Broadband multi-magnon relaxometry using a quantum spin sensor for high frequency ferromagnetic dynamics sensing.

Development of sensitive local probes of magnon dynamics is essential to further understand the physical processes that govern magnon generation, propagation, scattering, and relaxation. Quantum spin sensors like the NV center in diamond have long spin lifetimes and their relaxation can be used to sense magnetic field noise at gigahertz frequencies. Thus far, NV sensing of ferromagnetic dynamics has been constrained to the case where the NV spin is resonant with a magnon mode in the sample meaning that the NV frequency provides an upper bound to detection. In this work we demonstrate ensemble NV detection of spinwaves generated via a nonlinear instability process where spinwaves of nonzero wavevector are parametrically driven by a high amplitude microwave field. NV relaxation caused by these driven spinwaves can be divided into two regimes; one- and multi-magnon NV relaxometry. In the one-magnon NV relaxometry regime the driven spinwave frequency is below the NV frequencies. The driven spinwave undergoes four-magnon scattering resulting in an increase in the population of magnons which are frequency matched to the NVs. The dipole magnetic fields of the NV-resonant magnons couple to and relax nearby NV spins. The amplitude of the NV relaxation increases with the wavevector of the driven spinwave mode which we are able to vary up to 3 × 106 m-1, well into the part of the spinwave spectrum dominated by the exchange interaction. Increasing the strength of the applied magnetic field brings all spinwave modes to higher frequencies than the NV frequencies. We find that the NVs are relaxed by the driven spinwave instability despite the absence of any individual NV-resonant magnons, suggesting that multiple magnons participate in creating magnetic field noise below the ferromagnetic gap frequency which causes NV spin relaxation.

Simple Hamiltonian approach to describe large-amplitude and higher-order parametric resonances.

Parametric resonance is a complex phenomenon that touches many aspects of scientific and technical society, but is still not well understood because of the intensive calculations required to describe the behavior. Thus the importance of developing simple mathematical approaches to describe parametric resonance cannot be overstated. Here a consistent theory of the parametric resonance of a harmonic oscillator under any periodic frequency modulation is constructed. Using a Hamiltonian approach and resonance approximation, simple equations were derived and critical amplitudes for all parametric resonance orders were obtained for any periodic modulation function. The theory agrees with the well-known result for the main resonance and gives correct power dependence on damping. In addition, the theory qualitatively predicts behavior at large modulations. This simplified approach revealed unique features-"safety windows" at large modulation amplitudes where parametric resonance does not occur which were then qualitatively confirmed with numerical simulations. The Hamiltonian approach should serve as a framework that a greater understanding of parametric resonance at large amplitudes and higher orders can be built upon.

Supplementation with hydrogen-producing composition confers beneficial effects on physiology and life span in Drosophila.

Recently, molecular hydrogen (H2) has become known as a new class of antioxidants and redox-modulating interventions. Effects of H2 have been documented for many acute and chronic pathological conditions. The present study was aimed at determining the effect of hydrogen on the physiology and longevity of Drosophila. The flies were given a patented food supplement consisting of a mixture of inert salts with metallic magnesium, which reacted with acidic aqueous solutions, thereby releasing hydrogen gas. The supplementation with hydrogen-rich food prolonged the life span of the wild-type strain. To gain insights into the effect of hydrogen, we used previously generated mutant under-expressing redox-regulating enzymes, peroxiredoxins, in mitochondria. The hydrogen-releasing material lessened the severe shortening of life span of the mutant. Hydrogen also delayed the development of intestinal dysfunction caused by under-expression of peroxiredoxins in the intestinal epithelium. Hydrogen also averted a significant decrease in the mobility of mutant flies that under-expressed peroxiredoxins globally or in specific tissues. Together, the results showed that the introduction of hydrogen to aging or short-lived flies could increase their survival, delay the development of the intestinal barrier dysfunction and significantly improve physical activity.