Bloch point nanospheres for the design of magnetic traps

Abstract

Through micromagnetic simulations, this work analyzes the possibility of using an array of magnetic nanospheres hosting Bloch points (BPs) to compose a system with the features of a magnetic trap (MT). We show that a BP can be nucleated as a metastable configuration in a wide range of the nanosphere radius compared to a quasi-uniform and vortex state. We also show that the stabilized BP generates a quadrupolar magnetic field outside the nanosphere. Based on this fact, we analyze the field profile of different arrays of these nanospheres, showing that the obtained magnetic field profiles share the needed features to compose MTs. Some highlights of using an array of Bloch point nanospheres in MTs rely on the magnetic field gradients achieved, which are orders of magnitude higher than similar standard systems, and allow three-dimensional trapping. Our results could be useful in trapping particles through the intrinsic magnetization of ferromagnetic nanoparticles while avoiding the commonly used mechanisms associated with Joule heating.

Symmetry Breaking-Induced Resonance Dynamics in Bloch Point Nanospheres: Unveiling Magnetic Volume Effects and Geometric Parameters for Advanced Applications in Magnetic Sensing and Spintronics

“…The controlled emission of radio frequency signals supports our proposal as a promising candidate for future magnonic devices. Additionally, given the capability of BP nanospheres to interact and form ordered arrays, our findings suggest that the proposed system could serve as a platform for 3D magnonic crystals with reconfigurable properties, including frequency and amplitude of oscillations.…”

“…Specifically, it was demonstrated that utilizing the demagnetizing field originating from an ordered array of BP nanospheres has significant applications in designing nanoscale magnetic traps. 43 Recently, the propagation of BPs through the application of electrical current was proposed, demonstrating the suppression of the unwanted topological Hall effect present in skyrmion systems. 28 Note that a crucial aspect of stabilizing BPs lies in their geometrical confinement.…”

“…For instance, the nucleation and stabilization of BPs in bilayer-like systems with opposite signs of Dzyaloshinskii–Moriya interaction have been studied through micromagnetic simulations. ,, Similarly, some of us have studied the demagnetizing field generated by a BP nanosphere and explored its consequences on the interaction with other BPs and potential applications. Specifically, it was demonstrated that utilizing the demagnetizing field originating from an ordered array of BP nanospheres has significant applications in designing nanoscale magnetic traps . Recently, the propagation of BPs through the application of electrical current was proposed, demonstrating the suppression of the unwanted topological Hall effect present in skyrmion systems .…”

“…We specifically introduced geometric asymmetries by exploring BPs confined in magnetic nanospheres from which we extracted sections (planes) of the sphere, as depicted in Figure . The choice of such geometry is manifold: first, several reports on BP stabilization in spherical geometries allow us to safely establish a BP as (at least) a metastable state. ,,,,, Second, asymmetric nanospheres are likely easier to synthesize experimentally than perfectly symmetric ones, thus approaching a more feasible experimental realization of our system. Also, there is experimental evidence of BP-like structures in spherical nanoparticles .…”

Giant supermagnonic Bloch point velocities in cylindrical ferromagnetic nanowires

“…In finite nanostructures such as magnetic spheres, it is characterized by the non-zero and not integer 3D topological charge due to a variable helicity arising from magnetostatic energy minimization, 21 configuring magnetic fields with a quadrupolar nature, 22 which could be used in technological applications. 23 It was predicted that BP has a large mobility in response to external driving magnetic field. 24 Recent numerical simulations reported the BP-DW velocity in permalloy cylindrical nanowire circa 1 km s −1 , slightly higher than the magnon group velocity.…”