Spinwave detection by nitrogen-vacancy centers in diamond as a function of probe–sample separation

Abstract

Magnetic field noise from magnons can reduce the lifetimes of proximate spins and degrade the performance of spin based technologies. However, spatial and temporal averaging over the area of typical field sensors makes measuring magnetic field noise challenging. Here, we use an ensemble of nitrogen-vacancy (NV) point-defects in diamond to measure the spectral profile of thermally excited spinwave noise at room temperature as a function of the distance away from a 20 nm thick Permalloy (Py) thin film. We systematically vary the separation between the NV and Py layers using a silicon-dioxide wedge and measure the longitudinal relaxation rate of the NV center ms = 0 state as a function of the separation. The measured spinwave-induced relaxation of an ensemble of NV centers is well described by a magnetostatic model of dipole fields from the spinwaves. We furthermore find that our all-optical, nonperturbative measurements of the spinwave noise can be used to extract information about the ferromagnetic source, such as magnetization, damping, and fluctuating amplitude. This technique is amenable to application with stand-off from ferromagnetic elements and from buried structures.

Frequency multiplication by collective nano-scale spin wave dynamics

“…At first glance these may be characterized as follows: (I) a continuous resonance at and below the ferromagnetic resonance (FMR) field, (II) a strong enhancement at 2/3 of the NV centers resonance frequency and (III) a series of resonance lines at low bias fields. The occurrence of the FMR in the ODMR signal (I) has been observed before [30-33, 42, 43] and the effect is attributed to dipolar stray fields generated by spin waves acting on the NV centers [31]. Feature (II) occurs at a frequency of 2/3 f ESR , i.e., at 1.9 GHz.…”

“…In this article, we explore the non-linear response of a soft ferromagnet close to zero magnetic field at large driving amplitudes and small frequencies. Spin waves are probed using diamond Nitrogen vacancy (NV) center nanoscale magnetometry [28][29][30][31][32][33][34] and time-resolved magneto optic Kerr microscopy (MOKE) [35][36][37]. In the measurements we indeed find evidence for the expected spin waves precessing at 3/2 of the driving frequency and -very surprisingly -a series of additional spin wave excitations precessing at up to the 60 th harmonic of the pumping frequency.…”

Sensing chiral magnetic noise via quantum impurity relaxometry

“…(3) and ( 6) reduce to the existing theoretical models used in Refs. [13,14,17]. Since such models neglect surface charges, the chiral nature of the magnon noise is neglected and we refer to them as the achiral theory.…”

“…Quantum impurity (QI) relaxometry [7,8]-a sensing scheme measuring the relaxation rate of an impurity spin due to its coupling with magnetic noise [9][10][11][12]-has recently emerged as a sensitive, local, and noninvasive technique for probing condensed-matter systems including magnetic materials [13][14][15][16][17][18][19][20][21]. QIs coupled to magnetic thin films form model systems for developing an understanding of decoherence introduced in qubits that are in close proximity to magnetic materials.…”

“…Consequently, the m s = 0 → −1 and m s = 0 → +1 transitions of a prototypical spin-1 QI are driven by magnon-generated fields of different magnitudes. Theoretical models used to analyze experiments [13,14,17] by excluding out-of-plane magnetization fluctuations (and thus σ m ) neglect the role of chirality and require arbitrary scale factors of unknown origin to quantitatively fit the experimentally measured relaxation rates for the m s = 0 → −1 and m s = 0 → +1 transitions.…”