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In this work, we test the thermal rupture of a permalloy strip when an electric current is flowing through the strip. For a strip with the top surface exposed to air or covered with a thin insulating layer, we find that the strip gets destroyed at a DC density of only ∼0.6 × 1012 A/m2 and a temperature smaller than 400 K, while it can withstand ∼1.5 × 1012 A/m2 and ∼1200 K if the current is delivered in a sub-μs pulse. If the permalloy strip is covered with a heat dissipation window of Ta2O3/Pt or Ta2O3/Au, so the permalloy can also conduct heat through the top surface, the strip can withstand ∼3.5 × 1012 A/m2 and ∼2000 K. Interestingly, the strips always break in a section not covered by the dissipation window, even if that is not the hottest part of the strip. Therefore, the layers forming the dissipation window help with not only extracting the heat but also delaying the structural damage.

The COVID-19 pandemic has caused a massive disruption in the way traditional higher education institutions deliver their courses. Unlike transitions from face-to-face teaching to blended, online or flipped classroom in the past, changes in emergency remote teaching –a temporary shift of instructional delivery to an alternate remote delivery mode due to crisis circumstances– happen suddenly and in an unplanned way. This study analyzes the move to emergency remote teaching at the School of Telecommunication Engineering (Universidad Politecnica de Madrid), and the impact of organizational aspects related to unplanned change, instruction-related variables –class size, synchronous/asynchronous delivery– and use of digital supporting technologies, on students' academic performance. Using quantitative data of academic records across all (N = 43) courses of a bachelor's degree programme in Telecommunication Engineering and qualitative data from a questionnaire delivered to all (N = 43) course coordinators, the research also compares the academic results of students during the COVID-19 pandemic with those of previous years. The results of this case study show an increase in students' academic performance in emergency remote teaching, and support the idea that organizational factors may contribute to successful implementation of emergency remote teaching; the analysis does not find differences across courses with different class sizes or delivery modes. The study further explores possible explanations for the results of the analysis, considering organizational, individual and instruction-related aspects.

Magnonics rely on the wave nature of the magnetic excitations to process information, an approach that is common to many fields such as photonics, phononics, and plasmonics. Nevertheless, magnons, ...

Surface Acoustic Waves (SAW) are one of the possible solutions to target the challenges faced by modern spintronic devices. The stress carried by the SAW can decrease the current required to achieve magnetic switching or domain wall movement by spin transfer torque. Although the last decade has produced very relevant results in this feld, it is still important to study the efects of a SAW on the basic unit of many spintronic devices, a ferromagnetic nanostrip. In this work, we perform a complete set of measurements and simulations to characterize the magnetization process of a Ni nanostrip under the infuence of a SAW. We fnd that the SAW increases the mobility and the depinning ability of the magnetic domain walls and consequently, promotes a sharper approach to saturation and substantially decreases coercivity. We have also found other two interesting efects. When the SAW has sufcient energy, is able to trigger irreversible transitions even before switching the direction of the external magnetic feld. Additionally, we have found that the magnetization process depends on the direction of the travelling SAW., Projects MAT2017-87072-C4-1-P, MAT2017-87072-C4-4-P and MAT2017- 87072-C4-3-P from the Spanish government and project SA299P18 from the Junta de Castilla y Leon.

[EN] This tutorial explores the problem of Joule heating on metallic micro or nanostrips, still one of the most popular geometries in modern spintronics. Many of the effects that result from the interaction of a spin polarized current and the local magnetization, require of a sizeable current density. This implies, quite often, an unneglectable Joule heating. Despite the few articles devoted to some aspects of Joule heating, there is still disinformation and many misconceptions in this topic, which is key for the correct interpretation of the scientific results. In this tutorial, we highlight the material parameters that are important to keep the temperature of the strip under control and those that give only a marginal advantage. In the vast majority of papers, at least one of these parameters is missing. We also focus on some misconceptions, such as the belief that performing the measurement on a cryostat, rules Joule heating out. In fact, for a fixed current density, measuring in a cryostat decreases the temperature but not enough to justify the use of such a costly measuring set-up. At the practical level, we put forward a 1D model to calculate, in few seconds, if Joule heating is present and if it should be taken into account when interpreting the results. Finally, and importantly, we describe a simple fabrication route to enhance the dissipation of heat in the strip considerably. This fabrication strategy is more effective at keeping the temperature under control than performing the experiment at cryogenic temperatures., Project MAT2017-87072-C4-3-P and MAT2017-87072-C4-1-P from the Spanish government Project No. SA299P18 from Consejería de Educación Junta de Castilla y León

