Enhanced film thickness for Néel wall in soft magnetic film by introducing strong magnetocrystalline anisotropy

Abstract

This study investigated the magnetic domain walls in a single-layer soft magnetic film with strong magnetocrystalline anisotropy energy. The soft magnetic film is composed of a highly c-axis-oriented hcp-Co81Ir19 alloy with strong negative magnetocrystalline anisotropy. The domain structure of the soft Co81Ir19 films with thickness ranging from 50–230 nm in a demagnetization state was observed through magnetic force microscopy and Lorentz transmission electron microscopy. Results reveal that the critical transition thickness at which the domain wall changes from Néel type to Bloch type is about 138 nm, which is much larger than the critical value of traditional Fe- and Co-based soft magnetic films with negligible magnetocrystalline anisotropy. Theoretical calculation was also performed and the calculated result agrees well with experimental data.

Surface Roughness Influence on Néel-, Crosstie, and Bloch-Type Charged Zigzag Magnetic Domain Walls in Nanostructured Fe Films

“…Magnetic walls are often used as the key parameters in non-volatile memory devices [ 17 ]. Comprehensive knowledge of the magnetic domain structures is also necessary from an applied point of view [ 18 ], as domain structure investigations provide information about the energetic balance among the interactions that stabilize the ferromagnetic structure, such as magnetostatic, exchange, and anisotropy energy. So, the study of magnetic domain structures is important, and they are continuously the object of analysis and research [ 19 , 20 , 21 , 22 , 23 ].…”

Playing with universality classes of Barkhausen avalanches

“…In soft ferromagnetic films with in-plane magnetic domains, despite the diversity of DW (Bloch walls, symmetric and asymmetric Néel walls, and the conspicuous cross-tie wall, this latter a complex pattern of Néel wall), the basic types of DW are simply Bloch and Néel walls. The type of domain wall will depend on the domain wall energy 61 , 62 , which in turn for both wall types is dependent on the thickness, domain-wall thickness, effective magnetic anisotropy, saturation magnetization and exchange stiffness constant, or, in other words, is a result of the sum of the magnetostatic, exchange and anisotropy energy contributions 14 , 15 , 61 , 62 . Generally, the domain wall assumes the form of Bloch wall (in which an out-of-plane stray field exists in the domain wall due to the rotation of magnetic moments occurs in a perpendicular direction from the adjacent domains) when the film is thicker; and it will become Néel wall (in which the magnetic moments inside the wall strictly lie in the film plane, thus reducing the magnetostatic contribution to the wall energy) when the film thickness is below a critical value 14 , 15 , 61 – 63 .…”

“…Specifically, magnetic domains and domain walls are influenced by the film thickness due to the increasing importance of stray fields along the direction normal to the plane 12 . Between 100 and 50 nm, the thickness becomes of the same order of magnitude of the DW width and the stray fields constitute an appreciable source of magnetostatic energy, having straight impact on the inner structure of the DW 14 , 15 , 61 , 62 and, therefore, on the DW motion. Thereby, from the phenomenological point of view, the dimensional crossover may be seen as a consequence of this change in the type of DW, the Bloch-Néel transition.…”

“…The type of domain wall will depend on the domain wall energy 61,62 , which in turn for both wall types is dependent on the thickness, domain-wall thickness, effective magnetic anisotropy, saturation magnetization and exchange stiffness constant, or, in other words, is a result of the sum of the magnetostatic, exchange and anisotropy energy contributions 14,15,61,62 . Generally, the domain wall assumes the form of Bloch wall (in which an out-of-plane stray field exists in the domain wall due to the rotation of magnetic moments occurs in a perpendicular direction from the adjacent domains) when the film is thicker; and it will become Néel wall (in which the magnetic moments inside the wall strictly lie in the film plane, thus reducing the magnetostatic contribution to the wall energy) when the film thickness is below a critical value 14,15,[61][62][63] . Actually, classical books 14,15 and reports addressing theoretically and experimentally the stability of DW in films [61][62][63][64][65][66][67] reveal that the well-known transition in which the domain wall passes from Bloch type to Néel type takes place in a critical thickness range between 100 and 50 nm.…”

“…Generally, the domain wall assumes the form of Bloch wall (in which an out-of-plane stray field exists in the domain wall due to the rotation of magnetic moments occurs in a perpendicular direction from the adjacent domains) when the film is thicker; and it will become Néel wall (in which the magnetic moments inside the wall strictly lie in the film plane, thus reducing the magnetostatic contribution to the wall energy) when the film thickness is below a critical value 14,15,[61][62][63] . Actually, classical books 14,15 and reports addressing theoretically and experimentally the stability of DW in films [61][62][63][64][65][66][67] reveal that the well-known transition in which the domain wall passes from Bloch type to Néel type takes place in a critical thickness range between 100 and 50 nm. Hence, we understand that deviations from the critical behavior observed for the thickest films may be ascribed to the thickness, i.e., the smaller geometrical dimension of the system.…”