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Yahyaoui S.,University of Monastir | Khalfaoui M.,University of Monastir | Kallel S.,University of Monastir | Kallel N.,University of Monastir | And 4 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2015

We report a study on the magnetic properties of the (La0.56Ce0.14)Sr0.30MnO3 perovskite, by a mean-field method. By scaling of the experimental magnetization data, the mean-field exchange parameter λ and the BS function of the equation of state BS[(H+Hexch)/T] are directly determined, as well as the order of the phase transition. The spin quantum number of the manganite has been also determined. The mean-field scaling has been used to estimate magnetic entropy change (-ΔSM) within the thermodynamics of the model and without using the usual numerical integration of a Maxwell relation. The maxima of the positive absolute value of (-ΔSM) upon variation of the applied magnetic field at 1 and 5 T are about 1.68 and 5.04 J kg-1 K-1, respectively. Satisfactory agreement between the mean-field model and experimental behavior has been found. © 2015 Elsevier B.V. All rights reserved. Source


Yahyaoui S.,University of Monastir | Khalfaoui M.,University of Monastir | Kallel S.,University of Monastir | Kallel N.,University of Monastir | And 4 more authors.
Journal of Alloys and Compounds | Year: 2016

We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to justify the magnetocaloric effect (MCE) on La0.7Sr0.3Mn0.9Ti0.1O3. The modeling the magnetic properties of the La0.7Sr0.3Mn0.9Ti0.1O3 was investigated. Using the Brillouin function we have determined the mean field exchange parameter λ and the total angular momentum J of the perovskite. The mean-field equation of state leads the system to second order ferromagnetic (FM)-paramagnetic (PM) phase transition. The expressions describing entropy and its change under the influence of magnetic field have been derived. A large magnetic entropy (-ΔSM) has been observed in our sample with a peak centered on the Curie temperature (TC = 210 K). The theoretical calculations are compared with experimental behavior. © 2016 Elsevier B.V. All rights reserved. Source


Leite I.T.,INESC Porto | Hierro-Rodriguez A.,INESC Porto | Hierro-Rodriguez A.,IFIMUP and in Institute of Nanoscience and Nanotechnology | Silva A.O.,INESC Porto | And 10 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2013

This Letter reports on the assembly on the tip of an optical fibre of a metamaterial film fabricated by a self-assembly bottom-up method, composed of silver nanowires embedded in an alumina matrix. By illuminating the film through the fibre in a reflection configuration, we observe experimentally the optical response of the metamaterial in agreement with theoretical predictions and interpreted as the excitation of surface plasmon-polaritons in the cylindrical surface of the nanowires. These results pave the way for low-cost optical fibre devices that incorporate metamaterial films. Micrographs of a nanowire metamaterial film mounted on the tip of an optical fibre (left) and top-view of the sample in a transmission configuration (right). The red colour results from the absorption of the other optical wavelengths by the plasmon modes in the metamaterial. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Silva D.J.,IFIMUP and in Institute of Nanoscience and Nanotechnology | Bordalo B.D.,IFIMUP and in Institute of Nanoscience and Nanotechnology | Pereira A.M.,Imperial College London | Ventura J.,IFIMUP and in Institute of Nanoscience and Nanotechnology | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2014

Magnetic refrigeration is an alternative cooling technique with envisaged technological applications on micro- and opto-electronic devices. Here, we present a magnetic micro-refrigerator cooling device with embedded micro-channels and based on the magnetocaloric effect. We studied the influence of the coolant fluid in the refrigeration process by numerically simulating the heat transfer processes using the finite element method. This allowed us to calculate the cooling power of the device. Our results show that gallium is the most efficient coolant fluid and, when used with Gd5Si 2Ge2, a maximum power of 11.2 W/mm3 at a working frequency of ∼5 kHz can be reached. However, for operation frequencies around 50 Hz, water is the most efficient fluid with a cooling power of 0.137 W/mm3. Copyright © 2014 American Scientific Publishers All rights reserved. Source


Ventura J.,IFIMUP and in Institute of Nanoscience and Nanotechnology | Teixeira J.M.,IFIMUP and in Institute of Nanoscience and Nanotechnology | Paz E.,International Iberian Nanotechnology Laboratory | Amaral J.S.,IFIMUP and in Institute of Nanoscience and Nanotechnology | And 8 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2013

The exchange bias effect at the interface between antiferromagnetic (AFM) and ferromagnetic (FM) layers is of paramount importance in state-of-the-art spintronic devices. However, a complete account of the physics behind exchange bias remains elusive and new effects are constantly unraveled. In particular, a bimodal distribution of blocking temperatures $ (T_{\rm B})$ was recently discovered, associated with the bulk of the AFM layer and interfacial AFM/FM regions with spin-glass-like properties. Here we study exchange bias in MnIr (25, 60 Å)/CoFe (50 Å) bilayers annealed at high temperatures (623 K and 673 K). We observe, for all samples and annealing temperatures, the existence of a large exchange bias variation at low temperatures associated with interfacial disorder. Such variation is more significative in the thinnest samples, where it is found to be independent on annealing temperature. On the other hand, in the thickest samples the contribution of the low temperature distribution largely increases with annealing temperature, due to enhanced disorder arising from Mn diffusion. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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