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

Abstract

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.

Quantum Engineering With Hybrid Magnonic Systems and Materials (Invited Paper)

“…In this section, we review the recent progress of NV center based quantum sensing platform and its application to detect magnons in functional spintronic systems. Due to their single-spin sensitivity, NV centers have been demonstrated to be a powerful sensing tool to detect magnetic domains, [226][227][228][229] spin transport, 9 and dynamic behaviors [230][231][232][233] in a range of emergent magnetic materials. A unique advantage of NV centers results from a combination of the high field sensitivity and nanoscale spatial resolution.…”

Imaging non-collinear antiferromagnetic textures via single spin relaxometry

“…Magnetic noise with a spectral component resonant with the electron spin transition of the NV defect is usually detected by recording variations of its longitudinal spin relaxation time T 1 17 . This method, commonly referred to as relaxometry 18 , has been used for various purposes in the past years, including the study of Johnson noise in metals 19 , 20 , current fluctuations in graphene devices 21 , paramagnetic nanoparticles 22 – 24 and spin waves in ferromagnets 25 – 27 . In contrast to these previous works, we introduce a relaxometry-based imaging mode, which relies on the simple measurements of the photoluminescence (PL) signal of the NV defect under continuous laser illumination.…”

Noninvasive measurements of spin transport properties of an antiferromagnetic insulator

“…Such magnetic noise can be understood by invoking the Holstein-Primakoff transformation: s ⊥ ∝α + (α), s ∥ ∝ s − α + α, with α + (α) being the magnon creation (annihilation) operator ( 37 ). In an intuitive picture, the transverse spin noise δ B ⊥ ( t ) is related to one-magnon scattering processes ( 34 , 38 , 39 ), i.e., the creation or annihilation of magnons, which vanish at frequencies below the magnon band minimum. The longitudinal spin noise δ B ∥ ( t ) is related to two-magnon scattering processes, where a magnon with frequency f + f 2m can undergo a transition to another magnon with frequency f (or vice versa), emitting magnetic noise at frequency f 2m as illustrated in Fig.…”