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.

开发灵敏的磁振动力学局部探针对于进一步了解控制磁振子产生，传播，散射和弛豫的物理过程至关重要。像钻石中的NV中心这样的量子自旋传感器具有很长的自旋寿命，其弛豫可用于感测千兆赫兹频率的磁场噪声。到目前为止，铁磁动力学的NV感应已被限制为NV NV自旋在样品中以磁振子模式共振的情况，这意味着NV频率为检测提供了上限。在这项工作中，我们展示了通过非线性不稳定性过程生成的自旋波的整体NV检测，其中非零波矢的自旋波由高振幅微波场参数化驱动。由这些驱动的自旋波引起的NV弛豫可以分为两种情况：一磁和多磁non NV弛豫法。在单磁振NV弛豫法中，驱动的自旋波频率低于NV频率。被驱动的自旋波经历四磁振子散射，导致与NV频率匹配的磁振子数量增加。NV共振磁振子的偶极磁场耦合到附近的NV自旋并使其松弛。NV弛豫的幅度随驱动自旋波模式的波矢增加而增大，我们最多可以改变3×10 NV共振磁振子的偶极磁场耦合到附近的NV自旋并使其松弛。NV弛豫的幅度随驱动自旋波模式的波矢增加而增大，我们最多可以改变3×10 NV共振磁振子的偶极磁场耦合到附近的NV自旋并使其松弛。NV弛豫的幅度随驱动自旋波模式的波矢增加而增大，我们最多可以改变3×10⁶  m ^-1，进入自旋波谱中由交换相互作用主导的部分。增加施加磁场的强度会使所有自旋波模式的频率都高于NV频率。我们发现，尽管没有任何单个的NV共振磁振子，但NVs被驱动的自旋波不稳定性所放松，这表明多个磁振子参与产生低于铁磁隙频率的磁场噪声，从而导致NV旋转弛豫。