that the modifications of the DW pinning are essentially dominated by the variations of the DW magnetic texture (via the variation of the film anisotropy) while the short range atomic displacements produced by the irradiation have a weak impact on the pinning disorder.

We acknowledge the support of the Agence Nationale de la Recherche (Project No. ANR-17-CE24-0025) (TOPSKY). The authors acknowledge funding from the European Union's Horizon 2020 Research and Innovation Program “Magnetism and the effect of Electric Field” (MagnEFi) under Marie Sklodowska-Curie Grant Agreement Nos. 754303 and 860060. J.P.G. also thanks the Laboratoire d' Excellence LANEF in Grenoble (No. ANR-10-LABX-0051) for its support. B. Fernandez, T. Crozes, Ph. David, E. Mossang, and E. Wagner are acknowledged for their technical help.

Conflict of Interest

The authors have no conflicts to disclose.

Author Contributions

Cristina Balan: Conceptualization (equal); Investigation (equal) Johannes W. van der Jagt: Conceptualization (equal); Investigation (equal); Methodology (equal). Jose Peña Garcia: Software (equal); Visualization (equal). Jan Vogel: Investigation (equal). Laurent Ranno: Conceptualization (equal); Supervision (equal). Marlio Bonfim: Methodology (equal). Dafiné Ravelosona: Conceptualization (equal); Funding acquisition (equal); Methodology (equal); Supervision (equal). Stefania Pizzini: Conceptualization (lead); Funding acquisition (equal); Investigation (equal); Methodology (equal); Supervision (equal); Visualization (equal); Writing – review and editing (lead). Vincent Jeudy: Conceptualization (equal); Software (lead); Methodology (equal); Visualization (equal); Writing – review and editing (equal).

The data that support the findings of this study are available within the article.

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