Effect of quantum tunneling on the ignition and propagation of magnetic avalanches inMn12acetate

Abstract

Using a wire heater to ignite magnetic avalanches in fixed magnetic field applied along the easy axis of single crystals of the molecular magnet Mn 12 acetate, we report fast local measurements of the temperature and time-resolved measurements of the local magnetization as a function of magnetic field. In addition to confirming maxima in the velocity of propagation, we find that avalanches trigger at a threshold temperature which exhibits pronounced minima at resonant magnetic fields, demonstrating that thermally assisted quantum tunneling plays an important role in the ignition as well as the propagation of magnetic avalanches in molecular magnets.

Magnetic deflagration inGd5Ge4

“…3 is due to the 22 kOe field applied each time before the avalanche was ignited.͒ There is a clear correlation between the two: The initial relaxation reduces "flammability" of the crystal. These results are similar to the results on molecular magnets 24,27 and on manganites. 25 In order to distinguish between the temperature rise due to the heat pulse itself and the temperature rise due to the avalanche we plotted Fig.…”

“…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.…”

Magnetic Avalanches in Molecular Magnets

“…McHugh et al [22] used a resistive wire element as a simple electric heater to trigger avalanches in a manner similar to the work of Paulsen and Park [1]. In these experiments, an external magnetic field is ramped to, and held at a fixed value.…”

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

“…Additionally, it has been also shown that the required temperature to ignite avalanche at particular values of the longitudinal field, h z , presents dips at resonant fields. 10 In this Brief Report we study the deflagration threshold in Mn 12 -Ac in a magnetic field applied at an angle with respect to the anisotropy axis. In a first approximation the magnetic Hamiltonian of the crystal is…”