Effects of quantum mechanics on the deflagration threshold in the molecular magnetMn12acetate

Magnetic deflagration inGd5Ge4

“…This process is driven by the heat conductance and it closely resembles the magnetic deflagration observed in molecular magnets and manganites. [22][23][24][25][26][27][28][29] The dependence of avalanches on the initial state, initial temperature, and magnetic field agrees with the theory of deflagration. 30 Since magnetic transition in Gd 5 Ge 4 also involves structural transformation, it represents an interesting example of the magnetostructural deflagration.…”

“…This avalanche-like process, that occurs when the field reaches a certain value, has striking similarity with avalanches observed in the magnetization curves of molecular magnets [15][16][17][18] and of some manganites. [19][20][21] The latter avalanches have been investigated and successfully described [22][23][24][25][26][27][28][29] within theory of magnetic deflagration. 30 Deflagration is a physical term for slow burning that occurs, e.g., in a combustion engine when a chemical reaction in the fuel-air mixture is ignited by a spark of fire.…”

Anisotropic magnetic deflagration in single crystals of Gd5Ge4

“…6 Historically, such magnetic discontinuities have been called magnetic avalanches and they have been also observed in other materials [21][22][23][24][25][26][27][28] which also exhibit a giant magnetocaloric effect 24,29 related to a transition from a kineticallyarrested state to magnetic equilibrium 4,30 . The dynamics of the magnetization of the sample during such transitions have been reported first in molecular magnets [31][32][33][34][35][36][37][38][39] , and later in manganites [40][41][42] and polycrystalline samples of Gd 5 Ge 4 43 . For all these materials it was found that a phase-transition front forms and burns as a consequence of the energy difference between the initial and final states involved, and then it propagates through the sample at a constant speed on the order of a few m/s according to a heat diffusion process (see Appendix A for the basics of the theory of this phenomenon 44 and the definition of the different physical magnitudes involved).…”

“…In the case of molecular magnets, the speed of the deflagration front is determined by the value of the magnetic field applied along the easy magnetization axis, whereas the transverse field affects the threshold conditions [see for example ref. 38] via their unusual quantum properties 46,47 . In the case of manganites, as well as polycrystalline samples of Gd 5 Ge 4 , there is no influence, excluding geometrical effects, of the direction of the applied magnetic field on the properties of the deflagration process, whose observed characteristics are the result of averaging the properties along the principal crystallographic axes of the sample due to their random distribution.…”

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

“…15 In turn, these avalanche phenomena have themselves become the focus of much recent attention in Mn 12 -acetate. 16,[47][48][49][50] More dramatically, it has been shown by Morello et al, 51,52 that the coupled nuclear spin-lattice dynamics is strongly influenced by the FR species in the low-temperature regime where the SR molecules are completely blocked and, thus, should not mediate any coupling between the nuclear spins and the lattice. Therefore, these findings motivated more detailed spectroscopic investigations, as described in this article.…”