Phonon-Induced Quantum Magnetic Deflagration in Mn12

A comprehensive set of experiments on the effect of high-frequency surface acoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We have studied the quantum magnetic deflagration induced by SAWs under various experimental conditions extending the data shown in a very recent paper [A. Hernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused our study on the dependence of both the ignition time and the propagation speed of the magnetic avalanches on the frequency, amplitude, and duration of the SAW pulses in experiments performed under different temperatures and external magnetic fields.Comment: 7 pages, 9 figure

El Efecto túnel resonante de la magnetización a escala macroscópica abre las puertas de la computación cuántica

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Tunneling Splittings in Mn12-Acetate Single Crystals

A Landau-Zener multi-crossing method has been used to investigate the tunnel splittings in high quality Mn$_{12}$-acetate single crystals in the pure quantum relaxation regime and for fields applied parallel to the magnetic easy axis. With this method several individual tunneling resonances have been studied over a broad range of time scales. The relaxation is found to be non-exponential and a distribution of tunnel splittings is inferred from the data. The distributions suggest that the inhomogeneity in the tunneling rates is due to disorder that produces a non-zero mean value of the average transverse anisotropy, such as in a solvent disorder model. Further, the effect of intermolecular dipolar interaction on the magnetic relaxation has been studied.Comment: Europhysics Letters (in press). 7 pages, including 3 figure

Millikelvin magnetic relaxation measurements of alpha-Fe2O3 antiferromagnetic particles

In this paper we report magnetic relaxation data for antiferromagnetic alpha-Fe2O3 particles of 5 nm mean diameter in the temperature range 0.1 K to 25 K. The average spin value of these particles S=124 and the uniaxial anisotropy constant D=1.6x10^-2 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 Sz = S. However, the scaling M vs Tln(nu t) is broken below 5 K, suggesting the occurrence of tunneling from excited states below this temperature.Comment: 4 pages (two columns), 4 figure

Tunable crossover between one- and three-dimensional magnetic dynamics in C oII single-chain magnets organized by halogen bonding

Low-temperature magnetometry, ac susceptibility, and calorimetry have been employed to study Co-based single-chain magnets (SCMs) organized through halogen bonding. Magnetic hysteresis and maxima in the dc and ac susceptibilities, respectively, confirm the SCM behavior of the system. Several characteristic magnetic relaxation regimes are observed at different temperatures, which can be associated with both intra- and interchain exchange interactions. Remarkably, tweaking the rate at which an external magnetic field is swept along the axis of the chains enables a controlled transition between the one- and three-dimensional dynamics. Experiments on an isostructural Co-based SCM system crystallized with different halogens do not show three-dimensional dynamics, illustrating the importance of halogen bonding on the control of interchain interactions

Evaluación del comportamiento mecánico de mezclas asfálticas templadas con 100 % de material reciclado

The use of Half Warm Mixes with high Reclaimed Asphalt content (HWMRA) has the potential to generate significant environmental advantages such as the reduction in consumption of natural resources and the emission of gases into the atmosphere. This paper therefore focuses on demonstrating the viability of using these types of mixes in wearing courses. For this purpose, an HWMRA with 70 % and 100 % Reclaimed Asphalt Pavement (RAP) and emulsion were designed in the laboratory. The performance of the mixes was then assessed and compared with that of conventional Hot Mix Asphalt. In a second stage, the mixes were manufactured in-plant, and laid and compacted in an Accelerated Pavement Test track. The cores were then extracted and tested for stiffness modulus and resistance to fatigue. The results from the tests conducted with both the laboratory specimens and the cores showed that the performance of HWMRA is comparable to that of HMA. These findings encourage greater confidence in promoting the use of these types of sustainable asphalt mixes.La utilización de mezclas asfálticas templadas con alto contenido de asfalto reciclado (HWMRA) conlleva ventajas medioambientales como la reducción del consumo de recursos naturales y la emisión de gases a la atmósfera. Este artículo se centra en mostrar la viabilidad de este tipo de mezclas para capas de rodadura. Para ello, se diseñaron mezclas HWMRA con 70 % y 100 % de asfalto reciclado en el laboratorio y se evaluó y comparó su comportamiento con una mezcla caliente convencional. En una segunda etapa, las mezclas fueron fabricadas en planta, extendidas y compactadas en una pista de ensayo acelerado de pavimentos. A continuación, se extrajeron testigos y se ensayaron para conocer su módulo de rigidez y resistencia a fatiga. Tanto los resultados de laboratorio como tras la fabricación en planta y puesta en obra mostraron que el comportamiento de mezclas HWMRA es comparable al de mezclas calientes convencionales. Dicha conclusión puede aportar confianza a este tipo de mezclas sostenibles promoviendo su mayor utilización