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Chernenko V.A.,University of the Basque Country | Chernenko V.A.,Ikerbasque | Barandiaran J.M.,University of the Basque Country | L'Vov V.A.,Institute of Magnetism | And 3 more authors.
Journal of Alloys and Compounds | Year: 2013

The transformation-induced strains with and without applied magnetic field and magnetostriction loops at different temperatures have been measured for polycrystalline ferromagnetic and metamagnetic shape memory Heusler alloys such as NiMnGa, NiFe(Co)Ga and NiMnSn, respectively. The results evidence a magnetic field oriented growth of martensitic variants during the martensitic transformation in NiMnGa sample, whereas this effect is not evident in the other two alloys. In the NiMnSn alloy, the isotropic volume magnetostriction dominates the anisotropic domain magnetostriction. © 2012 Elsevier B.V.


Barandiaran J.M.,University of the Basque Country | Chernenko V.A.,University of the Basque Country | Chernenko V.A.,Ikerbasque | Gutierrez J.,University of the Basque Country | And 2 more authors.
Applied Physics Letters | Year: 2012

We report parallel and perpendicular magnetostriction measurements performed in polycrystalline Ni 2MnGa to shed light on the magnetoelastic coupling, responsible for the ordinary magnetostriction, and giant magnetic field-induced strains (MFIS). Parallel magnetostriction is negative while its perpendicular component switches from positive to negative at the martensitic transformation. The saturation magnetostriction is negative, takes moderate values and has a large increase in absolute value at both pre- and martensitic temperatures, arising from the lattice softening at the transitions. The reported values are those of the true magnetostriction and can be a starting point for further studies of MFIS. © 2012 American Institute of Physics.


Chernenko V.A.,University of the Basque Country | Chernenko V.A.,Ikerbasque | Barandiaran J.M.,University of the Basque Country | Rodriguez Fernandez J.,University of Cantabria | And 4 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2012

The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni 2Mn 1.4Sn 0.6 Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to Θ D=310±2 K and γ= 16.6±0.3 mJ/K 2mol, respectively, do not depend on the magnetic field. © 2012 Elsevier B.V.


Aseguinolaza I.R.,University of the Basque Country | Orue I.,SGiker | Svalov A.V.,University of the Basque Country | Chernenko V.A.,University of the Basque Country | And 3 more authors.
Journal of Materials Science | Year: 2012

Epitaxial Ni-Mn-Ga films have been grown onto heated substrates by sputtering. Their chemical composition depends on the sputtering argon pressure. Representative epitaxial films of Ni 52.3Mn 26.8Ga 20.9, 0.5 μm-thick, transform martensitically at about 120 °C, accompanied by sharp changes in the lattice parameter and resistivity, and orders ferromagnetically below 98°. The observed high transformation temperature, orthorhombic martensitic structure, twinning mode and film morphology, indicate a potential multifunctional behavior of the film, such as high-temperature shape-memory effect and magnetic field actuation. © 2011 Springer Science+Business Media, LLC.


Lazpita P.,University of the Basque Country | Chernenko V.A.,University of the Basque Country | Chernenko V.A.,Ikerbasque | Barandiaran J.M.,University of the Basque Country | And 4 more authors.
Materials Science Forum | Year: 2010

A Mn-enriched Ni46.4Mn32.8Sn20.8 Heusler alloy has been prepared by the induction melting and casting method. The samples used were annealed at 900°C during 72 h with a subsequent water quench. The magnetostructural transformation (MST) in the vicinity of Tm=230K and Ta=250K has been found, and characterized by DSC, magnetization and resistivity measurements. Changes in the crystal structure due to the MST were observed using neutron diffraction at different temperatures. The crystal structure of martensitic phase shows a good fits to the 4-layered orthorhombic martensite with a Pmma space group. The linear shift of transformation temperatures was found in the entire high magnetic field range up 14T to be dTm/dB0 = -1.50 K/T and dTa/dB0 = -1.26 K/T, whereas in the low field range we found an increase of both characteristic temperatures. The entropy changes at the MST were evaluated using the Clausius-Clapeyron relationship. The transformation-induced magnetoresistance has been measured. © (2010) Trans Tech Publications.


