Search

Coupling-induced transparency (CIT) and absorption (CIA) of transmission signals were experimentally observed in a single planar hybrid structure specially designed to consist of a yttrium iron garnet film and three concentric inverted-split-ring resonators (ISRRs). The observation of both CIT and CIA was ascribed to the cooperative effect of the interaction of magnons with three decoupled ISRRs' photon modes and the traveling waves along the microstripline. An analytical model developed based on the balance between the coherent and dissipative multiple-paths interactions precisely reproduced both CIT and CIA experimentally observed from a single hybrid system. This work, promisingly, can provide guidance for the design of efficient, flexible, and well-controllable magnon–photon hybrid devices that are highly in demand for applications to quantum technologies currently under development.

We studied the broadband characteristics of photon–magnon coupling (PMC) between a yuttrium iron garnet (YIG) film and arrays of inverted split-ring resonators (ISRRs). To achieve photon–magnon interaction available in a wide frequency range, we optimized the geometries and dimensions of single ISRRs and their array structure by numerical simulations in order to manipulate the resonance frequencies, bandwidths, and signal gains. With those optimal ISRRs arrays, we then experimentally observed multiples of anti-crossing regions between the YIG's magnon mode and the coupled photon modes from |S21|-vs-frequency measurements under different strengths of externally applied static magnetic fields. It was found that the bandwidth of photon–magnon interaction increases up to Δƒ ∼ 2 GHz for the number of ISRRs with N = 4. On the basis of an electromagnetic classical model, we analytically derived coupling between a photon's multiple resonance modes and the magnon mode in broad-range frequencies, the data on which is in good agreement with the experimental observation of the anti-crossing dispersions of the ISRR–array–YIG hybrid. This robust hybrid system provides for more reliable control not only of multiples of photon and magnon couplings in a wide range of operating frequencies but also of the net coupling strength variable in the 30–90 MHz range at room temperature. This experimental finding reveals the potential for development of a new class of wideband resonators and offers guidelines for the optimal design of planar-geometry, broadband photon–magnon devices.

The annealing effect of Pt/Permalloy(Py: Ni80Fe20)/Pt sandwich trilayer films on Gilbert damping was investigated through ferromagnetic resonance, x-ray diffraction (XRD), and transmission electron microscopy (TEM) measurements. We estimated the variation of the effective Gilbert damping constant with 30-min-post-annealing temperature in the range of Ta = 600–800 K. The damping constant for the as-grown sample was estimated to be αeff = 0.021, but it linearly increased with Ta until 700 K and then drastically increased by 4.5 times up to αeff = 0.093 at Ta = 800 K. Delicate analyses of the XRD and TEM data revealed that the damping constant in such a thin-layered structure is closely related to the structural characteristics of the interfaces and atomic intermixing through them. The linear increase in αeff in the range of Ta = 650–700 K was ascribed to the alloying/intermixing effect between the Pt and Py layers through both interfaces, whose effect was found to be related to the degradation of the Pt (111) texture. Meanwhile, in the range of Ta = 750–800 K, αeff further and rapidly increased relative to the values in the range of Ta = 650–700 K. Specifically, the 800-K-post-annealed sample showed that its damping constant was 4.5 times larger than that of the as-grown sample, its saturation magnetization decreased by ∼54%, and also that new stoichiometric compounds such as NiPt, FePt, and NiFePt appeared. TEM equipped with energy-dispersive x-ray spectroscopy also revealed that Ta gives rise to atomic intermixing between the Pt and Py thin layers through both interfaces, resulting in interface shifting. This work provides the means to control the Gilbert damping constant and better to understand complex multi-layered structures in potential spintronic devices.

We studied “strongly enhanced” excitations of magnetostatic spin-waves in a hybrid magnon-photon-coupled system consisting of an inverted split-ring resonator and an yttrium iron garnet film. The backward-volume magnetostatic wave, magnetostatic surface wave, forward-volume magnetostatic wave modes, as well as multiple mixed modes were observed according to the direction of externally applied magnetic fields with respect to the spin-wave propagation direction. From experimental measurements, we found that there exist certain characteristic angles, which is to say, critical angles (θc, ϕc), whereby the group velocity of the excited spin-wave modes reaches zero, along with a single ferromagnetic resonance peak. Furthermore, we analytically derived the critical angles as sin θ c = ( H eff / H ) { 2 − ( 1 + μ 0 M s / H eff ) si n 2 ϕ c } − 1 / 2 , where Heff is the effective magnetic-field strength, H the externally applied field strength, and μ0Ms is the saturation magnetization. This analytical form is in quantitative agreement with estimations from experimentally observed spin-wave modes. This work not only provides a better understanding of multiple-mode spin-wave excitations in given field directions with the help of photon-magnon coupling, but also offers better coupling controllability based on the change of the external magnetic field direction.

Yttrium iron garnet (YIG:Y3Fe5O12) thin films were grown on (111) gadolinium gallium garnet (Gd3Ga5O12, GGG) substrates using pulsed-laser deposition under several different deposition and annealing conditions. X-ray diffraction measurements revealed that the crystallographical orientation of the YIG films is pseudomorphic to and the same as that of the GGG substrate, with a slight rhombohedral distortion along the surface normal. Furthermore, X-ray reciprocal space mapping evidenced that in-situ annealed YIG films during film growth are under compressive strain, whereas ex-situ annealed films have two different regions under compressive and tensile strain. The saturation magnetization ( 4 π M S) of the films was found to vary, according to the deposition conditions, within the range of 1350 to 1740 G, with a very low coercivity of H C

By using the stripline Microwave Vector Network Analyzer Ferromagnetic Resonance and Pulsed Inductive Microwave Magnetometry spectroscopy techniques, we study a strong coupling regime of magnons to microwave photons in the planar geometry of a lithographically formed split-ring resonator (SRR) loaded by a single-crystal epitaxial yttrium-iron garnet (YIG) film. Strong anti-crossing of the photon modes of SRR and of the magnon modes of the YIG film is observed in the applied-magnetic-field resolved measurements. The coupling strength extracted from the experimental data reaches 9 percent at 3 GHz. Theoretically, we propose an equivalent circuit model of an SRR loaded by a magnetic film. This model follows from the results of our numerical simulations of the microwave field structure of the SRR and of the magnetization dynamics in the YIG film driven by the microwave currents in the SRR. The equivalent circuit model is in good agreement with the experiment. It provides a simple physical explanation of the process of mode anti-crossing. Our findings are important for future applications in microwave quantum photonic devices as well as in magnetically tunable metamaterials exploiting the strong coupling of magnons to microwave photons.