A controlled local enhancement of superconductivity yields unexpected modifications in the vortex dynamics. This local enhancement has been achieved by designing an array of superconducting Nb nanostructures embedded in a V superconducting film. The most remarkable findings are: i) vanishing of the main commensurability effect between the vortex lattice and the array unit cell, ii) hysteretic behavior in the vortex dynamics, iii) broadening of the vortex liquid phase and iv) strong softening of the vortex lattice. These effects can be controlled and they can be quenched by reducing the Nb array superconducting performance applying an in-plane magnetic field. These results can be explained by taking into account the repulsive potential landscape created by the superconducting Nb nanostructures on which vortices move., Comment: 16 pages, 8 figures

[EN]Heating a ferromagnetic material is often perceived as detrimental for most applications. This is indeed the case for modern nano-scaled spintronic devices which are operated solely (at least ideally) by an electric current. Heat is a by-product of the current-driven operation and it deteriorates many functionalities of the device. A large scientific and technological effort is devoted these days to avoid heat in modern magnetic nano devices. Here we show that heat can be used to provide an additional and useful degree of freedom in the control of the local magnetization at the nanoscale. In a ferromagnetic nanowire, temperature is used to induce a magnetic switching through a perfectly deterministic mechanism. The nucleation of the magnetic domain walls that triggers the switching can be achieved at a field considerably smaller than the nucleation field and, importantly, the exact moment of the magnetic switching can be pre-determined with nanosecond precision by controlling the power delivered locally to the switching area. With the help of micromagnetic simulations and a theoretical model, we provide an accurate explanation of how this deterministic thermo-magnetic switching operates. The concepts described in this work may lead to an increased functionality in magnetic nano-devices based on magnetic domain walls., MAT2017-87072-C4-1-P,MAT2017-87072-C4-4-P and MAT2017-87072-C4-3-P from the Spanish government SA299P18 from the Junta de Castilla y Leon POCI-01-0145-FEDER-028676 from Portuguese FCT COMPETE 2020 (FEDER).

6 pags, 4 figs, The precise control and stabilization of magnetic domain walls is key for the development of the next generation magnetic nano-devices. Among the multitude of magnetic configurations of a magnetic domain wall, topologically protected states are of particular interest due to their intrinsic stability. In this work, using XMCD-PEEM, we have observed a topologically protected magnetic domain wall in a ferromagnetic cylindrical nanowire. Its structure is stabilized by periodic sharp alterations of the chemical composition in the nanowire. The large stability of this topologically protected domain wall contrasts with the mobility of other non-protected and non-chiral states also present in the same nanowire. The micromagnetic simulations show the structure and the conditions required to find the topologically protected state. These results are relevant for the design of future spintronic devices such as domain wall based RF oscillators or magnetic memories., This work is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through Projects MAT2014-52477-C5-1-P, 2-P, MAT2015-64110-C2-1-P, 2-P and MAT2017-87072-C4-2-P and by Portuguese FCT and COMPETE 2020, under project POCI-01-0145-FEDER-028676. IMDEA Nanociencia acknowledges support from the Severo Ochoa Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). MPP acknowledges FCT for grant SFRH/BPD/84948/2012. SRG acknowledges MINECO for FPI fellowship.

In this work we study the influence of the thermal contact resistance on the temperature of a typical nanostripe used in current induced magnetic domain wall movement or depinning. The thermal contact resistance arises from an imperfect heat transport across the interface between the metallic ferromagnetic nanostripe and the substrate. We show that this parameter, which is likely non-zero in any experimental device, increases the temperature in the nanostripe considerably. When the current is injected in the nanostripe in nanosecond long pulses, the larger temperature also implies a reduction of the effective current density delivered by the pulse generator. Both the thermal contact resistance and the dynamic response of the pulse generator are usually neglected in theoretical estimations of the influence of spin transfer torque on domain wall displacement and depinning. Here we show that only if the thermal contact resistance and the electric resistivity of the ferromagnetic nanostripe are optimized to the best values reported in the bibliography, the Joule heating may not be so crucial for current densities of the order of 108 A cm−2. Also, the use of physical constrictions (notch) to pin the magnetic domain wall may complicate the interpretation of the results as they always come together with relevant thermal gradients., This work has been partially funded by the Spanish Ministerio de Economía y Competitividad through the projects MAT2014-52477-C5-1-P and MAT2014-52477-C5-3-P and by the Engineering and Physical Sciences Research Council through grant code EPSRC EP/E03389X.

