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Your search keyword '"Vélez, M."' showing total 14 results
Start Over Author "Vélez, M." Journal nanotechnology
14 results on '"Vélez, M."'

12. Temperature dependence of the magnetization reversal process in patterned Ni nanowires

Author

Pérez-Junquera, A, Martín, J I, Vélez, M, Alameda, J M, and Vicent, J L

Abstract

The magnetic behaviour of patterned Ni wires has been studied by magnetotransport measurements to analyse the mechanisms that govern the magnetization reversal in these ordered nanostructures as a function of temperature in the 150–350 K range. These results show reversal processes driven by a temperature-dependent combination of two different mechanisms: coherent rotation and a curling-like irreversible process. When the field is decreased from saturation the magnetization rotates reversibly until it reaches the nanowires&rquot; direction where it reverses its sign by an irreversible process at low fields. The amplitude in the magnetoresistance of this irreversible process is reduced as the temperature is increased, with a sharp step at room temperature. In fact, the analysis of the angular dependence reveals that it is compatible with an incoherent curling process up to 300 K in the whole angular range. For higher temperatures, a crossover towards coherent rotation is observed in the irreversible contribution for high angles between the applied field and the wire direction.

Published
2003

13. Chiral asymmetry detected in a 2D array of permalloy square nanomagnets using circularly polarized x-ray resonant magnetic scattering.

Author

Díaz J, Gargiani P, Quirós C, Redondo C, Morales R, Álvarez-Prado LM, Martín JI, Scholl A, Ferrer S, Vélez M, and Valvidares SM

Abstract

The sensitivity of circularly polarized x-ray resonant magnetic scattering (CXRMS) to chiral asymmetry has been demonstrated. The study was performed on a 2D array of Permalloy (Py) square nanomagnets of 700 nm lateral size arranged in a chess pattern, in a square lattice of 1000 nm lattice parameter. Previous x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) images on this sample showed the formation of vortices at remanence and a preference in their chiral state. The magnetic hysteresis loops of the array along the diagonal axis of the squares indicate a non-negligible and anisotropic interaction between vortices. The intensity of the magnetic scattering using circularly polarized light along one of the diagonal axes of the square magnets becomes asymmetric in intensity in the direction transversal to the incident plane at fields where the vortex states are formed. The asymmetry sign is inverted when the direction of the applied magnetic field is inverted. The result is the expected in the presence of an unbalanced chiral distribution. The effect is observed by CXRMS due to the interference between the charge scattering and the magnetic scattering.

Published
2020
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14. Patterning of rutile TiO2 surface by ion beam lithography through full-solid masks.

Author

Sanz R, Jaafar M, Hernández-Vélez M, Asenjo A, Vázquez M, and Jensen J

Abstract

In this work we present and discuss the nanopatterning of rutile TiO(2) single crystal surfaces following their irradiation with energetic heavy ions through a stencil mask of Ni filled self-ordered porous anodic alumina. After etching in HF a corrugated surface morphology is obtained composed of parallel alternate furrows and ridges (or nanobars) 50 nm in diameter and with 100 nm pitch. In addition, isolated, but collapsed, TiO(2) nanorods are seen lying on the patterned surface. The stability of the nanopatterned surface under high temperatures treatments and crystalline properties are analyzed.

Published
2010
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