Straight motion of half-integer topological defects in thin Fe-N magnetic films with stripe domains

Abstract

In thin magnetic films with perpendicular magnetic anisotropy, a periodic “up-down” stripe-domain structure can be originated at remanence, on a mesoscopic scale (~100 nm) comparable with film thickness, by the competition between short-range exchange coupling and long-range dipolar interaction. However, translational order is perturbed because magnetic edge dislocations are spontaneously nucleated. Such topological defects play an important role in magnetic films since they promote the in-plane magnetization reversal of stripes and, in superconductor/ferromagnet hybrids, the creation of superconducting vortex clusters. Combining magnetic force microscopy experiments and micromagnetic simulations, we investigated the motion of two classes of magnetic edge dislocations, randomly distributed in an -implanted Fe film. They were found to move in opposite directions along straight trajectories parallel to the stripes axis, when driven by a moderate dc magnetic field. Using the approximate Thiele equation, analytical expressions for the forces acting on such magnetic defects and a microscopic explanation for the direction of their motion could be obtained. Straight trajectories are related to the presence of a periodic stripe domain pattern, which imposes the gyrotropic force to vanish even if a nonzero, half-integer topological charge is carried by the defects in some layers across the film thickness.

Stripe domains reorientation in ferromagnetic films with perpendicular magnetic anisotropy

“…We obtained K PMA in the range from 5 to 7×10 6 erg cm −3 (see figure 7(c) later on), consistent with the reported values for the magnetocrystalline anisotropy of α′-Fe 8 N 1−x [85,86], and in agreement with K PMA values measured by ferromagnetic resonance [87]. We note that, assuming M s =1700 emu cm −3 [31], the quality factor Q of the Fe-N samples investigated in this work is between 0.275 and 0.385, depending on the preparation conditions, while the critical thickness above which the stripe domains appear is about 40 nm.…”

“…Weak stripe domains were first predicted theoretically [32,33] and later discovered experimentally in NiFe films [19,34]. In the following years, the phenomenon has been found and deepened in different kinds of thin films with moderate PMA, such as FeGa [35][36][37][38], FeN [31,39,40], FeSiB [41,42], CoFeB [43], FeTaN [44], GdFe [45], NdCo [46], FeCoZr [23], La x Sr 1−x MnO 3 [47] and multilayers with moderate perpendicular anisotropy [48][49][50]. Very recently, it has been shown [51] that the formation of stripe domains can be induced in a Py film, even far below the critical thickness, by coupling the Py film to a NdCo one, characterized by a moderate PMA.…”

“…Typically, within such approaches the magnetostatic interaction associated with the stripe pattern is properly evaluated by taking into account a realistic, although simplified, magnetization profile across the stripes, such as in [18][19][20][21][22][23][24] (1D models), and/or across the film thickness, such as in [25,26] (2D models). Alternatively, a numerical micromagnetic calculation can be performed, but the limitation of such an approach is related to the finite size of the film plane [27][28][29][30][31].…”

Probing the pinning strength of magnetic vortex cores with sub-nanometer resolution

“…Here, we employ spin polarized scanning tunneling microscopy (STM) to study pinning of the curled magnetization of a magnetic vortex core 22,23 . We apply well defined lateral forces by in-plane magnetic fields B ∥ 24 and independently tune the size of the vortex core by an out-of-plane field B ⊥ . The latter enables control on the non-collinearity of the core magnetization and, hence, on the strength of exchange energy density u exch in the core.…”

Topological Charge of Soft X-ray Vortex Beam Determined by Inline Holography

“…4 (a)), have been commonly observed in several magnetic textures, including ferromagnetic stripe, helical, and skyrmion domain structures. Previous studies have reported the dynamics of topological defects in these magnetic textures under thermal fluctuation or a magnetic field 17,[27][28][29] .…”