Macroscopic quantum tunneling

Leggett, A., Macroscopic Quantum Tunnelling and Related Matters, Proc. 18th Int. Conf. on Low Temperature Physics, Jpn. J. Appl. Phys. 26-Suppl. 26-3 1986 (1987). 

In this section, we concentrate on the fundamental impact of particle size reduction on magnetization processes in individual particles. Although not directly related to coercivity, the classical effect of single domain particle formation is described. At small particle size, reversal by coherent rotation tends to be favoured with respect to nucleation/pinning-depinning finally thermal activation effects and macroscopic quantum tunnelling are discussed. 

Wemsdorfer W, Orozco EB, Hasselbach K, Benoit A, Mailly D, Knbo O, Nakano H, Barbara B (1997b) Macroscopic quantum tunneling of magnetization of single ferrimagnetic nanoparticles of barinm ferrite. Phys Rev Lett 79 4014-4017... 

Neel-Brown model however, the nonlinear held effects have also been very significant. The further search for the accurate description of the macroscopic quantum tunneling of magnetization M needs correct asymptotic formulas for the reversal time for magnetocrystalline anisotropy potentials, which have been calculated by Coffey and collaborators as well [315-318]. 

E. M. Chudnovsky and J. Tejada, Macroscopic Quantum Tunneling of the Magnetic Moment, Cambridge University Press, Cambridge, England, 1998. 

ZENO AND ANTI-ZENO EFFECTS IN DRIVEN JOSEPHSON JUNCTIONS CONTROL OF MACROSCOPIC QUANTUM TUNNELING... 

Recently, new interesting phenomena, from both fundamental and technological points of view, exhibited by fine magnetic particles have attracted much attention, for example, macroscopic quantum tunneling of the magnetization, magnetocaloric effectwell above liquid helium... 

Macroscopic quantum tunneling, that is, the tunneling of a microscopic variable through the barrier between two minima of the effective potential of a macroscopic system, represents one of the most fascinating phenomena in condensed matter physics. It is well known that quantum phenomena can take place at the macroscopic scale " in systems with negligible dissipation (i.e., small interaction of the tunneling variable with the environment), for example, superconductors, " one-dimensional metals,and so forth. 

Figure G.l. Switching rate as a function of temperature for both thermal activation (TA) and macroscopic quantum tunneling (MQT). The crossover from the TA regime to the MQT regime takes place at temperature (Reproduced with permission from Ref. 358.)...

Results in favor of the existence of macroscopic quantum tunneling of the magnetization were also reported by means of low-temperature measurements of the frequency-dependent magnetic noise S co) and... 

Thomas L, Lionti FR, BaUow R, Gatteschi D, Sessoli R, Barbara B (1996) Macroscopic quantum tunnelling of magnetization in a single crystal of nanomagnets. Nature 383 145... 

La20s is an important lanthanum oxide, which is widely used in various types of catalytic reactions like dehydrogenation, combustion, hydrogenation, selective oxidation, etc. The nanomaterials (nano-sized materials or nano ultrafine particle) are denoted as the materials with the particle size in the range of 1-100 nm. Due to the quantum size effect, small size effect, siuface effect and macroscopic quantum tunneling effect, nano ultrafine materials have become the hotspot in the researches of catalysts [9]. In comparison with micro-sized lanthanum oxide, the nano-sized one, due to its higher specific surface area, has exhibited outstanding catalytic properties [10],... 

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