Diamond magnetometer enhanced by ferrite flux concentrators

Abstract

Magnetometers based on nitrogen-vacancy (NV) centers in diamond are promising room-temperature, solidstate sensors. However, their reported sensitivity to magnetic fields at low frequencies (1 kHz) is presently 10 pT s 1/2 , precluding potential applications in medical imaging, geoscience, and navigation. Here we show that high-permeability magnetic flux concentrators, which collect magnetic flux from a larger area and concentrate it into the diamond sensor, can be used to improve the sensitivity of diamond magnetometers. By inserting an NV-doped diamond membrane between two ferrite cones in a bowtie configuration, we realize a ∼250-fold increase of the magnetic field amplitude within the diamond. We demonstrate a sensitivity of ∼0.9 pT s 1/2 to magnetic fields in the frequency range between 10 and 1000 Hz. This is accomplished using a dual-resonance modulation technique to suppress the effect of thermal shifts of the NV spin levels. The magnetometer uses 200 mW of laser power and 20 mW of microwave power. This work introduces a new degree of freedom for the design of diamond sensors by using structured magnetic materials to manipulate magnetic fields.

Integrated and Portable Magnetometer Based on Nitrogen‐Vacancy Ensembles in Diamond

“…R shunt ⋅e results in ≈ 2.47 × 10 14 Hz with e being the elementary charge. Using Equation (2) and the measured linewidth of 92.19 kHz and contrast of 0.62 % the photon shot-noise limited sensitivity is ≈ 26 pT Hz −1/2 .…”

“…Besides the implementation of temperature invariance of the NV sensor, another possibility to enhance the achievable sensitivity could be the use of flux concentrators, as recently shown by Fescenko et al., which collect the magnetic flux from a large area and direct it to the NV sensor. [ 14 ] The use of such concentrators must nevertheless be viewed critically from the point of view of the intended application, as any restrictions on the use of the sensor could be associated with the use of these concentrators, e.g., for a vector magnetometry application.…”

“…[27] The following analysis will refer to f c . For an enhancement of the magnetic sensitivity we simultaneously applied three mean frequencies f c , f c − f HFS , and f c + f HFS in order to address all three 14 N hyperfine resonances with a frequency splitting f HFS of 2.16 MHz simultaneously. [19,28] In the following, we will label such measurements with "3 HFS on", while "3 HFS off" means that only the mean frequency f c is applied.…”

Optimization of a Diamond Nitrogen Vacancy Centre Magnetometer for Sensing of Biological Signals

“…A number of novel sensing techniques are currently being pursued which are suitable for sensing in this low frequency regime. This includes experiments using an optical cavity and infrared or green absorption [41,42] or the very recent work by Fescenko et al [43] promising sub-pT/ √ Hz sensitivity using flux concentrators. Novel techniques at an early stage, such as laser threshold magnetometry [44,45] also appear promising.…”

Gradiometer Using Separated Diamond Quantum Magnetometers

“…For a system of applications, compact integrated magnetometers using the NV center demonstrated the minimal detectable magnetic field of sub−10 nT/√Hz sensitivity over a 125 Hz bandwidth using a balanced detection method [ 12 ] and 1 μT in 1 ms integration time with the specific construction volume of about 2.9 cm 3 [ 13 ]. For the sensitivity improvements, the magnetic sensitivity of 0.9 pT/√Hz was achieved for an AC magnetic signal at 20 kHz [ 14 ] and magnetic signals in the frequency range between 10 Hz and 1 kHz [ 15 ]. As a result of these epoch-making demonstrations of magnetometry using the NV center, magnetoencephalography (MEG) [ 16 ], which requires highly sensitive magnetic sensors, is now one of the most challenging target applications using the NV center.…”