Electron beam lithography is a well-established tool suitable for the modification of substrate surface chemistry. It therefore follows that the deposition and self-assembly of nanoparticles on a surface can be directed using this method. This work explores the effect of electron dose on the electron beam lithographic patterning of self-assembled monolayers (SAMs) on gold surfaces. Electron beam irradiation of the sample induces conversion of the SAM terminal functional aromatic nitro (NO2) moieties to aromatic amino (NH2) moieties. The cationic NH2 functionalised regions direct the site-specific assembly of anionic citrate-passivated gold nanoparticles in aqueous solution at pH 4.5. Control of nanoparticle attachment to the SAM is demonstrated over the exposure range 5000–125,000 uC/cm2. Overexposure led to significant numbers of secondary electrons reaching the surface, causing conversion of functional aromatic moieties outside of the regions irradiated, which reduced feature quality and regional selectivity of adsorption.

In recent years, spin–orbit effects have been widely used to produce and detect spin currents in spintronic devices. The peculiar symmetry of the spin Hall effect allows creation of a spin accumulation at the interface between a metal with strong spin–orbit interaction and a magnetic insulator, which can lead to a net pure spin current flowing from the metal into the insulator. This spin current applies a torque on the magnetization, which can eventually be driven into steady motion. Tailoring this experiment on extended films has proven to be elusive, probably due to mode competition. This requires the reduction of both the thickness and lateral size to reach full damping compensation. Here we show clear evidence of coherent spin–orbit torque-induced auto-oscillation in micron-sized yttrium iron garnet discs of thickness 20 nm. Our results emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current., This research was partially supported by the ANR Grant Trinidad (ASTRID 2012 program). M.C. acknowledges DGA for financial support. V.V.N. acknowledges support from the program CMIRA'Pro of the region Rhône-Alpes. S.O.D. and V.V.N. acknowledge, respectively, support from the Russian programs Megagrant No. 2013-220-04-329 and Competitive Growth of KFU.

Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators., This research was partially supported by the Deutsche Forschungsgemeinschaft, the ANR Grant Trinidad (ASTRID 2012 program), and the program Megagrant No. 14.Z50.31.0025 of the Russian Ministry of Education and Science. M. C. acknowledges DGA for financial support. V. V. N. acknowledges support from the Competitive Growth of KFU.

Tb x Fe 1− x thin films deposited by sputtering on Mo were investigated structurally and magnetically. The microstructure consists of TbFe 2 nanoparticles embedded in an amorphous matrix, and the Tb content can be correlated with an increase in the volume of these nanoparticles. Similar microstructure and behavior were found when TbFe 2 was deposited on glass and on a Pt buffer layer. Nevertheless, thermal treatments promote a different effect, depending on the mechanical stiffness of the buffer layer. The layers deposited on Mo, a rigid material, show crystalline TbFe 2 together with α-Tb phase upon thermal treatment. In contrast, TbFe 2 does not crystallize properly on Pt, a material with a lower stiffness than Mo. Intermediate results were observed on the film deposited on glass. Experimental results show the impact of the buffer stiffness on the crystallization process. Moreover, the formation of α-Tb appears to be fundamental to crystallized TbFe 2 on layers deposited on rigid buffers.

We investigate the symmetry-breaking effects of magnetic nanostructures that present unidirectional (one-fold) magnetic anisotropy. Angular and field dependent transport and magnetic properties have been studied in two different exchange-biased systems, i.e. ferromagnetic (FM)/ antiferromagnetic (AFM) bilayer and spin-valve structures. We experimentally show the direct relationships between the magnetoresistance (MR) response and the magnetization reversal pathways for any field value and direction. We demonstrate that even though the MR signals are related to different transport phenomena, namely anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), chiral asymmetries are found around the magnetization hard-axis direction, in both cases originated from the one-fold symmetry of the interfacial exchange coupling. Our results indicate that the chiral asymmetry of transport and magnetic behaviors are intrinsic of systems with an unidirectional contribution, This work was supported in part by the Spanish MINECO through Project No. MAT2012-39308, FIS2013-40667-P and MAT2014-52477-C5-3-P, and by the Comunidad de Madrid through Project S2013/MIT-2850 (NANOFRONTMAG-CM). P.P. acknowledges support through Marie Curie AMAROUT EU Programme and JCI-2011-09602.

We describe experimental difficulties, and associated artefacts, that arose during the study of thin epitaxial films of the proposed multiferroic materials BiFeO3 and BiMnO3. The problems experienced include large leakage currents and charge injection from Nb-doped SrTiO3 substrates used as bottom electrodes. Charge injection prevents ferroelectric hysteresis loop closure and contributes to the apparent polarization. Leakage currents also contribute to the apparent polarization, and may help explain the large range of polarization values reported in the literature. Convincing reports of a material that is ferromagnetic and ferroelectric at room temperature remain elusive, and indeed we fail to reproduce a previous work concerning Tb-substituted BiFeO3. Our magnetization measurements show this material to be only a weak ferromagnet (0.1 µB/unit cell). Lastly, we show that magnetoelectric measurements are easily corrupted in the presence of large leakage currents.

