Overcoming the Limits of Vortex Formation in Magnetic Nanodots by Coupling to Antidot Matrix

Abstract

Static magnetic configurations of thin circular soft (permalloy) magnetic nanodots, coupled to a hard antidot matrix with perpendicular magnetization, are studied by micromagnetic simulations. It is demonstrated, that dipolar fields of the antidot matrix promotes the formation of a magnetic vortex state in nanodots. The vortex is the dot ground state at zero external field in ultrathin nanodots with diameters as low as 60 nm, that is far beyond the vortex stability range in an isolated permalloy nanodot. Depending on the geometry and antidot matrix material it is possible to stabilize either radial vortex state or unconventional vortices with the angle between in-plane magnetization and radial direction ψ = 0, π/2.

Micromagnetic Simulations of Submicron Vortex Structures for the Detection of Superparamagnetic Labels

“…Typically, the free layer of a GMR element consists of a soft ferromagnetic material [ 35 ]. The formation of vortices in such submicron layers was theoretically and experimentally investigated in [ 36 , 37 , 38 , 39 ], showing that the formation of a vortex state highly depends on the aspect ratio of the layer. Ensuring a stable vortex appearance, this was complemented by Equation (3), which connects the layer thickness t L to the layer diameter d L and the exchange length of the material (l ex,L = √2A ex,L /µ 0 M s,L ²) [ 40 ].…”

Helicity of magnetic vortices and skyrmions in soft ferromagnetic nanodots and films biased by stray radial fields

“…The main idea of the stabilization of magnetic skyrmions and unconventional vortices in soft magnetic films and dots is the application of magnetic fields having radial symmetry [43,44]. Here we describe one possible approach, which, with some modifications, allows us to achieve stabilization of both vortices and skyrmions.…”

“…Magnetization configuration of the soft magnetic dot (layer) depends on the geometry of both the dot (layer) and the antidot matrix. One can achieve a quasisingle domain state, a vortex (skyrmion) state, or more complex magnetization configurations by varying the geometric parameters [43,44]. In Fig.…”

“…Recently, we have proposed an alternative method for the stabilization of magnetic skyrmions and vortices [43,44]. It is based on the exploiting of the radial magnetic field, which could be created, e.g., by an antidot matrix.…”

“…Simultaneously, in the application to soft magnetic nanodots, radial stray fields from an antidot matrix allow for significant reduction of the minimal size and thickness of dots, where magnetic vortices can be stabilized in Ref. [43].…”