Excitation modes of vortices in sub-micron magnetic disks

Classical and quantum theory of spin waves in the vortex state of a mesoscopic sub-micron magnetic disk has been developed with account of the finite mass density of the vortex. Oscillations of the vortex core resemble oscillations of a charged string in a potential well in the presence of the magnetic field. Conventional gyroscopic frequency appears as a gap in the spectrum of spin waves of the vortex. The mass of the vortex has been computed that agrees with experimental findings. Finite vortex mass generates a high-frequency branch of spin waves. Effects of the external magnetic field and dissipation have been addressed.Comment: 12 page

Quantum dynamics of vortices in mesoscopic magnetic disks

Model of quantum depinning of magnetic vortex cores from line defects in a disk geometry and under the application of an in-plane magnetic field has been developed within the framework of the Caldeira-Leggett theory. The corresponding instanton solutions are computed for several values of the magnetic field. Expressions for the crossover temperature Tc and for the depinning rate \Gamma(T) are obtained. Fitting of the theory parameters to experimental data is also presented.Comment: 8 page

Quantum Nanomagnetism

In this paper we discuss some of our most important results in quantum nanomagnets in the last twenty years. We start with the tunnelling of the magnetic moment in single domain particles, then we will move to molecular magnets to explain both resonant spin tunnelling and quantum magnetic deflagration and we will finish discussing the quantum phenomena recently observed in vortices of two dimensional disks and in type I superconductors. Probably the most important question to answer in the cases presented in this paper refers to the possibility to detect both coherent phonons and photons from the demagnetization process of molecular magnets as well as the fact to go deeper in the quantum phenomena observed in vortices of two dimensional disks and in type I superconductors. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3535

Dissipative Macroscopic Quantum Tunneling in Type-I Superconductors

We study macroscopic quantum tunneling of interfaces separating normal and superconducting regions in type-I superconductors. Mathematical model is developed, that describes dissipative quantum escape of a two-dimensional manifold from a planar potential well. It corresponds to, e.g., a current-driven quantum depinning of the interface from a grain boundary or from artificially manufactured pinning layer. Effective action is derived and instantons of the equations of motion are investigated. Crossover between thermal activation and quantum tunneling is studied and the crossover temperature is computed. Our results, together with recent observation of non-thermal low-temperature magnetic relaxation in lead, suggest possibility of a controlled measurement of quantum depinning of the interface in a type-I superconductor.Comment: 6 pages, 2 figure