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H. Navarro

Publications and source records attributed to H. Navarro.

6 recordsLinked to original sources
arXiv2023

Unusual magnetic hysteresis and transition between vortex to double pole states arising from interlayer coupling in diamond shaped nanostructures

Controlling the magnetic ground states at the nanoscale is a long-standing basic research problem and an important issue in magnetic storage technologies. Here, we designed a nanostructured material that exhibits very unusual hysteresis loops due to a transition between vortex and double pole states. Arrays of 700 nm diamond-shape nanodots consisting of Py(30 nm)/Ru(tRu)/Py(30 nm) (Py, permalloy (Ni80Fe20)) trilayers were fabricated by interference lithography and e-beam evaporation. We show that varying the Ru interlayer spacer thickness (tRu) governs the interaction between the Py layers. We found this interaction mainly mediated by two mechanisms: magnetostatic interaction that favors antiparallel (antiferromagnetic, AFM) alignment of the Py layers and exchange interaction that oscillates between ferromagnetic (FM) and AFM couplings. For a certain range of Ru thicknesses, FM coupling dominates and forms magnetic vortices in the upper and lower Py layers. For Ru thicknesses at which AFM coupling dominates, the magnetic state in remanence is a double pole structure. Our results showed that the interlayer exchange coupling interaction remains finite even at 4 nm Ru thickness. The magnetic states in remanence, observed by Magnetic Force Microscopy (MFM), are in good agreement with corresponding hysteresis loops obtained by Magneto-Optic Kerr Effect (MOKE) and micromagnetic simulations.

cond-mat.mes-hall↗
arXiv2020

Josephson coupling in high-T$_c$ superconducting junctions using ultra-thin BaTiO$_3$ barriers

We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa$_2$Cu$_3$O$_{7-d}$ electrodes and a BaTiO$_3$ barrier with thicknesses between 1 nm and 3 nm. The junctions with an area of 20 mm x 20 mm were fabricated combining optical lithography and ion etching using GdBa$_2$Cu$_3$O$_{7-d}$ (16 nm) / BaTiO$_3$ (1 - 3 nm) / GdBa$_2$Cu$_3$O$_{7-d}$ (16 nm) trilayers growth by sputtering on (100) SrTiO$_3$. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO$_3$ barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO$_3$. The Josephson coupling temperature is strongly reduced for increasing barrier thicknesses, which may be related to the suppression of the superconducting critical temperature in the bottom GdBa$_2$Cu$_3$O$_{7-d}$ due to stress. The Josephson energies at 12 K are of $\approx$ 1.5 mV and $\approx$ 7.5 mV for BaTiO$_3$ barriers of 1 nm and 2 nm. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-T$_c$ electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors.

cond-mat.supr-con↗
arXiv2019

Improving the Josephson energy in High-T$_c$ superconducting junctions for ultra-fast electronics

We report the electrical transport in vertical Josephson tunnel junctions (area 400 $μm$$^2$) using GdBa$_2$Cu$_3$O$_7$$_{-δ}$ electrodes and SrTiO$_3$ as an insulating barrier (with thicknesses between 1 nm and 4 nm). The results show Josephson coupling for junctions with SrTiO$_3$ barriers of 1 nm and 2 nm. The latter displays a Josephson of 8.9 mV at 12 K. This value is larger than the usually observed in planar arrays of junctions. Our results are promising for the development of superconducting electronic devices in the terahertz regime.

cond-mat.supr-con↗
arXiv1995

Star formation in normal and barred cluster spirals

An objective prism H alpha survey has shown that there is a population of early type spiral galaxies in nearby clusters with strong central bursts of star formation which could be due to galaxy--galaxy tidal interactions. Such galaxies are rarely found in the field.

astro-ph↗