The temperature in a ferromagnetic nanostripe with a notch subject to Joule heating has been studied in detail. We first performed an experimental real-time calibration of the temperature versus time as a 100 ns current pulse was injected into a Permalloy nanostripe. This calibration was repeated for different pulse amplitudes and stripe dimensions and the set of experimental curves were fitted with a computer simulation using the Fourier thermal conduction equation. The best fit of these experimental curves was obtained by including the temperature-dependent behavior of the electrical resistivity of the Permalloy and of the thermal conductivity of thesubstrate(SiO2). Notably, a nonzero interface thermal resistance between the metallic nanostripe and thesubstrate was also necessary to fit the experimental curves. We found this parameter pivotal to understand ourresults and the results from previous works. The higher current density in the notch, together with the interface thermal resistance, allows a considerable increase of the temperature in the notch, creating a large horizontal thermal gradient. This gradient, together with the high temperature in the notch and the larger current density close to the edges of the notch, can be very influential in experiments studying the current assisted domain wall motion.

The half antivortex, a fundamental topological structure which determines magnetization reversal of submicron magnetic devices with domain walls, has been suggested also to play a crucial role in spin torque induced vortex core reversal in circular disks. Here we report on magnetization reversal in circular disks with nanoholes through consecutive metastable states with half antivortices. In-plane anisotropic magnetoresistance and broadband susceptibility measurements accompanied by micromagnetic simulations reveal that cobalt disks with two and three linearly arranged nanoholes directed at 45 and 135 degrees with respect to the external magnetic field show reproducible step-like changes in the anisotropic magnetoresistance and magnetic permeability due to transitions between different intermediate states mediated by vortices and half antivortices confined to the dot nanoholes and edges, respectively. Our findings are relevant for the development of multi-hole based spintronic and magnetic memory devices.

In this work we have studied with micromagnetic simulations the pinning process of a magnetic domain wall (DW) travelling in a cylindrical magnetic nanowire with a section where the composition has been altered with respect to the rest of the nanowire (chemical constraint). We have studied the depinning process for a non-magnetic, a paramagnetic and a ferromagnetic constraint and we show that the pinning strength in this type of defect can be tailored by a change of composition. The ferromagnetic chemical constraint is the strongest pinning site but it can stop the DW only when there is a significant reduction of the exchange energy and the saturation magnetization with respect to the rest of the wire. Chemical constraints may constitute a promising alternative to geometrical constraints in some devices such as the race-track memory.

We present an experimental study devoted to determine the magnetoresistive signals as imposed by the system magnetic anisotropy and applied current direction in a model ferromagnetic system. By having direct experimental access to the magnetization vector during the reversal (measured through angular- and field-dependent vectorial-resolved magnetization loops), we can predict both longitudinal and transverse magnetoresistive signals, i.e., anisotropic magnetoresistance and planar Hall effect. This has been done by experimentally disclosing the resistance changes occurring during (and simultaneously to) the magnetization reversal processes. © 2014 AIP Publishing LLC., This work was supported in part by the Spanish MINECO through Projects Nos. MAT2012-39308 and MAT2011-25598 and Comunidad de Madrid through the Project No. S2009/MAT-1726. P.P. acknowledges support through the JCI-2011-09602 Contract from the Spanish MINECO and through the Marie Curie AMAROUT EU Programme.

Hybrid magnetic arrays embedded in superconducting films are ideal systems to study the competition between different physical (such as the coherence length) and structural length scales such as are available in artificially produced structures. This interplay leads to oscillation in many magnetically dependent superconducting properties such as the critical currents, resistivity and magnetization. These effects are generally analyzed using two distinct models based on vortex pinning or wire network. In this work, we show that for magnetic dot arrays, as opposed to antidot (i.e. holes) arrays, vortex pinning is the main mechanism for field induced oscillations in resistance R(H), critical current Ic(H), magnetization M(H) and ac-susceptibility χ ac(H) in a broad temperature range. Due to the coherence length divergence at Tc, a crossover to wire network behaviour is experimentally found. While pinning occurs in a wide temperature range up to Tc, wire network behaviour is only present in a very narrow temperature window close to Tc. In this temperature interval, contributions from both mechanisms are operational but can be experimentally distinguished. Fil: Gomez, A. Universidad Complutense de Madrid; España Fil: del Valle, J. Universidad Complutense de Madrid; España Fil: Gonzalez, E. M.. Universidad Complutense de Madrid; España. IMDEA. Madrid; España Fil: Chiliotte, Claudio Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Carreira, Santiago José. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Bekeris, Victoria Isabel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Prieto, J. L.. Universidad Politécnica de Madrid; España Fil: Schuller, Ivan K.. University of California at San Diego; Estados Unidos Fil: Vicent, J. L.. IMDEA. Madrid; España. Universidad Complutense de Madrid; España

