1
|
Grishunin KA, Bilyk VR, Mishina ED, Kimel AV, Mashkovich EA. Two-dimensional terahertz spectroscopy as a tool for revealing nonlinear interactions in media. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:073005. [PMID: 37498165 DOI: 10.1063/5.0138253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 06/27/2023] [Indexed: 07/28/2023]
Abstract
Usually, the presence of multiple eigenstates (magnons and phonons) in a system makes it difficult to analyze the coupled excitation mechanism using conventional single-pulse terahertz (THz) spectroscopy. On the contrary, 2D THz spectroscopy reveals energy flows between these states, which facilitates the identification of the coupled dynamics. In this article, we provide a theoretical description of this advanced technique and an experimental demonstration of its performance in antiferromagnet CoF2. Here, 2D THz spectroscopy shows that the THz pulse induces energy transfer from the magnon mode to the Raman-active phonon mode via a nonlinear excitation pathway.
Collapse
Affiliation(s)
- K A Grishunin
- Institute for Molecules and Materials, Radboud University, 6525AJ Nijmegen, The Netherlands
| | - V R Bilyk
- Institute for Molecules and Materials, Radboud University, 6525AJ Nijmegen, The Netherlands
- Department of Nanotechnology, MIREA - Russian Technological University, Prospekt Vernadskogo, 78, 119454 Moscow, Russia
| | - E D Mishina
- Department of Nanotechnology, MIREA - Russian Technological University, Prospekt Vernadskogo, 78, 119454 Moscow, Russia
| | - A V Kimel
- Institute for Molecules and Materials, Radboud University, 6525AJ Nijmegen, The Netherlands
| | - E A Mashkovich
- Institute of Physics II, University of Cologne, Cologne D-50937, Germany
| |
Collapse
|
2
|
Unikandanunni V, Medapalli R, Asa M, Albisetti E, Petti D, Bertacco R, Fullerton EE, Bonetti S. Inertial Spin Dynamics in Epitaxial Cobalt Films. PHYSICAL REVIEW LETTERS 2022; 129:237201. [PMID: 36563189 DOI: 10.1103/physrevlett.129.237201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Accepted: 11/09/2022] [Indexed: 06/17/2023]
Abstract
We investigate the spin dynamics driven by terahertz magnetic fields in epitaxial thin films of cobalt in its three crystalline phases. The terahertz magnetic field generates a torque on the magnetization which causes it to precess for about 1 ps, with a subpicosecond temporal lag from the driving force. Then, the magnetization undergoes natural damped THz oscillations at a frequency characteristic of the crystalline phase. We describe the experimental observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the results from the relativistic theory of magnetic inertia, we find that the angular momentum relaxation time η is the only material parameter needed to describe all the experimental evidence. Our experiments suggest a proportionality between η and the strength of the magnetocrystalline anisotropy.
Collapse
Affiliation(s)
| | - Rajasekhar Medapalli
- Center for Memory and Recording Research, University of California San Diego, San Diego, California 92093, USA
- Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, United Kingdom
| | - Marco Asa
- Department of Physics, Politecnico di Milano Technical University, 20133 Milano, Italy
| | - Edoardo Albisetti
- Department of Physics, Politecnico di Milano Technical University, 20133 Milano, Italy
| | - Daniela Petti
- Department of Physics, Politecnico di Milano Technical University, 20133 Milano, Italy
| | - Riccardo Bertacco
- Department of Physics, Politecnico di Milano Technical University, 20133 Milano, Italy
| | - Eric E Fullerton
- Center for Memory and Recording Research, University of California San Diego, San Diego, California 92093, USA
| | - Stefano Bonetti
- Department of Physics, Stockholm University, 10691 Stockholm, Sweden
- Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, 30172 Venice, Italy
| |
Collapse
|
3
|
Abstract
In past decades, ultrafast spin dynamics in magnetic systems have been associated with heat deposition from high energy laser pulses, limiting the selective access to spin order. Here, we use a long wavelength terahertz (THz) pump–optical probe setup to measure structural features in the ultrafast time scale. We find that complete demagnetization is possible with <6 THz pulses. This occurs concurrently with longitudinal acoustic phonons and an electronic response.
