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Physica B Condensed Matter 04/2013; · 1.06 Impact Factor
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ABSTRACT: Magnetic [FeNi (170 nm)/Ti (6 nm)]3/Cu (L(cu) = 250 or 500 nm)/[Ti (6 nm)/FeNi (170 nm)]3 multilayers were designed with focus on high frequency applications. They were deposited onto glass or a microfluidic system compatible flexible Ciclo Olefin Copolymer substrate and comparatively tested. A maximum sensitivity for the total impedance of 110%/Oe was obtained for a driving current frequency of 30 MHz for [FeNi/Ti]3/Cu (L(cu) = 500 nm)/[Ti/FeNi]3 multilayers deposited onto a glass substrate and 45%/Oe for a driving current frequency of 65 MHz for the same multilayers deposited onto the flexible polymer substrate, a very promising result for applications. The possibility of using flexible substrate/[FeNi/Ti],/Cu/[Ti/FeNi]3 multilayers as MI pressure-sensitive elements was also demonstrated.
Journal of Nanoscience and Nanotechnology 09/2012; 12(9):7496-500. · 1.56 Impact Factor
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ABSTRACT: Particulate composite films of poly(vinylidene fluoride) and CoFe2O4 and NiFe2O4 were prepared by solvent casting and melt processing. The well-dispersed ferrite nanoparticles nucleate the piezoelectric beta-phase of the polymer, but the different ferrites nucleate the whole polymer crystalline phase at different filler concentrations. The macroscopic magnetic and dielectric response of the composites demonstrates a strong dependence on the volume fraction of ferrite nanoparticles, with both magnetization and dielectric constant increasing for increasing filler content. The beta-relaxation in the composite samples is similar to the one observed for beta-PVDF obtained by stretching. A superparamagnetic behavior was observed for NiFe2O4/PVDF composites, whereas CoFe2O4/PVDF samples developed a hysteresis cycle with coercivity of 0.3T. (C) 2011 Elsevier B.V. All rights reserved.
Materials Chemistry and Physics 01/2012; 131(3):698-705. · 2.23 Impact Factor
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ABSTRACT: Magnetoelectric (ME) nanocomposite films composed of magnetostrictive CoFe2O4 nanoparticles with sizes between 35 and 55 nm embedded in P(VDF-TrFE) have been successfully prepared by a solvent casting method. The ferroelectric, piezoelectric, magnetic and ME properties of the nanocomposite and their variation with the wt% of the ferrite filler, thickness of the composite and direction of the applied magnetic field have been investigated.Ferroelectric and piezoelectric properties were improved when a small amount of ferrite nanoparticles was added to the polymeric matrix. Magnetic properties vary linearity with ferrite content. The highest ME response of 41.3 mV cm−1 Oe−1 was found in the composite with 72 wt% when a 2.5 kOe DC field was transversely applied to the sample surface. This value is among the highest reported in two phase particulate polymer nanocomposites. Thickness of the composite has no influence in the ME response, allowing tailoring sensor thickness for specific applications. The good value of the ME coefficient and the flexibility of the films make these composites suitable for applications in ME smart devices.
Journal of Physics D Applied Physics 11/2011; 44(49):495303. · 2.54 Impact Factor
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ABSTRACT: Tensile stress-strain behavior of Ni57.5Mn22.5Ga20.0 single crystal
exhibiting a high-temperature 2M-martensitic phase stable up to 360\degree C
has been studied in the course of thermal and mechanical cycling. The
ultra-large reversible strains, about 9%, caused by the shape memory and
superelasticity effects, have been observed up to 400 \degree C being the
instrumental temperature limit. Abnormally large two-way shape memory effect
with 9% of strain magnitude has been found. The cycling procedure and the
variation of thermal/mechanical routs of the training of samples revealed the
destabilization (rejuvenation) of martensite. This physical effect is opposite
to the well-known phenomenon of martensite stabilization. A destabilization
effect is explained phenomenologically in terms of internal stressing of the
alloy sample by the crystal defects.
01/2011;
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ABSTRACT: Magnetic properties and the magnetoimpedance (MI) effect were studied for a series of [ Fe <sub>20</sub> Ni <sub>80</sub>/ Ti ]<sub> n </sub>/ Fe <sub>20</sub> Ni <sub>80</sub> ( n =0 to 5) nanostructures, prepared by dc magnetron sputtering. The thickness of the FeNi layers was selected as 170 nm in order to avoid the appearance of the “transcritical” state that takes place for thicker layers. First, the influence of the Ti layer thickness was determined for n =1 trilayers, with Ti layers ranging from 2 to 20 nm. The minimum coercivity corresponded to a Ti layer of about 6 nm. Second, the magnetic properties and MI responses were studied for different [ FeNi / Ti ]<sub> n </sub>/ FeNi structures at a fixed Ti layer thickness of 6 nm. The complex impedance was measured for a frequency range of 1–300 MHz. The highest value of the MI was obtained in the sample [ FeNi / Ti ]<sub>5</sub>/ FeNi with the largest total thickness.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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ABSTRACT: The performance of the magnetoimpedance effect in terms of magnitude and sensibility is evaluated for two FeNi/Cu/FeNi multilayer structures with different geometries, such that in one of them the magnetic layers are in contact at the edges, presenting a closed magnetic path that is absent in the other. Magnetization measurements by Kerr effect and magnetic domain observations are used to characterize the samples. The results show that the sample with the closed magnetic path performs better, reaching a value of 38 % of variation of the impedance and a sensibility of about 5%/Oe at 325 MHz. However, at lower frequencies the sample with open magnetic path presents higher values of the magnetoimpedance effect and its sensitivity than the one with the closed magnetic path. Finite element simulations confirm that this behavior is a direct consequence of the geometry of the samples.