Some important improvements in magnetostrictive piezoelectric sensors have been obtained by applying an alternating current to the ferromagnetic amorphous ribbon. First, we present a way to minimize the hysteresis in these devices using a demagnetizing current through the magnetic sample. Second, the current, at a frequency half that of the longitudinal piezoelectric resonance, is used to induce size changes in the high-magnetostriction amorphous ribbon, and these changes, which depend on the external magnetic field, can be read by the piezoelectric support. Then, with this configuration, it is not necessary to have a coil for the detection of a magnetic field.

Repeatable magnetization reversal under purely electrical control remains the outstanding goal in magnetoelectrics. Here we use magnetic force microscopy to study a commercially manufactured multilayer capacitor that displays strain-mediated coupling between magnetostrictive Ni electrodes and piezoelectric BaTiO(3)-based dielectric layers. In an electrode exposed by polishing approximately normal to the layers, we find a perpendicularly magnetized feature that exhibits non-volatile electrically driven repeatable magnetization reversal with no applied magnetic field. Using micromagnetic modelling, we interpret this nominally full magnetization reversal in terms of a dynamic precession that is triggered by strain from voltage-driven ferroelectric switching that is fast and reversible. The anisotropy field responsible for the perpendicular magnetization is reversed by the electrically driven magnetic switching, which is, therefore, repeatable. Our demonstration of non-volatile magnetic switching via volatile ferroelectric switching may inspire the design of fatigue-free devices for electric-write magnetic-read data storage.

We discuss the magnetization processes in sensors based on the superposition of a magneto‐ restrictive amorphous ribbon over a piezoelectric plate. These devices show an unusual behavior of the null condition in the response curves, which we have related theoretically and experimentally to the coercive force of the magnetic sample and to changes in the magnetic domain pattern for frequencies near the longitudinal piezoelectric resonance frequency.

A generalized procedure for the in situ application of magnetic fields by means of the excitation of the objective lens for magnetic imaging experiments in Lorentz microscopy and electron holography is quantitatively described. A protocol for applying magnetic fields with arbitrary in-plane magnitude and orientation is presented, and a freeware script for Digital Micrograph¿ is provided to assist the operation of the microscope. Moreover, a method to accurately reconstruct hysteresis loops is detailed. We show that the out-of-plane component of the magnetic field cannot be always neglected when performing quantitative measurements of the local magnetization. Several examples are shown to demonstrate the accuracy and functionality of the methods., This work was supported by the Spanish Ministry of Economy and Innovation (MINECO) through Projects MAT2009-08771, MAT2011-28532-C03-02, MAT2011-28532-C03-03 and MAT2011-27553-C02 including FEDER funding, by the Aragón Regional Government through Projects E26 and CTPP4/11, and the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative, Reference 312483-ESTEEM2.

We examine the vortex lattice (VL) dynamics in superconducting Nb films containing square and rectangular arrays of Ni nanodots, using ac susceptibility techniques. A remarkable robust feature is the increase in pinning that occurs for magnetic fields that create integer n or half integer flux lines per pinning cell. This phenomenology has been reported in transport experiments performed very close to the sample critical temperature TC. In our contactless experiments we determined vortex mobility and pinning properties in an extended temperature range 0.65

We explore the influence of Fe content on the interfacial magnetic properties of Ni${}_{1\ensuremath{-}x}$Fe${}_{x}$(50 \AA{})/Fe ($t$ \AA{})/Gd(50 \AA{})/Fe ($t$ \AA{})/Ni${}_{1\ensuremath{-}x}$Fe${}_{x}$(50 \AA{}) ($x$ $=$ 0.2 and 0.6, and $t$ $=$ 0 and 10 \AA{}) multilayers by means of element-specific x-ray magnetic circular dichroism measurements at Gd M${}_{5}$ and (Ni, Fe) L${}_{2,3}$ absorption edges, superconducting quantum interference device magnetometry, and specular reflectivity measurements. Increasing Fe content in the Ni-Fe layer enhances the Gd ordering temperature in the interfacial regions. Addition of a 1-nm Fe spacer results in the largest enhancement in Gd ordering temperature in both interior and interfacial Gd regions, even for high Ni content in the Ni-Fe layer. This indicates that the Fe spacers act as effective barriers (albeit imperfect) in reducing Gd-Ni contact interactions responsible for limiting the interfacial Gd magnetic ordering temperature to values larger than bulk Gd, but significantly lower than observed at Fe/Gd interfaces.

