Evidence of the spin Seebeck effect in Ni-Zn ferrites polycrystalline slabs

We report on the observation of the spin Seebeck effect in Ni-Zn ferrites slabs with different Zn concentration. All samples have a spinel structure confirmed by XRD and TEM. We fully characterize the magnetic properties by VSM and Mössbauer spectroscopy. Samples exhibit a nonmonotonic magnetization behavior depending on the structural inversion parameter, however we found a spin Seebeck response voltage of about 25.5 nV/K independent of the magnetization and the inversion degree

Novel Ir1–xCoxO2 thin films: Growth and characterization

Ir1–xCoxO2 thin films have been prepared by reactive co–sputtering deposition at room temperature. Composition, structure, electronic properties and electric and magnetic behavior have been analyzed by different techniques including XRR, XRD, TEM microscopy, SQUID magnetometry, electrical resistivity and XAS spectroscopy. After annealing, an Ir1–xCoxO2 substitutional solid solution phase with rutile crystal structure was achieved for a wide Co-doping range 0 ≤ x ≤ 0.6. Starkly departing from the highly insulating behavior of CoO and Co3O4, the electrical resistivity at room temperature of our films is only slightly higher than that of IrO2. Likewise, our work shows that the magnetic response of the doped films is very similar to that of the paramagnetic parent IrO2. Neither ferromagnetism nor enhanced paramagnetism is observed. XAS spectra indicate a Co3+ oxidation state and, correspondingly, an oxidation state of ∼5+ for Ir ions in the polycrystalline Ir0.6Co0.4O2 film. By application of sum rules, a 13 % increase in the spin–orbit coupling is found despite the lattice shrinkage causes a detrimental bandwidth broadening

Spatio-temporal behaviour of atomic-scale tribo-ceramic films in adaptive surface engineered nano-materials

Atomic-scale, tribo-ceramic films associated with dissipative structures formation are discovered under extreme frictional conditions which trigger self-organization. For the first time, we present an actual image of meta-stable protective tribo-ceramics within thicknesses of a few atomic layers. A mullite and sapphire structure predominates in these phases. They act as thermal barriers with an amazing energy soaking/ dissipating capacity. Less protective tribo-films cannot sustain in these severe conditions and rapidly wear out. Therefore, a functional hierarchy is established. The created tribo-films act in synergy, striving to better adapt themselves to external stimuli. Under a highly complex structure and non-equilibrium state, the upcoming generation of adaptive surface engineered nano-multilayer materials behaves like intelligent systems - capable of generating, with unprecedented efficiency, the necessary tribo-films to endure an increasingly severe environment

Temperature dependence of the spin Seebeck effect in [Fe3O4/Pt]n multilayers

We report temperature dependent measurements of the spin Seebeck effect (SSE) in multilayers formed by repeated growth of a Fe3O4/Pt bilayer junction. The magnitude of the observed enhancement of the SSE, relative to the SSE in the single bilayer, shows a monotonic increase with decreasing the temperature. This result can be understood by an increase of the characteristic length for spin current transport in the system, in qualitative agreement with the recently observed increase in the magnon diffusion length in Fe3O4 at lower temperatures. Our result suggests that the thermoelectric performance of the SSE in multilayer structures can be further improved by careful choice of materials with suitable spin transport properties

Large memcapacitance and memristance at Nb:SrTiO3/La0.5Sr0.5Mn0.5Co0.5O3-d topotactic redox interface

The possibility to develop neuromorphic computing devices able to mimic the extraordinary data processing capabilities of biological systems spurs the research on memristive systems. Memristors with additional functionalities such as robust memcapacitance can outperform standard devices in key aspects such as power consumption or miniaturization possibilities. In this work, we demonstrate a large memcapacitive response of a perovskite memristive interface, using the topotactic redox ability of La0.5Sr0.5Mn0.5Co0.5O3-d (LSMCO, 0 = d = 0.62). We demonstrate that the multi-mem behavior originates at the switchable n-p diode formed at the Nb:SrTiO3/LSMCO interface. We found for our Nb:SrTiO3/LSMCO/Pt devices a memcapacitive effect CHIGH/CLOW ~100 at 150 kHz. The proof-of-concept interface reported here opens a promising venue to use topotactic redox materials for disruptive nanoelectronics, with straightforward applications in neuromorphic computing technology

