By using the stripline Microwave Vector-Network Analyser 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% at 3 GHz.Theoretically, we propose an equivalent circuit model of the 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 magnetisation 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 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 nonlinear and magnetically tuneable metamaterials exploiting the strong coupling of magnons to microwave photons.

Zinc ferrite films were deposited on fused quartz substrate at different temperatures using pulsed laser ablation (PLA) and rf sputtering. X-ray diffraction indicated that all the films were single phase ZnFe2O4 with grain growing in the range of 8–80nm with substrate temperature. The nanocrystalline films were found to be magnetic and the spontaneous magnetization showed a strong dependence on the grain size, dropping sharply for films with larger grains. A PLA thin film deposited in vacuum at 500°C exhibited a room temperature magnetization value of 5560G.

The sputter deposited NiZn ferrite thin films were studied as a function of annealing temperature. The magnetization showed a monotonic increase with increasing annealing temperature. The coercivity shows a minimum at annealing temperature of 400 °C and shows a value of 14 Oe. Transmission electron microscopy study indicated that the grain size increases from ∼3 nm for the as-deposited case to ∼15 nm for the film annealed at 800 °C. The observed coercivity behavior could be attributed to the defects present in the films, the change in cation distribution, and the grain growth.

Direct detection of magnon spin transport by the inverse spin Hall effect Appl. Phys. Lett. 100, 082405 (2012) Ferromagnetic resonance of micro-and nano-sized hexagonal ferrite powders at millimeter waves J. Appl. Phys. 111, 07E113 (2012) Tuning the cation distribution and magnetic properties of single phase nanocrystalline Dy3Fe5O12 garnet J. Appl. Phys. 111, 07A517 (2012) Evolution of crystallographic texture and magnetic properties of polycrystalline barium ferrite thick films with Bi2O3 additive J. Appl. Phys. 111, 07A511 (2012) Field-induced magnetic transition in cobalt-ferrite J. Appl. Phys. 111, 07E308 (2012) Additional information on J. Appl. Phys. with xϭ0.32 were rf sputter deposited on fused quartz substrates at ambient temperature. The as-deposited films were found by x-ray diffraction to be amorphous but magnetic, and showed large high field susceptibility. The films were studied after they were annealed at various temperatures up to 850°C. It was observed that the films crystallize upon annealing and the value of the saturation magnetization increases with annealing temperature. The high field susceptibility, on the other hand, decreases with increasing anneal temperature. The measured ferromagnetic resonance spectra of these films indicated that the films consist of at least two different magnetic materials. A significant portion in the film crystallizes and the value of saturation magnetization of this portion tends to the bulk value as annealing temperature is increased. However, a small portion of the film remains in a highly defective state all through, even up to annealing temperatures of 850°C. The high field susceptibility data indicates that point defects could play an important role in determining the magnetic properties of these films.

Copper ferrite (CuFe 2 O 4) thin films have been prepared by rf sputtering on fused quartz and silicon ͑111͒ substrates at ambient temperature. The as-deposited film is found to be in cubic phase, which is stable only at higher temperatures in bulk. The films were annealed at temperatures ranging from 100°C to 800°C and slowly cooled. The films had tetragonal structure at annealing temperature above 200°C. The c/a ratio was observed to increase with increasing annealing temperature. Transmission electron microscopy study confirmed the phase transformation from cubic to tetragonal as a function of annealing temperature. The magnetization values of the films were observed to show a maximum at the annealing temperature of 200°C and a minimum at 500°C. The coercivity increased monotonically from 70 Oe for the as-deposited film, to 1450 Oe for the film annealed at 800°C. The results were explained on the basis of the phase transformation and the grain growth phenomenon.