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Deák A, Hinzke D, Szunyogh L, Nowak U. Role of temperature-dependent spin model parameters in ultra-fast magnetization dynamics. J Phys Condens Matter 2017; 29:314003. [PMID: 28580905 DOI: 10.1088/1361-648x/aa76fc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In the spirit of multi-scale modelling magnetization dynamics at elevated temperature is often simulated in terms of a spin model where the model parameters are derived from first principles. While these parameters are mostly assumed temperature-independent and thermal properties arise from spin fluctuations only, other scenarios are also possible. Choosing bcc Fe as an example, we investigate the influence of different kinds of model assumptions on ultra-fast spin dynamics, where following a femtosecond laser pulse, a sample is demagnetized due to a sudden rise of the electron temperature. While different model assumptions do not affect the simulational results qualitatively, their details do depend on the nature of the modelling.
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Affiliation(s)
- A Deák
- Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki út 8., HU-1111 Budapest, Hungary. MTA-BME Condensed Matter Research Group, Budapest University of Technology and Economics, Budafoki út 8., HU-1111 Budapest, Hungary
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Frietsch B, Bowlan J, Carley R, Teichmann M, Wienholdt S, Hinzke D, Nowak U, Carva K, Oppeneer PM, Weinelt M. Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal. Nat Commun 2015; 6:8262. [PMID: 26355196 PMCID: PMC4579838 DOI: 10.1038/ncomms9262] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 08/04/2015] [Indexed: 01/26/2023] Open
Abstract
The Heisenberg–Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale. Due the strength of the intra-atomic exchange interaction, it is generally assumed that alignment of spin moments in intra-atomic orbitals is quasi-instantaneous. Here, the authors demonstrate the breakdown of this relation between the 4f and 5d electrons in gadolinium following ultrashort optical excitation.
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Affiliation(s)
- B Frietsch
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - J Bowlan
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - R Carley
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - M Teichmann
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - S Wienholdt
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - D Hinzke
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - U Nowak
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - K Carva
- Department of Physics and Astronomy, Uppsala University, PO Box 516, 75120 Uppsala, Sweden.,Charles University, Faculty of Mathematics and Physics, DCMP, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic
| | - P M Oppeneer
- Department of Physics and Astronomy, Uppsala University, PO Box 516, 75120 Uppsala, Sweden
| | - M Weinelt
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Schlickeiser F, Ritzmann U, Hinzke D, Nowak U. Role of entropy in domain wall motion in thermal gradients. Phys Rev Lett 2014; 113:097201. [PMID: 25216002 DOI: 10.1103/physrevlett.113.097201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Indexed: 06/03/2023]
Abstract
Thermally driven domain wall (DW) motion caused solely by magnonic spin currents was forecast theoretically and has been measured recently in a magnetic insulator using magneto-optical Kerr effect microscopy. We present an analytical calculation of the DW velocity as well as the Walker breakdown within the framework of the Landau Lifshitz Bloch equation of motion. The temperature gradient leads to a torque term acting on the magnetization where the DW is mainly driven by the temperature dependence of the exchange stiffness, or--in a more general picture--by the maximization of entropy. The existence of this entropic torque term does not rest on the angular momentum transfer from the magnonic spin current. Hence, even DWs in antiferromagnets or compensated ferrimagnets should move accordingly. We further argue that the entropic torque exceeds that of the magnonic spin current.
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Affiliation(s)
- F Schlickeiser
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
| | - U Ritzmann
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
| | - D Hinzke
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
| | - U Nowak
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
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Wienholdt S, Hinzke D, Nowak U. THz switching of antiferromagnets and ferrimagnets. Phys Rev Lett 2012; 108:247207. [PMID: 23004319 DOI: 10.1103/physrevlett.108.247207] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Revised: 03/09/2012] [Indexed: 06/01/2023]
Abstract
Using analytical calculations as well as computer simulations, we show that antiferromagnets can be switched on a time scale of picoseconds using THz laser pulses only. This all-optically triggered switching mechanism rests on the coordinated dynamics of the two interacting sublattices with an inertial character. We calculate the resonance frequencies in the nonlinear regime, the orbits, and estimate the field strength required for switching analytically. Furthermore, we demonstrate that ferrimagnets can be switched similarly at their compensation point.
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Affiliation(s)
- S Wienholdt
- Fachbereich Physik, Universität Konstanz, Konstanz D-78457, Germany
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Heinen J, Hinzke D, Boulle O, Malinowski G, Swagten HJM, Koopmans B, Ulysse C, Faini G, Ocker B, Wrona J, Kläui M. Determination of the spin torque non-adiabaticity in perpendicularly magnetized nanowires. J Phys Condens Matter 2012; 24:024220. [PMID: 22172802 DOI: 10.1088/0953-8984/24/2/024220] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Novel nanofabrication methods and the discovery of an efficient manipulation of local magnetization based on spin polarized currents has generated a tremendous interest in the field of spintronics. The search for materials allowing for fast domain wall dynamics requires fundamental research into the effects involved (Oersted fields, adiabatic and non-adiabatic spin torque, Joule heating) and possibilities for a quantitative comparison. Theoretical descriptions reveal a material and geometry dependence of the non-adiabaticity factor β, which governs the domain wall velocity. Here, we present two independent approaches for determining β: (i) measuring the dependence of the dwell times for which a domain wall stays in a metastable pinning state on the injected current and (ii) the current-field equivalence approach. The comparison of the deduced β values highlights the problems of using one-dimensional models to describe two-dimensional dynamics and allows us to ascertain the reliability, robustness and limits of the approaches used.
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Affiliation(s)
- J Heinen
- Fachbereich Physik, Universität Konstanz, Konstanz, Germany
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Abstract
The recently discovered spin Seebeck effect refers to a spin current induced by a temperature gradient in a ferromagnetic material. It combines spin degrees of freedom with caloric properties, opening the door for the invention of new, spin caloritronic devices. Using spin model simulations as well as an innovative, multiscale micromagnetic framework we show that magnonic spin currents caused by temperature gradients lead to spin transfer torque effects, which can drag a domain wall in a ferromagnetic nanostructure towards the hotter part of the wire. This effect opens new perspectives for the control and manipulation of domain structures.
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Affiliation(s)
- D Hinzke
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
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Vahaplar K, Kalashnikova AM, Kimel AV, Hinzke D, Nowak U, Chantrell R, Tsukamoto A, Itoh A, Kirilyuk A, Rasing T. Ultrafast path for optical magnetization reversal via a strongly nonequilibrium state. Phys Rev Lett 2009; 103:117201. [PMID: 19792396 DOI: 10.1103/physrevlett.103.117201] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Revised: 07/28/2009] [Indexed: 05/06/2023]
Abstract
Using time-resolved single-shot pump-probe microscopy we unveil the mechanism and the time scale of all-optical magnetization reversal by a single circularly polarized 100 fs laser pulse. We demonstrate that the reversal has a linear character, i.e., does not involve precession but occurs via a strongly nonequilibrium state. Calculations show that the reversal time which can be achieved via this mechanism is within 10 ps for a 30 nm domain. Using two single subpicosecond laser pulses we demonstrate that for a 5 microm domain the magnetic information can be recorded and readout within 30 ps, which is the fastest "write-read" event demonstrated for magnetic recording so far.
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Affiliation(s)
- K Vahaplar
- Institute for Molecules and Materials, Radboud University Nijmegen, P.O. Box 9010 6500 GL Nijmegen, The Netherlands.
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