Perna, P. et al., The simultaneous determination of magnetoresistance and vectorial-resolved magnetization hysteresis curves in a spin valve structure reveals distinct magnetoresistive features for different magnetic field orientations, which are directly related to the magnetization reversal processes. Measurements performed in the whole angular range demonstrate that the magnetoresistive response originates from the intrinsic anisotropic angular dependence of the magnetization orientation between the two ferromagnetic layers. This also provides direct proof that the spin-dependent scattering in the bulk of the magnetic layers is at the origin of the magnetoresistive signal. © 2012 American Physical Society., This work was supported in part by the Spanish MICINN through Project No. CSD2007-00010 and FIS 2010-18847 and by the Comunidad de Madrid through Project No. S2009/MAT-1726. P.P. acknowledges support through the Marie Curie AMAROUT EU action and the Spanish MICINN “Juan de la Cierva” contract. A.B. acknowledges support through the “Ramón y Cajal” contract from the Spanish MICINN.

The process of injection of a magnetic domain wall (DW) by means of a 25--100 ns current pulse flowing through an adjacent conductive track has been studied in detail. We find that the probability of creating a DW through this method is 100% for a wide range of amplitudes of the current pulse and of the external magnetic field, including zero external magnetic field. Micromagnetic simulations show that the DW is created in the first nanosecond of the pulse, and its movement is strongly influenced by the induced Oersted field, which can reach considerable values, especially in the perpendicular-to-plane direction. The edge roughness and temperature play also a crucial role in determining the type of DW that travels through the wire. Experimentally we show that a map of the probability of injection of a DW by a current pulse can be a very powerful method to check the structural quality of the nanostripe, which has very important practical consequences for research in this area.

5 páginas, 6 figuras.-- PACS number(s): 75.70.−i, 75.47.De, 75.60.Ej, The exchange interaction of Gd adjacent to Fe has been characterized by transport measurements on a double spin valve with a Fe/Gd/Fe trilayer as the middle layer. Our measurements show that the ferromagnetism of the Gd is enhanced by the presence of the Fe, and it remains ferromagnetic over its Curie temperature up to a thickness no smaller than 1 nm adjacent to the Fe. This thickness is more than double what has been reported before. Additionally, the saturation magnetization of the thin Gd layer sandwiched in Fe was found to be half of its bulk value. This reduced magnetization does not seem to be related to the proximity of Fe but rather to the incomplete saturation of Gd even for very high fields., This work was partially supported by Project Nos. MAT2008-02770/NAN and MAT2009-08771 from the SpanishMinisterio deCiencia e Innovaci´on. M. Romerawas funded through the FPU Fellowship No. AP2007-00464.

Nanofabrication has allowed the development of new concepts such as magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls on magnetic nanostripes. One of the issues that has to be solved before devices can meet the market demands is the stochastic behaviour of the domain wall movement in magnetic nanostripes. Here we show that the stochastic nature of the domain wall motion in permalloy nanostripes can be suppressed at very low fields (0.6-2.7 Oe). We also find different field regimes for this stochastic motion that match well with the domain wall propagation modes. The highest pinning probability is found around the precessional mode and, interestingly, it does not depend on the external field in this regime. These results constitute an experimental evidence of the intrinsic nature of the stochastic pinning of domain walls in soft magnetic nanostripes. © 2011 Macmillan Publishers Limited. All rights reserved., This work was funded by MAT2008-02770/NAN and MAT2009-08771 from the Spanish Ministerio de Ciencia e Innovación.

The 2008 optical transient in NGC 300 is one of a growing class of intermediate-luminosity transients that brighten several orders of magnitude from a previously optically obscured state. The origin of their eruptions is not understood. Our multi-wavelength photometry and spectroscopy from maximum light to more than a year later provide a record of its post-eruption behavior. We describe its changing spectral-energy distribution, the evolution of its absorption- and emission line-spectrum, the development ofa bipolar outflow, and the rapid transition from a dense wind to an optically thin ionized wind. In addition to strong, narrow hydrogen lines, the F-type absorption-line spectrum of the transient is characterized by strong Ca II and [Ca II] emission. The very broad wings of the Ca II triplet and the asymmetric [Ca II] emission lines are due to strong Thomson scattering in the expanding ejecta. Post-maximum, the hydrogen and Ca II lines developed double-peaked emission profiles that we attribute to a bipolar outflow. Between approximately 60 and 100 days after maximum, the F-type absorption spectrum, formed in its dense wind, weakened and the wind became transparent to ionizing radiation. We discuss the probable evolutionary state of the transient and similar objects such as SN 2008S, and conclude thatthey were most likely post-red supergiants or post-AGB stars on a blue loop to warmer temperatures when the eruption occurred. These objects are not LBVs., Comment: Submitted to ApJ