Spin Seebeck effect in insulating epitaxial ¿-Fe2O3 thin films

We report the fabrication of high crystal quality epitaxial thin films of maghemite (¿-Fe2O3), a classic ferrimagnetic insulating iron oxide. Spin Seebeck effect (SSE) measurements in ¿-Fe2O3/Pt bilayers as a function of sample preparation conditions and temperature yield a SSE coefficient of 0.5(1) µV/K at room temperature. Dependence on temperature allows us to estimate the magnon diffusion length in maghemite to be in the range of tens of nanometers, in good agreement with that of conducting iron oxide magnetite (Fe3O4), establishing the relevance of spin currents of magnonic origin in magnetic iron oxides

Propiedades físicas y cristalinas del Cd1-x Znx Te (0 <= x <= 1)

El Cd1-xZnxTe (0 <= x <= 1) y el ZnTe son semiconductores de la familia II-VI, que se usan en forma monocristalina porque así poseen mejores propiedades estructurales y eléctricas. El CZT y el ZnTe deben poseer alta calidad cristalina y eléctrica para ser usados, el primero en detectores de rayos X y ?, y como sustratos ordenadores de películas epitaxiales aptas para la detección de la radiación IR y el segundo para la fabricación de diodos láser y emisores de luz de alta intensidad, ambos casos en el verde. En este trabajo el CZT se sintetizó por el método de Bridgman, bajo un gradiente de temperatura de 10ºC/cm a velocidades de 1, 66 mm/h y 3, 22 mm/h para diferentes concentraciones de Zn. Por otro lado, el ZnTe se sintetizó por transporte físico en fase vapor bajo un gradiente de temperatura de 6ºC/cm a una velocidad de 6mm/día. Por medio de revelado químico y microscopía electrónica de transmisión convencional TEM y de alta resolución (HRTEM) se estudió la calidad cristalina de ambos materiales. Se observó que los lingotes de CZT tenían una densidad de dislocaciones promedio similar en todos los lingotes crecidos en ambas velocidades y para todas las concentraciones mientras que el ZnTe mostró una menor densidad de dislocaciones. Las micrografías de TEM mostraron en todos estos materiales un orden estructural importante. Estas características indicaron que la calidad cristalina del CZT y del ZnTe era adecuada para fabricar dispositivos optoelectrónicos. También se midió la Conductividad Eléctrica, Difusividad Térmica, Calor Específico y Coeficiente Seebeck en función de la temperatura en estos materiales. Se analizó la influencia de las propiedades estructurales en sus propiedades físicas con el objeto de determinar la relación con los defectos cristalinos observados. Cd1-xZnxTe (0 = x = 1) and ZnTe are II-VI semiconductors, which are used in single crystalline structure to improve their crystalline and electrical properties. The CZT and ZnTe must possess high crystalline and electrical quality to be used, the first in x or ¿-ray detectors, and as substrates for suitable epitaxial films for detecting IR radiation and the second for the manufacture of laser diodes and high intensity light emitters, both cases in the green wavelengths. In this work CZT was synthesized by the Bridgman method employing a temperature gradient of 10ºC/cm at speeds of 1.66 mm/h and 3.22 mm/h for different Zn concentrations. Meanwhile ZnTe was synthesized by physical vapor transport employing a temperature gradient of 6ºC/cm at a speed of 6 mm/day. Chemical etching and low and high transmission electron microscopy (LRTEM and HRTEM) were employed to determine the crystalline quality of all materials. It was observed that CZT ingots had an average dislocations density similar in all ingots grown in both speeds and all concentrations while the ZnTe showed a lower dislocation density. HRTEM micrographs showed in all semiconductors an important structural order. These characteristics showed that the crystalline quality of CZT and ZnTe was suitable for manufacturing optoelectronic devices. Furthermore, Electrical Conductivity, Thermal Diffusivity, Specific Heat and Seebeck Coefficient were measured as temperature function in all these materials. The influence of structural properties in physical properties was analyzed in order to determine the relationship with the observed crystal defects