Collapse
|
4
|
Fallarino L, López Rojo E, Quintana M, Salcedo Gallo JS, Kirby BJ, Berger A. Modifying Critical Exponents of Magnetic Phase Transitions via Nanoscale Materials Design. PHYSICAL REVIEW LETTERS 2021; 127:147201. [PMID: 34652169 DOI: 10.1103/physrevlett.127.147201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 08/10/2021] [Indexed: 06/13/2023]
Abstract
We demonstrate a nanoscale materials design path that allows us to bypass universality in thin ferromagnetic films and enables us to tune the critical exponents of ferromagnetic phase transitions in a very wide parameter range, while at the same time preserving scaling in an extended phase space near the Curie temperature. Our detailed magnetometry results reveal that single crystal CoRu alloy films, in which the predefined depth dependent exchange coupling strength follows a V-shaped profile, exhibit critical scaling behavior over many orders of magnitude. Their critical exponents, however, can be designed and controlled by modifying their specific nanoscale structures, thus demonstrating full tunability of critical behavior. The reason for this tunability and the disappearance of universality is shown to be the competing relevance of collective versus interface propagating progression of ferromagnetic phase transitions, whose balance we find to be dependent on the specifics of the underlying exchange coupling strength profile.
Collapse
Affiliation(s)
| | - Eva López Rojo
- CIC nanoGUNE BRTA, E-20018 Donostia-San Sebastián, Spain
- Faculty of Science, University of Valladolid, E-47011 Valladolid, Spain
| | - Mikel Quintana
- CIC nanoGUNE BRTA, E-20018 Donostia-San Sebastián, Spain
| | | | - Brian J Kirby
- NIST Center for Neutron Research, Gaithersburg, Maryland 20899, USA
| | - Andreas Berger
- CIC nanoGUNE BRTA, E-20018 Donostia-San Sebastián, Spain
| |
Collapse
|
5
|
Soumah L, Bossini D, Anane A, Bonetti S. Optical Frequency Up-Conversion of the Ferromagnetic Resonance in an Ultrathin Garnet Mediated by Magnetoelastic Coupling. PHYSICAL REVIEW LETTERS 2021; 127:077203. [PMID: 34459643 DOI: 10.1103/physrevlett.127.077203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 06/07/2021] [Accepted: 07/19/2021] [Indexed: 06/13/2023]
Abstract
We perform ultrafast pump-probe measurements on a nanometer-thick crystalline Bi-doped yttrium iron garnet film with perpendicular magnetic anisotropy. Tuning the photon energy of the pump laser pulses above and below the material's band gap, we trigger ultrafast optical and spin dynamics via both one- and two-photon absorption. Contrary to the common scenario, the optically induced excitation induces an increase up to 20% of the ferromagnetic resonance frequency of the material. We explain this unexpected result in terms of a modification of the magnetic anisotropy caused by a long-lived photo-induced strain, which transiently and reversibly modifies the magnetoelastic coupling in the material. Our results disclose the possibility to optically increase the magnetic eigenfrequency in nanometer-thick magnets.
Collapse
Affiliation(s)
- Lucile Soumah
- Department of Physics, Stockholm University, 10691 Stockholm, Sweden
| | - Davide Bossini
- Department of Physics and Center for Applied Photonics, University of Konstanz, 78464 Konstanz, Germany
| | - Abdelmadjid Anane
- Unit Mixte de Physique CNRS, Thales, Université Paris-Sud, Université Paris Saclay, 91767 Palaiseau, France
| | - Stefano Bonetti
- Department of Physics, Stockholm University, 10691 Stockholm, Sweden
- Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, 30172 Venice, Italy
| |
Collapse
|
6
|
Zhang X, Chen Y, Zhao L, Tan Y, Zhang Q, Ma C, Harris VG. Giant low-field tunability of THz transmission in patterned magnetic split-ring metastructures. OPTICS EXPRESS 2020; 28:34035-34044. [PMID: 33182881 DOI: 10.1364/oe.409312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 10/17/2020] [Indexed: 06/11/2023]
Abstract
Mirror-asymmetric split-ring metamaterials with high quality factor in the terahertz (THz) band, consisting of patterned high magnetic permeability and low coercivity FeNHf films deposited on high resistivity silicon substrates, were studied for their magnetic field tunable response in frequency and transmission. Dynamic tuning of terahertz transmission and electromagnetic resonance modes were investigated theoretically and experimentally as a function of magnetization of the FeNHf film. Experimental results indicate that the metamaterial structure provides a giant tunability of resonance frequency (Δfr/fr=3.3%) and transmittivity (21%) at a frequency of 0.665 THz under a low magnetic field of H=100 Oe. Remarkable tuning coefficients of frequency and transmittivity, 0.23 GHz/Oe and 0.21%/Oe, respectively, were measured. Finite difference time domain simulations reveal that the incredible tunability stems predominately from the response of the THz dynamic magnetic field to magnetization. As a result, the metamaterial, consisting of a simple magnetic split-ring microstructure, provides previously unimagined paths to tunable devices for potential use in emerging THz technologies including 6G communication systems and networks.
Collapse
|