We use electrical detection, in combination with microwave transmission, to investigate both resonant and non-resonant magnon-photon coupling at room temperature. Spin pumping in a dynamically coupled magnon-photon system is found to be distinctly different from previous experiments. Characteristic coupling features such as modes anti-crossing, line width evolution, peculiar line shape, and resonance broadening are systematically measured and consistently analyzed by a theoretical model set on the foundation of classical electrodynamic coupling. Our experimental and theoretical approach pave the way for pursuing microwave coherent manipulation of pure spin current via the combination of spin pumping and magnon-photon coupling. PACS numbers:Coupling between electrodynamics and magnetization dynamics is a subject of cross-disciplinary and longstanding interest.The nuclear magnetic resonance (NMR) community has studied this effect for decades by measuring the radiation damping of NMR [1]. Engineers have routinely utilized this effect for designing microwave [2] and THz devices [3]. In condensed matter physics, such a coupling leads to the magnon polariton [4], which is an elementary excitation characterized by an intrinsic excitation gap between ferromagnetic resonance (FMR) and ferromagnetic antiresonance [5]. Extrinsically, classical coupling of magnetization dynamics with its electrodynamic surrounding causes Faraday induction of both NMR [6] and FMR [7]. From the perspective of quantum physics, resonant spin-photon coupling plays a central role in utilizing quantum information [8].In 2010, a theoretical work of Soykal and Flatté [9] sparked excitement in the community of spintronics for studying the strong field interaction of magnons and microwave photons. Pioneering experiments have been performed at cryogenic temperatures by Huebl et al. [10] and Tabuchi et al. [11] on the ferromagnetic insulator Yttrium iron garnet (YIG) placed on/in a microwave cavity, in which a large normal mode splitting was found in the transmission measurements, indicating large quantumcoherent magnon-photon coupling. In October 2014, an experimental breakthrough was made by Zhang et al.[12], who demonstrated Rabi-oscillations of the coupled magnon-photon system at room temperature. In the same month, an ultrahigh cooperativity of 10 5 between magnon and photon modes was reported [13]. These exciting works reveal just the tip of the iceberg of the new field of cavity spintronics. * Current affiliation: Department of Physics and Astronomy, University of Denver, Colorado, 80208, USA † Electronic address: hu@physics.umanitoba.ca; URL: http://www.physics.umanitoba.ca/∼hu So far, experiments in this emerging field were performed by measuring either the transmission (S 21 ) or reflection coefficient (S 11 ) of the microwave cavity loaded with a YIG sample. The coupling strength was obtained by fitting these S parameters to the microwave input-output formalism with an added self-energy term attributed to the magnon-photon coupling. This sta...

We report the first observation of the magnon-polariton bistability in a cavity magnonics system consisting of cavity photons strongly interacting with the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors are emerged as sharp frequency switchings of the cavity magnon-polaritons (CMPs) and related to the transition between states with large and small number of polaritons. In our experiment, we align, respectively, the [100] and [110] crystallographic axes of the YIG sphere parallel to the static magnetic field and find very different bistable behaviors (e.g., clockwise and counter-clockwise hysteresis loops) in these two cases. The experimental results are well fitted and explained as being due to the Kerr nonlinearity with either positive or negative coefficient. Moreover, when the magnetic field is tuned away from the anticrossing point of CMPs, we observe simultaneous bistability of both magnons and cavity photons by applying a drive field on the lower branch.

We report dissipative magnon-photon coupling caused by cavity Lenz effect, where the magnons in a magnet induce a rf current in the cavity, leading to a cavity back action that impedes the magnetization dynamics. This effect is revealed in our experiment as level attraction with a coalescence of hybridized magnon-photon modes, which is distinctly different from level repulsion with mode anticrossing caused by coherent magnon-photon coupling. We develop a method to control the interpolation of coherent and dissipative magnon-photon coupling, and observe a matching condition where the two effects cancel. Our work sheds light on the so-far hidden side of magnon-photon coupling, opening a new avenue for controlling and utilizing light-matter interactions.

)This work reviews and examines two particular issues related with the new technique of electrical detection of ferromagnetic resonance (FMR). This powerful technique has been broadly applied for studying magnetization and spin dynamics over the past few years. The first issue is the relation and distinction between different mechanisms that give rise to a photovoltage via FMR in composite magnetic structures, and the second is the proper analysis of the FMR line shape, which remains the "Achilles heel" in interpreting experimental results, especially for either studying the spin pumping effect or quantifying the spin Hall angles via the electrically detected FMR.

We reveal the cooperative effect of coherent and dissipative magnon-photon couplings in an open cavity magnonic system, which leads to nonreciprocity with a considerably large isolation ratio and flexible controllability. Furthermore, we discover unidirectional invisibility for microwave propagation, which appears at the zero-damping condition for hybrid magnon-photon modes. A simple model is developed to capture the generic physics of the interference between coherent and dissipative couplings, which accurately reproduces the observations over a broad range of parameters. This general scheme could inspire methods to achieve nonreciprocity in other systems. Γ ZDC ω m ω c J Γe iπ ω c ω m J Γ ω m ω c Γe iπ ZDC ω m ω c J J ω m = ω c + 2JΓ α