Adjusting the Neel relaxation time of Fe3O4/ZnxCo1-xFe2O4 core/shell nanoparticles for optimal heat generation in magnetic hyperthermia

In this work it is shown a precise way to optimize the heat generation in high viscosity magnetic colloids, by adjusting the Neel relaxation time in core/shell bimagnetic nanoparticles, for magnetic fluid hyperthermia (MFH) applications. To pursue this goal, Fe3O4/ZnxCo1-xFe2O4 core/shell nanoparticles were synthesized with 8.5 nm mean core diameter, encapsulated in a shell of similar to 1.1 nm of thickness, where the Zn atomic ratio (Zn/(Zn + Co) at%) changes from 33 to 68 at%. The magnetic measurements are consistent with a rigid interface coupling between the core and shell phases, where the effective magnetic anisotropy systematically decreases when the Zn concentration increases, without a significant change of the saturation magnetization. Experiments of MFH of 0.1 wt% of these particles dispersed in water, in Dulbecco modified Eagles minimal essential medium, and a high viscosity butter oil, result in a large specific loss power (SLP), up to 150 W g(-1), when the experiments are performed at 571 kHz and 200 Oe. The SLP was optimized adjusting the shell composition, showing a maximum for intermediate Zn concentration. This study shows a way to maximize the heat generation in viscous media like cytosol, for those biomedical applications that require smaller particle sizes

The Atapuerca sites and the Ibeas hominids

The Atapuerca railway Trench and Ibeas sites near Burgos, Spain, are cave fillings that include a series of deposits ranging from below the Matuyama/Bruhnes reversal up to the end of Middle Pleistocene. The lowest fossil-bearing bed in the Trench contains an assemblage of large and small Mammals including Mimomys savini, Pitymys gregaloides, Pliomys episcopalis, Crocuta crocuta, Dama sp. and Megacerini; the uppermost assemblage includes Canis lupus, Lynx spelaea, Panthera (Leo) fossilis, Felis sylvestris, Equus caballus steinheimensis, E.c. germanicus, Pitymys subtenaneus, Microtus arvalis agrestis, Pliomys lenki, and also Panthera toscana, Dicerorhinus bemitoechus, Bison schoetensacki, which are equally present in the lowest level. The biostratigraphic correlation and dates of the sites are briefly discussed, as are the paleoclimatic interpretation of the Trench sequences. Stone artifacts are found in several layers; the earliest occurrences correspond to the upper beds containing Mimomys savini. A set of preserved human occupation floors has been excavated in the top fossil-bearing beds. The stone-tool assemblages of the upper levels are of upper-medial Acheulean to Charentian tradition. The rich bone breccia SH, in the Cueva Mayor-Cueva del Silo, Ibeas de Juarros, is a derived deposit, due to a mud flow that dispersed and carried the skeletons of many carnivores and humans. The taxa represented are: Vrsus deningeri (largely dominant), Panthera (Leo) fossilis, Vulpes vulpes, Homo sapiens var. Several traits of both mandibular and cranial remains are summarized. Preliminary attempts at dating suggest that the Ibeas fossil man is older than the Last Interglacial, or oxygen-isotope stage 5

Terahertz spin currents and inverse spin Hall effect in thin-film heterostructures containing complex magnetic compounds

Terahertz emission spectroscopy (TES) of ultrathin multilayers of magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport and spin–orbit interaction at highest frequencies, but has also paved the way for applications such as efficient and ultrabroadband emitters of terahertz (THz) electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable figure of merit, we systematically compare the strength of THz emission from X/Pt bilayers with X being a complex ferro-, ferri- and antiferromagnetic metal, that is, dysprosium cobalt (DyCo5), gadolinium iron (Gd24Fe76), magnetite (Fe3O4) and iron rhodium (FeRh). We find that the performance in terms of spin-current generation not only depends on the spin polarization of the magnet’s conduction electrons, but also on the specific interface conditions, thereby suggesting TES to be a highly interface-sensitive technique. In general, our results are relevant for all applications that rely on the optical generation of ultrafast spin currents in spintronic metallic multilayers