Domain wall pinning on strain relaxation defects in FePt(001)/Pt thin films

Abstract

Thin FePt (001) films, grown by molecular-beam epitaxy on Pt(001), exhibit a very large perpendicular magnetic anisotropy (Ku=5×106 J m−3) and a 100% magnetic remanence in perpendicular field. The lattice misfit between FePt and Pt (1.5%) relaxes through the pileup of a/6 〈112〉 partial dislocations along {111} planes, leading to the formation of microtwins. Atomic force microscopy images demonstrate that this process induces a spontaneous rectangular nanostructuration of the sample, while magnetic force microscopy shows that the microtwins act as pinning sites for the magnetic walls. This leads to square magnetic domains and explains the large coercivity associated with the domain wall propagation.

Magnetic domain wall pinning and coercivity in FePt/MgO and FePt/Pt thin films

“…This is due to the dipolar field that favors a vertical alignment of the DW and thus the depinning. However, it has been shown [18] that the average number of atomic layers in the microtwin increases quasi-linearly with the alloy thickness, up to approximately 25 atomic planes in 40 nm FePt layers [15]. The variation of the depinning field as a function of the width of the microtwin is shown in Fig.…”

“…Thus the presence of antiphase boundaries cannot account for the decrease in the coercive field as the thickness increases. Interface dislocations are therefore probably Whereas it is difficult to address the source of coercivity in FePt/MgO samples, it is well established in FePt/Pt samples [15]: it is linked to the pinning of DW on structural defects named microtwins. Microtwins are extended defects generated by the relaxation of the tensile epitaxial strain.…”

“…1c and d). The coercive field shall not be associated with a difficult nucleation followed by an easy propagation of the DW: the sample is magnetically remanent in partially reversed states, which implies that the strong coercivity is due to DW pinning on defects [15,16].…”

Self-assembling of alloy nanostructures on van der Waals surfaces

“…Submonolayers and thicker deposits (30 Å thick) were obtained for substrate temperatures between 20 and 700 C: The co-deposition of Fe and Pt atoms on WSe 2 was done at the Laboratory of Nanostructures and Magnetism at the CEA-Grenoble [7]. For all deposits, the epitaxial growth was checked by in situ reflection high-energy diffraction(RHEED).…”

Interparticle interactions in annealed FePt nanoparticle assemblies

“…The initial magnetization curve for the sample annealed at 700 C suggests that the magnetization reversal is governed by domain nucleation process [12]. Interestingly, exchange coupled thin films prepared by sputtering often show pinning reversal mechanisms [13]. Fig.…”