El artefacto sonoro más antiguo del Perú: aclaración de un dato histórico

In this paper we explain the inexact date of the oldest archaeological sonorous object from Peru; a date that was frequently utilized in the latter three decades. The object, a flute of wood excavated by Engel in Chilca and now at The Agrarian University Museum, has not 7000 years B.P.En un anterior trabajo (Mansilla 2007) dejamos pendiente la tarea de revisar el material del Dr. Fréderic Engel, depositado en el Museo de Arqueología y Agricultura Precolombina del Centro de Investigación de Zonas Áridas [CIZA] de la Universidad Agraria, con la finalidad de documentar y esclarecer la datación histórica del antecedente sonoro más antiguo en el Perú. Ahora estamos en condiciones de aclarar el fechado inexacto que, con frecuencia, se ha venido utilizando en las últimas tres décadas: el objeto sonoro arqueológico más antiguo hallado en el Perú, una flauta de madera excavada por Engel en Chilca, no tiene 7.000 años de antigüedad

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness $d_{cr}\sim 30$ nm the presence of an out of plane anisotropy induces the formation of stripes, while for $d<d_{cr}$ planar domains occur. Magnetic interactions have been characterized using the well known DCD-IRM remanence protocols, $\delta M$ plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, $\langle V_{ac}\rangle \sim 1.37\times 10^{4}$ nm$^{3},$ which is approximately independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure

Magnetoresistance in Fe1−x_{1-x}Gax_x thin films presenting striped magnetic pattern: the role of closure domains and domain walls

In this work we show the existence of closure domains in Fe$_{1-x}$Ga$_x$ thin films featuring a striped magnetic pattern and study the effect of the magnetic domain arrangement on the magnetotransport properties. By means of X-ray resonant magnetic scattering, we experimentally demonstrate the presence of such closure domains and estimate their sizes and relative contribution to surface magnetization. Magnetotransport experiments show that the behavior of the magnetoresistance depends on the measurement geometry as well as on the temperature. When the electric current ows perpendicular to the stripe direction, the resistivity decreases when a magnetic field is applied along the stripe direction (negative magnetoresistance) in all the studied temperature range, and the calculations indicate that the main source is the anisotropic magnetoresistance. In the case of current flowing parallel to the stripe domains, the magnetoresistance changes sign, being positive at room temperature and negative at 100 K. To explain this behavior, the contribution to magnetoresistance from the domain walls must be considered besides the anisotropic one.Comment: 8 pages, 5 figure

Controlling the dominant magnetic relaxation mechanisms for magnetic hyperthermia in bimagnetic core-shell nanoparticles

We report a simple and effective way to control the heat generation of a magnetic colloid under alternate magnetic fields by changing the shell composition of bimagnetic core-shell Fe 3 O 4 /Zn x Co 1-x Fe 2 O 4 nanoparticles. The core-shell structure constitutes a magnetically-coupled biphase system, with an effective anisotropy that can be tuned by the substitution of Co 2+ by Zn 2+ ions in the shell. Magnetic hyperthermia experiments of nanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brown relaxation mechanism in samples with higher anisotropy (i.e., larger concentration of Co within the shell) yielding high specific power absorption values in low viscosity media as hexane. Increasing the Zn concentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Néel relaxation that dominates the process when the nanoparticles are dispersed in a high-viscosity medium. We demonstrate that tuning the Zn contents at the shell of these exchange-coupled core/shell nanoparticles provides a way to control the magnetic anisotropy without loss of saturation magnetization. This ability is an essential prerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present. This journal i

pSESYNTH project: Community mobilization for a multi-disciplinary paleo database of the Global South

How to enhance paleoscientific research, collaboration and application in the Global South? The INQUA-funded multi-year pSESYNTH project envisions the first multi-disciplinary Holocene paleo database through a collaborative vision for past human-environmental systems in the Global South, and their future sustainability

Magnetic relaxation measurements of (alpha)-Fe2O3 antiferromagnetic particles below 1 K

In this paper we report magnetic relaxation data for antiferromagnetic a-Fe2O3 particles of 5-nm mean diameter in the temperature range 0.1–25 K. The average spin value of these particles S.124 and the uniaxial anisotropy constant D.1.631022 K have been estimated from the experimental values of the blocking temperature and anisotropy field. The observed plateau in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of spin tunneling from the ground state SZ5S. However, the scaling M vs T ln(n0t) is broken below 5 K, suggesting the occurrence of tunneling from excited states below this temperature