Aseguinolaza I.R.,University of the Basque Country | Orue I.,SGiker | Svalov A.V.,University of the Basque Country | Wilson K.,Boise State University | And 4 more authors.
Thin Solid Films | Year: 2014

Ni-Mn-Ga thin films exhibiting a martensitic transformation (MT) overlapping with the Curie temperature have been sputter-deposited onto heated Si/SiNx substrates. The films had a partially oriented polycrystalline structure and the tetragonal 10 M-martensitic phase undergoing a reverse MT into cubic austenite between 57 and 156°C. The MT was studied with structural, substrate curvature, magnetic and resistivity methods. The substrate imposed residual stress which changes the sign of the transformation volume strain across MT. The role of the magnetocrystalline anisotropy and its impact on magnetic properties are interpreted in terms of film texture and film stiffness. © 2014 Elsevier B.V. All rights reserved.


Ahyayauch H.,University of the Basque Country | Ahyayauch H.,Institute Superieur Des Professions Infirmieres Et Des Techniques Of Sante | Sot J.,University of the Basque Country | Collado M.I.,SGiker | And 4 more authors.
Biophysical Journal | Year: 2015

Diacylglycerol (DAG)-induced activation of phosphatidylinositol-phospholipase C (PI-PLC) was studied with vesicles containing PI, either pure or in mixtures with dimyristoyl phosphatidylcholine, distearoyl phosphatidylcholine, sphingomyelin, or galactosylceramide, used as substrates. At 22°C, DAG at 33 mol % increased PI-PLC activity in all of the mixtures, but not in pure PI bilayers. DAG also caused an overall decrease in diphenylhexatriene fluorescence polarization (decreased molecular order) in all samples, and increased overall enzyme binding. Confocal fluorescence microscopy of giant unilamellar vesicles of all of the compositions under study, with or without DAG, and quantitative evaluation of the phase behavior using Laurdan generalized polarization, and of enzyme binding to the various domains, indicated that DAG activates PI-PLC whenever it can generate fluid domains to which the enzyme can bind with high affinity. In the specific case of PI/dimyristoyl phosphatidylcholine bilayers at 22°C, DAG induced/increased enzyme binding and activation, but no microscopic domain separation was observed. The presence of DAG-generated nanodomains, or of DAG-induced lipid packing defects, is proposed instead for this system. In PI/galactosylceramide mixtures, DAG may exert its activation role through the generation of small vesicles, which PI-PLC is known to degrade at higher rates. In general, our results indicate that global measurements obtained using fluorescent probes in vesicle suspensions in a cuvette are not sufficient to elucidate DAG effects that take place at the domain level. The above data reinforce the idea that DAG functions as an important physical agent in regulating membrane and cell properties. © 2015 Biophysical Society.


PubMed | University of the Basque Country and SGiker
Type: Journal Article | Journal: Biophysical journal | Year: 2015

Diacylglycerol (DAG)-induced activation of phosphatidylinositol-phospholipase C (PI-PLC) was studied with vesicles containing PI, either pure or in mixtures with dimyristoyl phosphatidylcholine, distearoyl phosphatidylcholine, sphingomyelin, or galactosylceramide, used as substrates. At 22C, DAG at 33mol % increased PI-PLC activity in all of the mixtures, but not in pure PI bilayers. DAG also caused an overall decrease in diphenylhexatriene fluorescence polarization (decreased molecular order) in all samples, and increased overall enzyme binding. Confocal fluorescence microscopy of giant unilamellar vesicles of all of the compositions under study, with or without DAG, and quantitative evaluation of the phase behavior using Laurdan generalized polarization, and of enzyme binding to the various domains, indicated that DAG activates PI-PLC whenever it can generate fluid domains to which the enzyme can bind with high affinity. In the specific case of PI/dimyristoyl phosphatidylcholine bilayers at 22C, DAG induced/increased enzyme binding and activation, but no microscopic domain separation was observed. The presence of DAG-generated nanodomains, or of DAG-induced lipid packing defects, is proposed instead for this system. In PI/galactosylceramide mixtures, DAG may exert its activation role through the generation of small vesicles, which PI-PLC is known to degrade at higher rates. In general, our results indicate that global measurements obtained using fluorescent probes in vesicle suspensions in a cuvette are not sufficient to elucidate DAG effects that take place at the domain level. The above data reinforce the idea that DAG functions as an important physical agent in regulating membrane and cell properties.

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