Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and inplane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration

Controlled nucleation of topological defects in the stripe domain patterns of Lateral multilayers with Perpendicular Magnetic Anisotropy: competition between magnetostatic, exchange and misfit interactions

Magnetic lateral multilayers have been fabricated on weak perpendicular magnetic anisotropy amorphous Nd-Co films in order to perform a systematic study on the conditions for controlled nucleation of topological defects within their magnetic stripe domain pattern. A lateral thickness modulation of period $w$ is defined on the nanostructured samples that, in turn, induces a lateral modulation of both magnetic stripe domain periods $\lambda$ and average in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer period and in-plane applied field, thin and thick regions switch independently during in-plane magnetization reversal and domain walls are created within the in-plane magnetization configuration coupled to variable angle grain boundaries and disclinations within the magnetic stripe domain patterns. This process is mainly driven by the competition between rotatable anisotropy (that couples the magnetic stripe pattern to in-plane magnetization) and in-plane shape anisotropy induced by the periodic thickness modulation. However, as the structural period $w$ becomes comparable to magnetic stripe period $\lambda$, the nucleation of topological defects at the interfaces between thin and thick regions is hindered by a size effect and stripe domains in the different thickness regions become strongly coupled.Comment: 10 pages, 7 figures, submitted to Physical Review

Riqueza de especies en un gradiente de herbivoría de vizcachas (Lagostomus maximus Hollister)

Effects of plains vizcachas on the species richness of plants in the semiarid scrub were studied in Uhue Calel National Park, Argentina, from May to December 1993. Vizcachas are colonial, herbivorous rodents, that live in communal burrows systems (vizcacheras), which are occupied for many generations. Each social group of vizcachas forages in an exclusive home range around the burrows. Species richness was measured at 4 active vizcacheras along belt transects (20 m x 90 m long) extending ou1ward from the burrow system into the ungrazed matrix. Total species richness increased with distance from the burrows and reached a plateau in the ungrazed matrix rather than at moderate levels of grazing as predicted from the intermediate disturbance hypothesis. This pattern was more similar to pattems predicted by a grazing model that considers evolutionary history and environment moisture.Se estudiaron los efectos de la herbivoría de vizcachas sobre la riqueza de especies vegetales en un ambiente de monte semiárido, el Parque Nacional Lihue Calel, Argentina, entre los meses de mayo y diciembre de 1993. Las vizcachas son roedores herbívoros y gregarios que viven en sistemas de cuevas -vizcacheras- ocupados por muchas generaciones. Cada grupo social pastorea en un área de actividad exclusiva alrededor de las cuevas. La riqueza de especies fue muestreada en 4 vizcacheras activas en 4 transectas (20 m x 90 m) que se extendían desde la vizcachera hasta el interior de la matriz no pastoreada. La riqueza total de especies aumentó con la distancia desde las cuevas, alcanzando máximos valores en la matriz, pero no a niveles moderados de pastoreo como es predicho por la hipótesis de disturbio intermedio. El patrón observado fue más similar al predicho por un modelo que considera la historia evolutiva y la humedad ambiental

Aluminización de aceros ferriticos-martensiticos (hcm-12a) mediante cvd-fbr

Los recubrimientos de Aluminio son bien conocidos por tener una buena resistencia a la oxidación y a la sulfidización debido a la formación de una capa protectora de alúmina. La Deposición Química en Fase de Vapor mediante Lecho Fluidizado (CVD-FBR), debido a que es un proceso en el que se consiguen altas trasferencias de masa y calor a bajas temperaturas de operación. Además, tiene la ventaja de que se trabaja a presión atmosférica. La deposición de recubrimientos de Al sobre el acero ferrítico (HCM-12A) ha sido desarrollada mediante CVD-FBR. Los parámetros iniciales del proceso fueron determinados por la simulación termodinámica del proceso con la ayuda del programa informático “Thermocalc software”

Extensive analysis of native and non-native Centaurea solstitialis L. populations across the world shows no traces of polyploidization

