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Time-dependent spin and transport properties of a single-molecule magnet in a tunnel junction
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 5, article id 054311Article in journal (Refereed) Published
Abstract [en]

In single-molecule magnets, the exchange between a localized spin moment and the electronic background provides a suitable laboratory for studies of dynamical aspects of both local spin and transport properties. Here we address the time evolution of a localized spin moment coupled to an electronic level in a molecular quantum dot embedded in a tunnel junction between metallic leads. The interactions between the localized spin moment and the electronic level generate an effective interaction between the spin moment at different instances in time. Therefore, we show that, despite being a single-spin system, there are effective contributions of isotropic Heisenberg and anisotropic Ising and Dzyaloshinski-Moriya character acting on the spin moment. The interactions can be controlled by gate voltage, voltage bias, the spin polarization in the leads, in addition to external magnetic fields. Signatures of the spin dynamics are found in the transport properties of the tunneling system, and we demonstrate that measurements of the spin current may be used for readout of the local spin moment orientation.

Place, publisher, year, edition, pages
2016. Vol. 94, no 5, article id 054311
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-307890DOI: 10.1103/PhysRevB.94.054311ISI: 000381599100001OAI: oai:DiVA.org:uu-307890DiVA, id: diva2:1048805
Funder
Swedish Research CouncilAvailable from: 2016-11-22 Created: 2016-11-22 Last updated: 2018-12-05Bibliographically approved
In thesis
1. Dynamics of Magnetic Molecules under Electrical Control
Open this publication in new window or tab >>Dynamics of Magnetic Molecules under Electrical Control
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis theoretically studies the dynamics of molecular magnets under electrical control. Molecular magnets are nanoscale magnets that can, e.g., consist of single-molecules or single-atoms. In these magnets, the electronically mediated exchange and transport can be controlled by external fields. In this thesis, we study the effect of electrical control and voltage pulses on the transport properties, spin dynamics and the exchange of the molecular magnets.

Nonequilibrium Green's functions is the method used to describe the underlying electronic structure of the magnetic molecule. The studied systems consists of single-molecule magnets in a tunnel junction between metallic leads. Here, the transport characteristics are derived for charge, spin and heat currents in the system for time-dependent voltage pulses. Furthermore, a generalized spin equation of motion is derived for the molecular spin moment, using nonequilibrium field theory. The equation of motion incorporates nonequilibrium conditions and is of nonadiabatic character. The effective model for the spin moment can be decomposed into effective magnetic field, isotropic Heisenberg interaction, and anisotropic Ising and Dzyaloshinskii-Moriya interactions. These effective fields depends on the electronic structure of the molecule and can be controlled by, e.g., gate and bias voltages.

The thesis encompasses studies on the effect of a sudden on-set of a voltage pulse for a single-molecule magnet and its effect on the spin dynamics and transport properties of the molecule. Different approximations schemes for the spin equation of motion and their regimes of validity are investigated. Moreover, spin-dependent signatures in the heat transport characteristics of the single-molecule magnet are connected to the dynamics of the molecular spin moment. A phase induced switching mechanism of the molecular moment is shown for voltage pulses of varying temporal length. In the stationary limit, it is shown that one can electrically control the interaction and transport of two molecular magnets in a series. Furthermore, investigations on the electrictronically mediated anisotropy in a vibrating single-molecule magnet show that the anisotropy can be tuned by a temperature difference or a voltage bias.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 92
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1751
Keywords
Molecular magnets, Spin dynamics, Non-adiabatic effects, Exchange interaction, Thermoelectricity
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-368542 (URN)978-91-513-0520-2 (ISBN)
Public defence
2019-02-01, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-01-09 Created: 2018-12-05 Last updated: 2019-02-13

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