Magnetoelasticity and magnetoresistance in Cu-Al-Mn shape-memory alloys

We study the effect of a magnetic field on the martensitic transition of a Cu-Al-Mn shape-memory alloy. The martensitic transition has been studied through resistance measurements under applied magnetic fields ranging from 0 to 50 kOe. Negative magnetoresistance showing an almost linear dependence with the square of the magnetization has been observed. This magnetoresistive effect is associated with the existence of small ferromagnetic Mn-clusters. Its strength and thermal dependence is different in both phases. The martensitic transition temperature is slightly increased and its spread in temperature significantly reduced upon increasing the field. These results show the existence of magnetoelastic coupling, which favors the nucleation of those martensitic variants with the easy magnetization axis aligned with the field.

Magnetoelasticity and magnetoresistance in Cu-Al-Mn shape-memory alloys

We study the effect of a magnetic field on the martensitic transition of a Cu-Al-Mn shape-memory alloy. The martensitic transition has been studied through resistance measurements under applied magnetic fields ranging from 0 to 50 kOe. Negative magnetoresistance showing an almost linear dependence with the square of the magnetization has been observed. This magnetoresistive effect is associated with the existence of small ferromagnetic Mn-clusters. Its strength and thermal dependence is different in both phases. The martensitic transition temperature is slightly increased and its spread in temperature significantly reduced upon increasing the field. These results show the existence of magnetoelastic coupling, which favors the nucleation of those martensitic variants with the easy magnetization axis aligned with the field.

Static structure and dynamics of the liquid Li-Na and Li-Mg alloys

We present calculations for the static structure and ordering properties of two lithium-based s-p bonded liquid alloys, Li-Na and Li-Mg. Our theoretical approach is based on the neutral pseudoatom method to derive the interatomic pair potentials, and on the modified-hypernetted-chain theory of liquids to obtain the liquid static structure, leading to a whole combination that is free of adjustable parameters. The study is complemented by performing molecular dynamics simulations which, besides checking the theoretical static structural results, also allow a calculation of some dynamical properties. The obtained results are compared with the available experimental data.

Ni-Mn-Ga thin films produced by pulsed laser deposition

Polycrystalline Ni-Mn-Ga thin films have been deposited by the pulsed laser deposition (PLD) technique, using slices of a Ni-Mn-Ga single crystal as targets and onto Si (100) substrates at temperatures ranging from 673 K up to 973 K. Off-stoichiometry thin films were deposited at a base pressure of 1×10-6-Torr or in a 5 mTorr Ar atmosphere. Samples deposited in vacuum and temperatures above 823 K are magnetic at room temperature and show the austenitic {220} reflection in their x-ray diffraction patterns. The temperature dependences of both electrical resistance and magnetic susceptibility suggest that these samples exhibit a structural martensitic transition at around 260 K. The magnetoresistance ratio at low temperature can be as high as 1.3%, suggesting the existence of a granular structure in the films

Magnetic field induced entropy change and magnetoelasticity in Ni-Mn-Ga alloys

The magnetocaloric effect that originates from the martensitic transition in the ferromagnetic Ni-Mn-Gashape-memory alloy is studied. We show that this effect is controlled by the magnetostructural coupling at boththe martensitic variant and magnetic domain length scales. A large entropy change induced by moderatemagnetic fields is obtained for alloys in which the magnetic moment of the two structural phases is not verydifferent. We also show that this entropy change is not associated with the entropy difference between themartensitic and the parent phase arising from the change in the crystallographic structure which has beenfound to be independent of the magnetic field within this range of fields.

A first-principles analysis of the magnetism of CuII polynuclear coordination complexes: the case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5H2O

The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5 H2Ocrystal - using fractional coordinates determined at room-temperature ¿ has beenanalysed in detail. This analysis has been carried out by extending our first principlesbottom-up theoretical approach, which was initially designed to study through-spacemagnetic interactions, to handle through-bond magnetic interactions. The only input datarequired by this approach are the values of the computed JAB exchange parameters for allthe unique pairs of spin-containing centres. The results allow the magnetic structure ofthe crystal, which presents two types of isolated tetranuclear CuII clusters, to be definedin quantitative terms. Each of these clusters presents ferro and antiferromagneticinteractions, the former being stronger, although outnumbered by the latter. Thecomputed magnetic susceptibility curve shows the same qualitative features as theexperimental data. However, there are small differences that are presumed to beassociated with the use of room-temperature crystal coordinates.

