Abstract-Ultrafast Light-driven Simultaneous Excitation of Coherent Terahertz Magnons and Phonons in Multiferroic BiFeO3

Pritam Khan, Masataka Kanamaru, Keita Matsumoto, Toshimitsu Ito, Takuya Satoh

https://arxiv.org/abs/2002.07449

The ultrafast switching of magnetization in multiferroic materials by a femtosecond laser could provide various advantages in photonics and magnonics. An efficient approach to control the light matter interaction is the modulation of ultrafast coherent magnons and phonons in the high frequency range. Spontaneous Raman and infrared spectra reveal the excitation of magnons and optical phonons in multiferroic BiFeO3 in the sub few terahertz range. However, coherent control of such quasiparticles has not been achieved yet. In this study, we demonstrate that linearly polarized laser pulses simultaneously excite coherent magnons out of plane and in plane cyclone modes and optical phonon E mode in BiFeO3. Experimental results in conjugation with phenomenological theory, by considering three uniformly distributed magnetic domains reveal that impulsive stimulated Raman scattering is responsible for the generation of coherent magnons and phonons in BiFeO3. The observation of these terahertz magnon and optical phonon modes paves the way for the development of ultrafast magneto electro optical devices.

Abstract-Temperature Dependence of Magnetic Excitations: Terahertz Magnons above the Curie Temperature

H.J. Qin, Kh. Zakeri, A. Ernst, J. Kirschner

(Submitted on 20 Feb 2017)

https://arxiv.org/abs/1702.06104v1

When an ordered spin system of a given dimensionality undergoes a second order phase transition the dependence of the order parameter i.e. magnetization on temperature can be well-described by thermal excitations of elementary collective spin excitations (magnons). However, the behavior of magnons themselves, as a function of temperature and across the transition temperature TC, is an unknown issue. Utilizing spin-polarized high resolution electron energy loss spectroscopy we monitor the high-energy (terahertz) magnons, excited in an ultrathin ferromagnet, as a function of temperature. We show that the magnons' energy and lifetime decrease with temperature. The temperature-induced renormalization of the magnons' energy and lifetime depends on the wave vector. We provide quantitative results on the temperature-induced damping and discuss the possible mechanism e.g., multi-magnon scattering. A careful investigation of physical quantities determining the magnons' propagation indicates that terahertz magnons sustain their propagating character even at temperatures far above TC.

Abstract-Long-living terahertz magnons in ultrathin metallic ferromagnets

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• H. J. Qin,
• Kh. Zakeri,
• A. Ernst,
• L. M. Sandratskii,
• P. Buczek,
• A. Marmodoro,
• T. -H. Chuang,
• Y. Zhang
• & J. Kirschner
• • http://www.nature.com/ncomms/2015/150127/ncomms7126/full/ncomms7126.html

The main idea behind magnonics is to use the elementary magnetic excitations (magnons) for information transfer and processing. One of the main challenges, hindering the application of ultrafast terahertz magnons in magnonics, has been the short lifetime of these excitations in metallic ferromagnets. Here, we demonstrate that the engineering of the electronic structure of a ferromagnetic metal, by reducing its dimensionality and changing its chemical composition, opens a possibility to strongly suppress the relaxation channels of terahertz magnons and thereby enhance the magnons’ lifetime. For the first time, we report on the long-lived terahertz magnons excited in ultrathin metallic alloy films. On the basis of the first-principles calculations, we explain the microscopic nature of the long lifetime being a consequence of the peculiar electronic hybridizations of the species. We further demonstrate a way of tailoring magnon energies (frequencies) by varying the chemical composition of the film.