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Porto, Portugal

Pereira A.M.,IFIMUP Unit | Soares J.C.,IFIMUP Unit | Ventura J.,IFIMUP Unit | Sousa J.B.,IFIMUP Unit | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2010

We developed a two dimensional transient numerical model that solves the first step of heat transfer of an active magnetic regenerative refrigerator (AMR) using the heat conduction equation for an adiabatic system. For micro-refrigeration, an AMR device is constituted by a magnetic material, placed on a silicon wafer containing micro-channels where a heat exchanging fluid flows. The magnetic materials used in the simulations are the promising the Gd 5Si 2Ge 2, La(Fe 0 88 Si 0.22) 13 and La 0.66Sr 0 33MnO 3 compounds, because they exhibit a giant magnetocaloric effect near room temperature. We considered different initial conditions, namely different micro-channel shapes, sizes and separations, aiming to increase the performance of the micro-cooler device. The influence of the thickness of the magnetic material on refrigeration power is also studied. Copyright © 2010 American Scientific Publishers All rights reserved. Source


Ventura J.,IFIMUP Unit | Teixeira J.M.,IFIMUP Unit | Araujo J.P.,IFIMUP Unit | Sousa J.B.,IFIMUP Unit | And 5 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2010

Magnetic tunnel junctions (MTJs) with thin barriers are already used as read sensors in recording media. However, the presence of pinholes across such few Å thick barriers cannot be excluded and one needs to investigate their effect on the MTJ-transport properties. By applying large electrical currents we could change the electrical resistance of the studied MgO MTJs (due to pinhole-size variations), and study how pinholes influence the barrier parameters (thickness t and height φ) obtained by fitting current-voltage characteristics to Simmons' model. We found that, with decreasing resistance, the barrier thickness (height) decreases (increases). These results were well reproduced by a model of parallel-resistances, allowing us to estimate pinhole-free barrier parameters. Copyright © 2010 American Scientific Publishers All rights reserved. Source

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