IEEE Transactions on Magnetics 03/2010; · 1.36 Impact Factor
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ABSTRACT: Various series of permalloy thin films were grown by dc-sputtering on Si (100) and glass substrates at room temperature and different argon pressure values using a Fe<sub>20</sub> Ni<sub>80</sub> target. The increase of argon pressure leads to a decrease of the Fe concentration in the films from 17 at.% to 15 at.%, an increase of the root mean square roughness of film surfaces, and a decrease of the sharpness of the crystalline texture of the samples. The increase of the film thickness leads to an increase of the coercive field. The transition to the "transcritical" state was observed at a critical thickness that decreases from 220 to 50 nm as the argon pressure in the chamber increases. This state was confirmed by the characteristic shapes of hysteresis loops, rotatable magnetic anisotropy, and the appearance of stripe domains.
IEEE Transactions on Magnetics 03/2010; · 1.36 Impact Factor
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ABSTRACT: Ferromagnetic resonance was used to study the influence of temperature and film thickness on magnetic properties of Ni–Mn–Ga films deposited on single crystal MgO(001) substrates. It has been shown that depending on the film thickness and preparation condition, three configurations of magnetic anisotropy can be realized in these films. The temperature dependence of the anisotropy field is determined.
Applied Physics Letters 02/2010; · 3.84 Impact Factor
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ABSTRACT: A Multilayer Magnetoimpedance sensor composed by the following layers: Fe19Ni81(150 nm)/Cu(500 nm)/Fe19Ni81(150 nm), has been developed for non-destructive testing of ferromagnetic objects. Iron plates of different width have been tested in a frequency range around 100 MHz. Sensitive parameters that can be used for recognition of ferromagnetic objects are: maximum value, characteristic fields (maximum, minimum and folding points) and hysteresis of the Magnetoimpedance. These parameters can be followed in the total impedance curves, or separately in the real and imaginary components. The most accurate results for the iron plate width detection were obtained using the total impedance variation.
Sensor Letters 05/2009; 7(3):374-377. · 0.82 Impact Factor
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ABSTRACT: Extensive measurements of the temperature dependencies of resistivity under constant magnetic fields made it possible to clarify the premartensitic transition sensitivity to applied magnetic field up to 14 T in polycrystalline and monocrystalline Ni–Mn–Ga alloys with compositions close to the stoichiometric one. A low-field minimum on the transition temperature versus magnetic field curves is found in both alloys. This minimum is attributed to the magnetic anisotropy contribution to the Clausius–Clapeyron relationship, which describes the premartensitic transition. This contribution is confirmed by magnetization loops measurements.
Applied Physics Letters 02/2009; 94(5):051909-051909-3. · 3.84 Impact Factor
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ABSTRACT: Several composites, with outstanding magnetostrictive properties, have been synthesized combining a polyurethane elastomer with polycrystalline powders of Terfenol-D. A preferential orientation of the latter was obtained by curing the material in a magnetic field. The morphology of the polymeric matrix can be modified by changing the hard/soft segment ratio of the polyurethane. The influence of the morphology of the polymeric matrix on the composite response has been studied, by following the storage modulus, E′, by DMTA technique. The magnetostrictive response has been studied as a function of the Terfenol-D particle size distribution, and the content of magnetostrictive particles in the composite. The highest response (about 1390ppm) was obtained for a composite having polyurethane with a 1.5 hard to soft segment ratio, 50% weight of Terfenol-D of 212–300μm particle size, oriented in a magnetic field of 0.5T.
Sensors and Actuators A-physical - SENSOR ACTUATOR A-PHYS. 01/2009; 149(2):251-254.