Ab initio study of MF2 (M=Mn, Fe, Co, Ni) rutile-type compounds using the periodic unrestricted Hartree-Fock approach

The ab initio periodic unrestricted Hartree-Fock method has been applied in the investigation of the ground-state structural, electronic, and magnetic properties of the rutile-type compounds MF2 (M=Mn, Fe, Co, and Ni). All electron Gaussian basis sets have been used. The systems turn out to be large band-gap antiferromagnetic insulators; the optimized geometrical parameters are in good agreement with experiment. The calculated most stable electronic state shows an antiferromagnetic order in agreement with that resulting from neutron scattering experiments. The magnetic coupling constants between nearest-neighbor magnetic ions along the [001], [111], and [100] (or [010]) directions have been calculated using several supercells. The resulting ab initio magnetic coupling constants are reasonably satisfactory when compared with available experimental data. The importance of the Jahn-Teller effect in FeF2 and CoF2 is also discussed.

A first-principles analysis of the magnetism of CuII polynuclear coordination complexes: the case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5H2O

The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5 H2Ocrystal - using fractional coordinates determined at room-temperature ¿ has beenanalysed in detail. This analysis has been carried out by extending our first principlesbottom-up theoretical approach, which was initially designed to study through-spacemagnetic interactions, to handle through-bond magnetic interactions. The only input datarequired by this approach are the values of the computed JAB exchange parameters for allthe unique pairs of spin-containing centres. The results allow the magnetic structure ofthe crystal, which presents two types of isolated tetranuclear CuII clusters, to be definedin quantitative terms. Each of these clusters presents ferro and antiferromagneticinteractions, the former being stronger, although outnumbered by the latter. Thecomputed magnetic susceptibility curve shows the same qualitative features as theexperimental data. However, there are small differences that are presumed to beassociated with the use of room-temperature crystal coordinates.

Memòria del projecte: Trajectòries d'èxit de joves immigrants a l'ensenyament superior i al món professional

[cat] L'educació dels immigrants és un tema prioritari a les agendes polítiques de molts països de la OCDE. En molts casos, els governs s'han preocupat especialment de la seva integració al món del treball però creix l'interès en els seus resultats al sistema educatiu i en la revisió de les polítiques adreçades a respondre a les seves necessitats educatives i formatives. La majoria d'aquests estudis es situen a l'esfera de l'educació infantil, primària, secundaria i formació professional, per això resulta pràcticament impossible trobar informes que analitzin el baix percentatge d'accés d'estudiants immigrants extracomunitaris a la universitat (al voltant de 3,3% en el cas de Catalunya); que contribueixin a entendre els factors que configuren les trajectòries d'èxit escolar i d'integració laboral dels estudiants immigrants que accedeixen i completen els estudis universitaris; que puguin donar pautes per desenvolupar polítiques educatives que millorin els resultats d'aprenentatge dels estudiants immigrants; i que puguin servir com a mirall i incentiu per a altres persones immigrants i, perquè no, també del país. Aquest projecte ha estudiat el conjunt d'elements que condicionen l'accés dels joves immigrants als estudis universitaris, i a l'estatus laboral que els hi hauria de possibilitar la seva formació universitària.L'estudi ha consistit en una metaanàlisi dels documents existents sobre el tema i en la realització de 8 narratives biogràfiques; quatre de persones cursant diferents estudis a les universitats catalanes i quatre que ja s'han incorporat al món del professional. Aquestes narratives venen acompanyades de 8 vídeos que exploren noves maneres de visibilització d'aquesta població i es transformen en una pràctica d'autoria. Aquest material visual pot servir com a recurs educatiu, en la mida que pugui ser un mirall i un incentiu per a altres persones immigrants i del país.Finalment, presenta un seguit de recomanacions per als responsables de les polítiques i dels centres educatius.

Internet i el món Universitari

Internet va néixer a mitja dècada deis anys setanta com a resultat de l'interès del Departament de Defensa deis Estats Units per interconnectar diverses xarxes per mitja de satèl·lit i radio. Es buscava mantenir una xarxa d'informació sobre investigació militar. La xarxa va ser connectada inicialment a quatre institucions acadèmiques' amb el propòsit de facilitar els treballs de recerca que estaven realitzant per al Departament de Defensa. De mica en mica aquesta xarxa es va estendre a d'altres centres universitaris i va esdevenir un sistema de comunicació i d'intercanvi d'informació entre investigadors.

Presentació Monografia: Educació i cooperació internacional en el marc de les desigualtats

La idea de cooperar o de fer cooperació internacional s'ha anat incorporant a les nostres vides -també en la vida acadèmica- en els darrers deu anys, sense que moltes vegades s'hagi aprofundit suficientment en què vol dir, no només etimol6gicament. En aquests moments, en els quals la situació en el món i les complexes relacions internacionals han experimentat canvis importants, s'imposa que ens aturem a pensar una mica sobre el perquè, el com, on i amb qui fem la cooperació internacional. Sobre el paper de l'educació en aquests nous contextos i, més en concret, en el que les universitats fan o poden fer en el que anomenem cooperació per al desenvolupament.