Graphene/ferromagnet interfaces have exhibited various unusual spin-orbit coupling(SOC) related effects despite very small SOC strength of graphene[1-3]. Here we have investigated femtosecond laser induced spin dynamics using an all-optical time-resolved magneto-optical Kerr effect(TR-MOKE) magnetometry in sputter-deposited CoFeB thin films on chemical-vapor-deposition grown single-layer graphene(SLG) by varying the thickness of CoFeB from 1.5 to 6 nm[4]. The ultrafast demagnetization time(τm) extracted using three-temperature modelling(Fig. 1(a)) show a monotonic variation with CoFeB thickness(Fig. 1(b)). The Gilbert damping parameter(α) is directly extracted from the decaying amplitude of precessional oscillation(Fig. 1(c)). We have modelled the CoFeB-thickness-dependent α to estimate the effective spin-mixing conductance(Geff) and two-magnon scattering coefficient(βTMS) for SLG/CoFeB interface(Fig. 1(d)) which revealed spin pumping(SP) [4] as the dominant contributor to modulation of α(Fig. 1(e)). Furthermore, we have observed an inverse relationship between τm and α for SLG/CoFeB heterostructures(Fig. 1(f)) due to the dominance of SP-induced nonlocal spin-transport mechanism[4]. To disentangle other possible interface contributions to the damping such as spin memory loss(SML), we have inserted a 1-nm-thick Cu spacer layer between the SLG and CoFeB. Negligible damping modulation by the insertion of Cu spacer between SLG and CoFeB confirms that additional effects like SML are absent in our system. In summary, this study has provided a qualitative understanding of different ultrafast spin manipulation mechanisms in a graphene-based heterostructure, which can lead towards the next-generation graphene-based ultrafast spintronics devices. AB acknowledges the financial assistance from S. N. Bose National Centre for Basic Sciences(SNBNCBS), India under Project SNB/AB/11-12/96 and SNB/AB/18-19/211. SNP, SM, SC and ArB acknowledge SNBNCBS for respective fellowship.

![](https://assets.underline.io/uploads/markdown_image/1/image/2365a212e2a849241df3b94e8286c456.jpg)

Fig. 1(a) Ultrafast demagnetization in SLG/CoFeB(d) (b) Evolution of τm with d (c) Precessional oscillations at H=3.59 kOe (d) Evolution of α fitted with a phenomenological model (e) Variation of 1/τm as a function of α (f) Contributions of SP and TMS to α.

Correlation between Femtosecond Laser Induced Spin Current and Spin Dynamics at the Single Layer Graphene/CoFeB Thin Films

Strong coupling between magnons and different quantum particles was studied extensively for quantum electrodynamics in the past few years. In this system, magnons in magnetic materials with high spin density are utilized where the “coupling strength” is collectively enhanced by square root of number of spins (N) to overcome the weaker coupling strength between individual spins and the microwave field. However, the strongly magnon-magnon [1] couplings in a confined nanomagnet remains to be revealed which is important for on chief intregration of hybride system. Here, we report the interaction between different magnon modes [2] in a magnetic dot array. The intermodal coupling in the strong coupling regime was approached with a maximum coupling strength of 0.745 GHz and cooperativity of 2.5. Furthermore, it is found that the coupling strength is highly dependent on the orientation of bias field. Micromagnetic simulation reveals that the compitetion between external bias field and inter dot dipolar interaction create a movement of domain in between the dot which results the anticrossing. The tunable coupling strength with the strength and orientation of bias field opens the opportunity of extremely controlled hybrid magnonic devices. This findings could greatly enrich the still evolving field of quantum magnonics.

![](https://assets.underline.io/uploads/markdown_image/1/image/1000a626fbb67c2a7ac444f1916e06d6.jpg)

Figure 1: (a) Bias field (Hext) dependent spin wave (SW) absorption spectra of NiFe nanodot lattice are shown at φ = 45°. (b) Distribution of internal at 400 Oe bias field strength along the 45 degree orientation (φ = 45°). The color map for the surface plots and internal field profile with the schematic of the external applied field (Hext) are given at the bottom right corner of the figure.

Strong Magnon-Magnon Coupling in Two-Dimensional Diamond Shaped Ferromagnetic Nanodots Array

**Session chair:** Gregory Malinowski, Institut Jean Lamour, Université de Lorraine



HOB - Femtosecond Excitation of Magnetism

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

**Session chair:** Axel Hoffmann, University of Illinois at Urbana-Champaign


Sudip Majumder

2

11

SHORT BIO

Presentations

Correlation between Femtosecond Laser Induced Spin Current and Spin Dynamics at the Single Layer Graphene/CoFeB Thin Films

Strong Magnon-Magnon Coupling in Two-Dimensional Diamond Shaped Ferromagnetic Nanodots Array

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