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ABSTRACT: Longitudinal and transverse magnetoimpedance is studied for Fe<sub>19</sub>Ni<sub>81</sub> (150 nm)/Cu(500 nm)/Fe<sub>19</sub>Ni<sub>81</sub> (150 nm) multilayered structures with exactly the same geometry, having either longitudinal or transverse magnetic anisotropy, at frequencies up to 500 MHz, convenient enough for technological applications. The highest sensitivity was observed for longitudinal magnetoimpedance of the structures with transverse magnetic anisotropy. Transverse magnetoimpedance ratio for structures with transverse magnetic anisotropy was small but transverse magnetoimpedance and its sensitivity for the structures with longitudinal magnetic anisotropy was quite high. Relatively high values of transverse and longitudinal magnetoimpedance for the structures with longitudinal anisotropy lead to the possibility to design a single sensitive element detector for the control of the magnetic fields, parallel and perpendicular to the element.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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ABSTRACT: Magnetic, micromagnetic, and texture properties of the martensitic thin films prepared by magnetron sputtering of Ni<sub>49.5</sub>Mn<sub>28</sub>Ga<sub>22.5</sub> target on MgO(100) wafer are studied as a function of film thickness. The films exhibit 220-fiber texture. Moreover, in contrast to thick films, a considerable in-plane texture component is giving rise to the pronounced in-plane magnetic anisotropy found in the thin film. The texture features together with a large magnetocrystalline anisotropy lead to the particular domain structure and different magnetic anisotropy components of films depending on the film thickness and substrate nature.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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ABSTRACT: In recent years, one of the most promising new actuator technologies is based on the use of Shape Memory Alloys (SMA). The
main challenge for the application of devices that use these materials is the hysteresis in the phase transition they suffer
during actuation. Finite element analysis (FEA) is an important aid in the simulation of mechanical properties and thermal
fields in actuators. Dynamic simulations give in many cases enough information without the necessity of building a prototype.
We have used ABAQUS to simulate a Nitinol wire used in a micropositioning actuator. The model parameters, not given by the
supplier but required by the FEA program, have been obtained by thermal and mechanical characterization of the material used.
The output force is computed and compared with the measurements.
The European Physical Journal Special Topics 04/2008; 158(1):39-44. · 1.56 Impact Factor
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ABSTRACT: The use of ferromagnetic shape memory alloy (FSMA) particles as fillers in polymeric matrix composites has been proposed for vibration damping. The large pseudo-plastic recoverable deformation of the FSMA particles due to the rearrangement of twin variants can dissipate a large amount of energy, both under compression and tension. The composites studied are made by mixing particles of NiMnGa with a polyurethane matrix. A magnetic field is applied to the composite while the matrix sets, to achieve a strong [112] texture in the field direction. In situ strobed neutron diffraction measurements were carried out while the composites were subjected to a cyclic deformation. They show that the intensity of certain peaks varies during the deformation cycle. All the peaks that show this behavior can be grouped into pairs that stem from a single austenitic peak. The (020) and (112) martensite peaks correspond to the splitting of the (220) austenite peak, and the intensity of one increases as that of the other decreases. The neutron measurements show directly that there is a change in the texture of the composite during the stress cycle applied to the composite and confirm that the large mechanical loss observed in the stress–strain cycles is in good part due to the rearrangement of twin variants in the FSMA filler used in the composites.
Journal of Physics Condensed Matter 02/2008; 20(10):104247. · 2.55 Impact Factor
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ABSTRACT: Based on magnetic measurements, a modulated structure, as occurring in spinodal decomposition, has recently been suggested to exist in mechanically alloyed Fe-50 at.%Cu solid solutions after certain heat treatments. In this work, clear microstructural evidence of the modulated structure is obtained from transmission electron microscopy.
EPL (Europhysics Letters) 07/2007; 32(7):585. · 2.17 Impact Factor
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ABSTRACT: We report the magnetic properties of Tb/Si multilayers obtained by rf-sputtering at the Tb layer thickness LTb = 3 nm. Analysis of the magnetization processes indicates more complex behaviour than canonical spin-glass transition. It is more probable that these multilayers contain both Tb superparamagnetic particles and Tb–Si spin-glass alloys.
Chinese Physics Letters 06/2007; 24(6):1717. · 0.73 Impact Factor
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ABSTRACT: In ferromagnetic shape memory alloys the ferromagnetic domains are coupled to twin crystal variants present in the martensitic phase. These materials suffer rearrangements of the twin domains in the martensite state by applying a magnetic field, easily detectable on single crystal measurements both magnetically and by following the deformation, that can reach values up to 6-10%. In this work we have studied a polycrystalline alloy of composition Ni51Mn28Ga21 prepared by rapid quenching in the form of a ribbon. The hysteresis loop shows no coercitivity (Hc ≈ 0), but a change in the slope of the magnetization curve at a critical field, H*. This magnetization process seems to correspond to magnetic variant reorganization (de-twining) and moment rotations. H* is about 2 kOe at room temperature. It decreases as the temperature increases and disappears just upon crossing the austenite temperature. In order to confirm the correlation of the magnetic behaviour with the magnetic variant reorganization, strain measurements have been performed in a sandwich structure formed by two pieces of the ribbon enclosing a strain gauge and firmly glued to it. The critical field H* has been found to correlate with the change in the deformation of the ribbon. A change in slope is observed for H*, but the final strain is only about −20 × 10−6 in applied fields of 10 kOe. The amount of strain is very low as compared with the expected for de-twinning, but the correlation suggests the same mechanism is implied in both effects.
Sensor Letters 02/2007; 5(1):65-68. · 0.82 Impact Factor