The effects of patterning highly anisotropic repeating structures in soft magnetic thin films have been examined. Arrays of wires with equal mark/space ratios were patterned in resist using optical lithography. 100 nm thick Ni/sub 80/Fe/sub 15/Mo/sub 5/ films were partially or completely etched using broad beam ion milling to assess the dependence of magnetic properties on the degree of interconnection between the wires. These structures show a progressive increase in coercivity and a transition between single and two-stage switching with increasing milling depth. A similar nanopatterning technique has been applied to unpinned (Ni/sub 80/Fe/sub 20//Cu/Ni/sub 80/Fe/sub 20/) spin valve structures in order to enhance the coercivity of one of the ferromagnetic layers; the increased coercivity induced by patterning changes the natural similarity of the magnetic layers and the completed structure exhibits a small spin valve response.

This study explores experimentally the stochastic nature of the domain wall depinning in permalloy nanowires using notches of various shapes and depths. The presence of the domain wall in the notch is detected through its anisotropic magnetoresistance (AMR), which is measured with high precision in order to detect even small changes in the domain wall profile. These measurements showed that variations in the depinning field are related with changes, sometimes very small, in the AMR profile, which indicates that small changes in the pinned domain wall profile can affect largely the depinning process. As these small changes are many times unpredictable and uncontrollable, the stochastic nature of the depinning could have negative consequences for practical applications based on permalloy nanowires.

A new working configuration for magnetostrictive-piezoelectric magnetic sensors is presented. In this configuration, the excitation is caused using an electrical current flowing through the ferromagnetic sample and the induced signal is sensed in the piezoelectric support as an electrical voltage. This new idea allows a magnetic field detection without any coil and opens a possibility for a future miniaturisation of the sensor.

In thin-film ${\text{La}}_{0.6}{\text{Ca}}_{0.4}{\text{MnO}}_{3}$, conducting-tip and magnetic force microscopy reveal a pattern of nanoscale phase separation that is reproducible across cooling runs. This pattern represents the intersection of buried three-dimensional filamentary ferromagnetic metallic pathways with the sample surface. As an interlayer in current-perpendicular-to-the-plane trilayer devices, this phase-separated material magnetically decouples ferromagnetic metallic ${\text{La}}_{0.7}{\text{Ca}}_{0.3}{\text{MnO}}_{3}$ electrodes which switch sharply. This yields sharp two-state low-field magnetoresistance that is also reproducible across cooling runs. The reproducibility and the magnitude of the resistance jump are linked to highly resistive $(\ensuremath{\sim}{10}^{\ensuremath{-}12}\text{ }\ensuremath{\Omega}\text{ }{\text{m}}^{2})$ constrained domain walls in the pathways of the phase-separated interlayer. Phase separation is normally associated with high-field colossal magnetoresistance and, therefore, its exploitation here to produce low-field effects is unusual.

Magnetoelectric coupling between magnetic and electrical properties presents valuable degrees of freedom for applications. The two most promising scenarios are magnetic-field sensors that could replace low-temperature superconducting quantum interference devices, and electric-write magnetic-read memory devices that combine the best of ferroelectric and magnetic random-access memory. The former scenario requires magnetically induced continuous and reversible changes in electrical polarization. These are commonly observed, but the coupling constants thus obtained are invalid for data-storage applications, where the more difficult to achieve and rarely studied magnetic response to an electric field is required. Here, we demonstrate electrically induced giant, sharp and persistent magnetic changes (up to 2.3 x 10(-7) s m(-1)) at a single epitaxial interface in ferromagnetic 40 nm La(0.67)Sr(0.33)MnO(3) films on 0.5 mm ferroelectric BaTiO(3) substrates. X-ray diffraction confirms strain coupling via ferroelastic non-180( composite function) BaTiO(3) domains. Our findings are valid over a wide range of temperatures including room temperature, and should inspire further study with single epitaxial interfaces.

We have performed current perpendicular-to-plane measurements in Gd-transition metal multilayers and amorphous ${\mathrm{Co}}_{x}{\mathrm{Gd}}_{1\ensuremath{-}x}∕{\mathrm{Co}}_{y}{\mathrm{Gd}}_{1\ensuremath{-}y}$ bilayers. Both systems create in-plane exchange spring domain walls (SWs) whose width can be controlled by an external magnetic field. The results can be explained fully by Lorentz magnetoresistance (MR) plus the effect of the interface. They show no intrinsic scattering from the SWs, suggesting that the ``mistracking'' of the spin to the local magnetization is not the main cause of MR of domain walls but the change of spin populations across a thin barrier as in GMR structures.

