Dynamics of mesoscopic spins quantum effects

Información del proyecto

Identificador del acuerdo de subvención: FMBI961347

Fecha de inicio

Fecha de finalización

Financiado con arreglo a

• Specific research and technological development programme in the field of the training and mobility of researchers, 1994-1998

Coste total

Sin datos

Aportación de la UE

Sin datos

Coordinado por

Aristotle University of Thessaloniki
Greece

Objetivo

Magnetic tunneling has been a subject of intensive recent theoretical and ex- perimental study. Wernsdorfer et al. have recently reported the first observation of the magnetization of a single monodomain particle patterned by electron-beam lithography, together with a micro-bridge dc-SQUID deposited onto or next to the particle: a set-up that allows accurate measurements of the dynamical behavior of about 105 spins. Future improvements will allow measuring a reduced number of spins (103). Moreover, molecular magnetic materials with metallic clusters consti- tute themselves an additional mean to study particles with a really small number of spins (10 or 20). This will also enable a better understanding of the quantum - classical crossover. A phonon assisted quantum tunneling of an S = 10 spin is suggested to take place in a Mnl2 cluster material (16). An advantage of this crystalline system is that its translational invariance opens new possibilities for studying the dynamics by powerfull experimental methods such as neutron and muon spectroscopy. - One of the fundamental aims of this postdoctoral project is a better under- standing of the role that environmental effects play on Quantum Tunneling on the basis of the experimental findings. - MQT tunneling of the collective spin of submicronic particles will be inves- tigated using the spin coherent state path integral method. Exhaustive exper- imental investigations on submicronic particle using the micro-Squid technique were recently carried out. Squared hysteresis loops are obtained with a single magnetization jump at a switching field Hc. A statistical distribution of values was obtained in which the average shows deviations from a thermal activation model at temperatures lower than 1K. This was interpreted as a manifestation of MQT. On the other hand, the width of the switching field distribution when corrected from field sweeping rate, led to a temperature dependence that is unre- lated to thermal or quantum statistical fluctuations, and which is ascribed to the non rigidity of the internal magnetization density. Accordingly, the internal spin degree of freedom has to be taken into account to really understand the dynamics of the collective spin of the particle in these experiment. One way to tackle this difficult problem is by using the barrier fluctuations concept. Measurements of the distribution of the switching time show that the relaxation of the collective spin follows an stretched exponential behavior, indicating that this is a dynamical process in which the potential barriers are changing at the same time. We will also attempt to develop a stochastic approach suggested by the random character of the involved variable. Non linear effects and chaotic behavior should be expected. - The last aspect of our proporsal will concern the quantum behavior of clusters whose dynamics, in the classical limit of infinite spin, is chaotic.

Ámbito científico (EuroSciVoc)

• ciencias naturales › ciencias físicas › física atómica
• ciencias naturales › ciencias físicas › óptica › espectroscopia

Programa(s)

• FP4-TMR - Specific research and technological development programme in the field of the training and mobility of researchers, 1994-1998

Tema(s)

• 0302 - Post-doctoral research training grants

Convocatoria de propuestas

Datos no disponibles

Régimen de financiación

Datos no disponibles

Coordinador

Aristotle University of Thessaloniki

• Aportación de la UE: Sin datos
• Dirección: Analytical Chemistry Lab ; 54006 Thessaloniki ; Grecia
• Coste total: Sin datos