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Magnetic detonation structure in crystals of nanomagnets controlled by thermal conduction and volume viscosity
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics. Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden.
Umeå University, Faculty of Science and Technology, Department of Physics.
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 9, 094428Article in journal (Refereed) Published
Abstract [en]

Experimentally detected ultrafast spin avalanches spreading in crystals of molecular (nano) magnets [Decelle et al., Phys. Rev. Lett. 102, 027203 (2009)] have recently been explained in terms of magnetic detonation [Modestov et al., Phys. Rev. Lett. 107, 207208 (2011)]. Here magnetic detonation structure is investigated by taking into account transport processes of the crystals such as thermal conduction and volume viscosity. The transport processes result in smooth profiles of the most important thermodynamical crystal parameters, temperature, density, and pressure, all over the magnetic detonation front, including the leading shock, which is one of the key regions of magnetic detonation. In the case of zero volume viscosity, thermal conduction leads to an isothermal discontinuity instead of the shock, for which temperature is continuous while density and pressure experience jump. It is also demonstrated that the thickness of the magnetic detonation front may be controlled by applying the transverse-magnetic field, which is important for possible experimental observations of magnetic detonation.

Place, publisher, year, edition, pages
2015. Vol. 91, no 9, 094428
National Category
Condensed Matter Physics
URN: urn:nbn:se:umu:diva-102360DOI: 10.1103/PhysRevB.91.094428ISI: 000351875300002OAI: diva2:825245
Available from: 2015-06-23 Created: 2015-04-23 Last updated: 2016-08-12Bibliographically approved
In thesis
1. Magnetic deflagration and detonation in crystals of nanomagnets
Open this publication in new window or tab >>Magnetic deflagration and detonation in crystals of nanomagnets
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis we cover the dynamics of the macro magnetic transformations (spin avalanches) in crystals of molecular nanomagnets, also known as magnetic deflagration and detonation.

Taking a single-molecule Hamiltonian, we calculate the dependence of Zeeman energy and the activation energy as a function of an external magnetic field at different angles relative to the easy axis of the crystal. Using quantum mechanical calculations, we show that the energy levels of the molecule exhibit complex behavior in presence of a transverse component of the magnetic field. For an arbitrarily aligned magnetic field, the energy levels do not arrange in a simple "double-well" manner. We extend existing theoretical models by generalizing the Zeeman energy for a wide range of magnetic fields and its different orientations.

We obtain a new type of front instability in magnetization-switching media. Due to the dipole-dipole interaction between the molecules magnetic instability results to the front banding and change in the front propagation velocity. The magnetic instability has a universal physical nature similar to the Darrieus-Landau instability. The instability growth rate and the cutoff length are calculated for the spin avalanches in the crystals of nanomagnets.

Finally, we investigate the internal structure of the magnetic detonation front. We calculate the continuous shock profile using the transport processes of the crystal such as thermal conduction and volume viscosity. Such an approach can be applied to any weak shock wave in solids. Zero volume viscosity leads to an isothermal jump, i.e., the temperature changes continuously while the pressure and the density experience discontinuity. The analysis has shown that the volume viscosity plays a major role in the formation of the detonation front.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 40 p.
Nanomagnets, magnetic deflagration, front instability, Zeeman energy, magnetic instability, magnetic detonation, weak detonation
National Category
Physical Sciences
Research subject
Physics Of Matter
urn:nbn:se:umu:diva-124445 (URN)978-91-7601-534-6 (ISBN)
Public defence
2016-09-05, MC413, MIT-huset, Umeå, 13:00 (English)
Available from: 2016-08-15 Created: 2016-08-11 Last updated: 2016-08-15Bibliographically approved

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