The possibility of performing spintronics at the molecular level may be realized in devices that combine fully spin polarized oxides such as manganites with carbon nanotubes. However, it is not clear whether electrical transport between such different material systems is viable. Here we show that the room temperature conductance of manganite-nanotube-manganite devices is only half the value recorded in similar palladium-nanotube-palladium devices. Interestingly, the former shows a pseudogap in the conductivity below the relatively high temperature of 200 K. Our results suggest the possibility of new spintronics heterostructures that exploit fully spin polarized sources and drains.

Estimating time since death is especially difficult in the examination of poorly preserved cadavers and depends on the experience of the examiner and comparison with previously documented cases showing similar characteristics. The present study reports on information obtained over the past ten years through the work of the Laboratorio de Antropología y Odontología Forense (LAF) of the Instituto Anatómico Forense de Madrid, Spain, in particular evaluating how the type of fracture influences postmortem change. From the original 225 forensic cases examined between 1992 and 2002 in the LAF, a sample of 29 cases were selected from various regions of the Spanish mainland. A data collection protocol was established to reflect factors which the existing specialized literature, documenting the relation existing in the sample analyzed between time since death and the extent of postmortem change, which in the environments examined are distributed into the following phases: Phase 1 (putrefaction): one week to one month on the surface and two months in water. Phase 2 (initial skeletonization): two months on the surface and five to six months in water. Phase 3 (advanced skeltonization): six months to 1.5 years on the surface and 2.5 years buried. Phase 4 (complete skeletonization): about one year on the surface and three years buried. This paper also provide useful information on the impact of carrion insect activity, location, climate, seasonality, and predator.

The transport properties of sharp antiferromagnetic boundaries between Gd and Fe have been studied. The measurements were carried out with the current perpendicular to the plane at 20 K and up to 8 T in multilayer Gd/Fe of different thicknesses. We have extended the Valet and Fert model for giant magnetoresistive multilayers to explain the results in terms of spin-dependent scattering at the interface that changes its magnitude when the external field decreases the angle of the interface.

We show that a thin Gd layer inserted between two thicker layers of permalloy contains an in-plane domain wall whose width can be controlled by varying the thickness of the Gd layer. The magnetoresistance of this structure has been measured with the current perpendicular to the plane, thus eliminating spurious contributions which have complicated previous measurements. This is the first measurement to show unambiguously that the domain wall contributes an additional resistance whose magnitude is in good agreement with theory.

We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T>0.70 T C . The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the J C (T) behavior. Moreover, the temperature dependence of the pinning force F P (T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex-vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena. Fil: Moreno Jiménez, Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Chiliotte, Claudio Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Pasquini, Gabriela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Bekeris, Victoria Isabel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: J. del Valle. Universidad Complutense de Madrid; España Fil: E. M. González. Universidad Complutense de Madrid; España Fil: J. L. Prieto. Universidad Politécnica de Madrid; España Fil: J. L. Vincent. Universidad Complutense de Madrid; España

This work explores the conditions that allow the injection and pinning of different magnetic domain walls (DWs) in Permalloy nanostripes with notches of different shapes. The injection is done under a constant external field by applying a 10 ns current pulse through an adjacent current line. The type of DW is identified by its anisotropic magnetoresistance (AMR). We find that, while a quasi-static pinning (nucleating at zero field and propagating the DW to the notch by slowly increasing the external field) would allow to distinguish different types of DWs pinned at the notch, a dynamic pinning (nucleating, propagating, and pinning the DW under a constant non-zero magnetic field) makes the discrimination of different DWs very difficult. Micromagnetic simulations indicate that the AMR of the different types of DWs become quite similar to each other as the injection field increases. This might explain why at large injection fields, usually only one or two values of resistance are detected, depending on the shape of the notch. Therefore, caution should be taken when establishing a one-to-one relationship between a type of DW and a value of resistance, especially if the injection is done under a non-zero external magnetic field.

Resumen basado en el de la publicación El currículo en dos disciplinas de la Historia de la Ciencia en Secundaria ha sido elaborado como parte de las actividades de una experiencia singular del Seminario Orotava de Historia de la ciencia. La filosofía del modelo considera la ciencia como una parte esencial de la cultura y la interdisciplinariedad como el método más adecuado de enseñanza y aprendizaje significativo. Cataluña ESP