Centaurea solstitialis L. (yellow starthistle, Asteraceae) is a Eurasian native plant introduced as an exotic into North and South America, and Australia, where it is regarded as a noxious invasive. Changes in ploidy level have been found to be responsible for numerous plant biological invasions, as they are involved in trait shifts critical to invasive success, like increased growth rate and biomass, longer life-span, or polycarpy. C. solstitialis had been reported to be diploid (2n = 2x = 16 chromosomes), however, actual data are scarce and sometimes contradictory. We determined for the first time the absolute nuclear DNA content by flow cytometry and estimated ploidy level in 52 natural populations of C. solstitialis across its native and non-native ranges, around the world. All the C. solstitialis populations screened were found to be homogeneously diploid (average 2C value of 1.72 pg, SD = ±0.06 pg), with no significant variation in DNA content between invasive and non-invasive genotypes. We did not find any meaningful difference among the extensive number of native and non-native C. solstitialis populations sampled around the globe, indicating that the species invasive success is not due to changes in genome size or ploidy level

Experimental admixture among geographically disjunct populations of an invasive plant yields a global mosaic of reproductive incompatibility and heterosis

1. Invasive species have the ability to rapidly adapt in the new regions where they are introduced. Classic evolutionary theory predicts that the accumulation of genetic differences over time in allopatric isolation may lead to reproductive incompatibilities resulting in decreases in reproductive success and, eventually, to speciation. However, experimental evidence for this theoretical prediction in the context of invasive species is lacking. We aimed to test for the potential of allopatry to determine reproductive success of invasive plants, by experimentally admixing genotypes from six different native and non‐native regions of Centaurea solstitialis, an invasive forb for which preliminary studies have detected some degree of reproductive isolation between one native and non‐native region. 2. We grew plants under common garden conditions and outcrossed individuals originating from different source populations in the native and introduced range to evaluate reproductive success in terms of seed to ovule ratio produced. We also assessed geographical and genetic isolation among C. solstitialis regions as a potential driving factor of reproductive success. 3. Experimental admixture generated mixed fitness effects, including significant increases, decreases and no differences in reproductive success as compared to crosses within population (control). Centaurea solstitialis invasive populations in the Americas generated preponderantly negative fitness interactions, regardless of the pollen source, suggesting selection against immigrants and reinforcement. Other non‐native populations (Australia) as well as individuals from the native range of Spain demonstrated an increase in fitness for between‐region crosses, indicating inbreeding. These differences show an asymmetrical response to inter‐regional gene flow, but no evidence of isolation by distance. 4. Synthesis. The speed of adaptation and the accumulation of reproductive incompatibilities among allopatric populations of invasive species might be more rapid than previously assumed. Our data show a global mosaic of reproductive outputs, showcasing an array of evolutionary processes unfolding during colonization at large biogeographical scales

Nanoscale imaging of buried topological defects with quantitative X-ray magnetic microscopy

This work is licensed under a Creative Commons Attribution 4.0 International License.-- et al.Advances in nanoscale magnetism increasingly require characterization tools providing detailed descriptions of magnetic configurations. Magnetic transmission X-ray microscopy produces element specific magnetic domain images with nanometric lateral resolution in films up to ∼100 nm thick. Here we present an imaging method using the angular dependence of magnetic contrast in a series of high resolution transmission X-ray microscopy images to obtain quantitative descriptions of the magnetization (canting angles relative to surface normal and sense). This method is applied to 55-120 nm thick ferromagnetic NdCo 5 layers (canting angles between 65° and 22°), and to a NdCo 5 film covered with permalloy. Interestingly, permalloy induces a 43° rotation of Co magnetization towards surface normal. Our method allows identifying complex topological defects (merons or 1/2 skyrmions) in a NdCo 5 film that are only partially replicated by the permalloy overlayer. These results open possibilities for the characterization of deeply buried magnetic topological defects, nanostructures and devices.Work supported by Spanish MINECO under grant FIS2013-45469. A. Hierro-Rodriguez acknowledges support from FCT of Portugal (Grant SFRH/BPD/90471/2012). C. Blanco-Roldán thanks support from CSIC JAE Predoc Program.Peer Reviewe