Browsing by Author "Nunez, Alvaro S."

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    A three step recipe for designing auxetic materials on demand
    (2022) Acuna, Daniel; Gutierrez, Francisco; Silva, Rodrigo; Palza, Humberto; Nunez, Alvaro S.; During, Gustavo
    Auxetics are an unusual family of materials that, for instance, when stretched in a particular direction will exhibit an expansion of the dimensions that are perpendicular to the applied stress; however, despite many known examples of auxectics there is no universal description of the material properties. Here, the authors report a model based on antiferromagnetic spins and demonstrate how this can be used to design a auxetic material with a Poisson ratio of -1 over a range of finite strain.
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    Magnetostatic interaction between Bloch point nanospheres
    (2023) Zambrano-Rabanal, Cristobal; Valderrama, Boris; Tejo, Felipe; Elias, Ricardo Gabriel; Nunez, Alvaro S.; Carvalho-Santos, Vagson L.; Vidal-Silva, Nicolas
    Three-dimensional topological textures have become a topic of intense interest in recent years. This work uses analytical and numerical calculations to determine the magnetostatic field produced by a Bloch point (BP) singularity confined in a magnetic nanosphere. It is observed that BPs hosted in a nanosphere generate magnetic fields with quadrupolar nature. This finding is interesting because it shows the possibility of obtaining quadrupole magnetic fields with just one magnetic particle, unlike other propositions considering arrays of magnetic elements to generate this kind of field. The obtained magnetostatic field allows us to determine the interaction between two BPs as a function of the relative orientation of their polarities and the distance between them. It is shown that depending on the rotation of one BP related to the other, the magnetostatic interaction varies in strength and character, being attractive or repulsive. The obtained results reveal that the BP interaction has a complex behavior beyond topological charge-mediated interaction.
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    Stability Enhancement by Zero-Point Spin Fluctuations: A Quantum Perspective on Bloch Point Topological Singularities
    (2024) Tapia, Alonso; Saji, Carlos; Roldan-Molina, Alejandro; Nunez, Alvaro S.
    Bloch points represent singularities within magnetic materials. From a macroscopic viewpoint, their cores are points where the magnetization vector is undefined, resulting in unique topological characteristics that influence the magnetic behavior of their hosts. The picture is very different at the microscopic level, where quantum effects enter the scene. The spin variables' quantum dynamics effect on the BP's stability is revealed. Zero-point fluctuations, intrinsic fluctuations within the quantum mechanical ground state originating from the uncertainty principle, play a fundamental role. It is found that quantum fluctuations bloom in the vicinity of the singularity, thereby reducing the effective magnetic moment in its neighborhood. This increases the overall stability of the BP. These methods also allow for a characterization of the magnonic eigenmodes surrounding and bound to the singularity. The latter leads to predict on quite general grounds several features of the magnonic spectra, its degeneration structure, and its splitting response under a magnetic field. The last result is coherent with the association of a magnetic moment to the orbital angular momentum of the magnons. This approach allows integration with multiscale algorithms to provide a realistic description of generic topological singularities.