Ferromagnetic thin films with moderate perpendicular magnetic anisotropy (PMA) are known to support weak stripe domains provided film thickness exceeds a critical value. In this work, we performed both an experimental and theoretical investigation of a peculiar phenomenon shown by weak stripe domains: namely, the stripe domains reorientation when a dc magnetic field is applied in the film plane along the direction perpendicular to the stripes axis. We focus on bct α′-Fe 8 N 1−x thin films obtained by + N 2 implantation of α-Fe films epitaxially grown on ZnSe/GaAs(001). By using different ion implantation and heat treatment conditions, we show that it is possible to tune the PMA values. Magnetic force microscopy and vibrating sample magnetometer measurements prove the existence of weak stripe domains at remanence, and of a threshold field for the reorientation of the stripes axis in a transversal field. Using a one-dimensional model of the magnetic stripe domains, where the essential parameter is the maximum canting angle of the stripe magnetization out of the film plane, the various contributions to the magnetic energy can be separately calculated. A linear increase of the reorientation threshold field on the PMA is obtained, in qualitative agreement with experimental data in our Fe-N films, as well as in other thin films with weak stripe domains. Finally, we find that also the rotatable anisotropy field linearly increases as a function of the PMA magnitude.

The magnetic properties of an iron nitride thin film obtained by ion implantation have been\ud investigated. N2+ ions were implanted in a pristine iron layer epitaxially grown on ZnSe/GaAs\ud (001). X-ray diffraction measurements revealed the formation of body-centered tetragonal\ud N-martensite whose c-axis is perpendicular to the thin film plane and c-parameter is close to that\ud of alpha' Fe8N. Magnetic measurements disclosed a weak perpendicular magnetic anisotropy (PMA)\ud whose energy density KPMA was assessed to about 105 J/m3. A sharp decline of the in-plane\ud magnetocrystalline anisotropy (MCA) was also observed, in comparison with the body-centered\ud cubic iron. The origin of the PMA is attributed to the MCA of N-martensite and/or stress-induced\ud anisotropy. As a result of the PMA, weak magnetic stripe domains with a period of about 130nm\ud aligned along the last saturating magnetic field direction were observed at remanence by magnetic force microscopy. The application of an increasing in-plane magnetic field transverse to the stripes\ud Htrans highlighted a threshold value above which these magnetic domains irreversibly\ud rotated. Interestingly, below this threshold, the stripes do not rotate, leading to a zero\ud remanent magnetization along the direction of the applied field. The interest of this system for\ud magnetization dynamics is discussed

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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.