Navegando por Autor "Melo, Winder Alexander de Moura"
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Item Emergence and mobility of monopoles in a unidirectional arrangement of magnetic nanoislands.(2015) Loreto, Renan Pires; Morais, L. A.; Melo, Winder Alexander de Moura; Pereira, Afranio Rodrigues; Silva, R. C.; Nascimento, Fábio Santos; Mól, Lucas Alvares da SilvaMagnetricity, the magnetic equivalent of electricity, was recently verified experimentally for the first time. Indeed, like the stream of electric charges that produces electric current, emergent magnetic monopoles have been observed to roam freely in geometrically frustrated magnets known as spin ice. However, such phenomena demand extreme physical conditions, say, a single spin ice crystal has to be cooled to very low temperature, around 0.36 K. Candidates to overcome this difficulty are their artificial analogues, the so-called artificial spin ices. Here, we demonstrate that a specific unidirectional arrangement of nanoislands yields a peculiar system where magnetic monopoles emerge and are constrained to move along aligned dipoles, providing an ordered flow of magnetic charges at room temperature.Item Magnetic vortex crystal formation in the antidot complement of square artificial spinice.(2014) Araujo, Clodoaldo Irineu Levartoski de; Silva, Rodrigo da Costa; Ribeiro, Igor Renato Bueno; Nascimento, Fábio Santos; Felix, Jorlandio Francisco; Ferreira, Sukarno Olavo; Mól, Lucas Alvares da Silva; Melo, Winder Alexander de Moura; Pereira, Afranio RodriguesItem Realization of rectangular artificial spin ice and direct observation of high energy topology.(2017) Ribeiro, Igor Renato Bueno; Nascimento, Fabio Santos; Ferreira Junior, Silvio da Costa; Melo, Winder Alexander de Moura; Costa, C. A. R.; Borme, J.; Freitas, Paulo Peixeiro; Wysin, G. M.; Araujo, Clodoaldo Irineu Levartoski de; Pereira, Amanda RaimundiIn this work, we have constructed and experimentally investigated frustrated arrays of dipoles forming two-dimensional artificial spin ices with different lattice parameters (rectangular arrays with horizontal and vertical lattice spacings denoted by a and b respectively). Arrays with three different aspect ratios γ = a/b = 2, 3 and 4 are studied. Theoretical calculations of low-energy demagnetized configurations for these same parameters are also presented. Experimental data for demagnetized samples confirm most of the theoretical results. However, the highest energy topology (doubly-charged monopoles) does not emerge in our theoretical model, while they are seen in experiments for large enough γ. Our results also insinuate that the string tension connecting two magnetic monopoles in a pair vanishes in rectangular lattices with a critical ratio γ = γc = 3, supporting previous theoretical predictions.