  Here I present the SiC-YiG Quantum Sensor, allowing electron paramagnetic
resonance (EPR) studies of monolayer or few nanometers thick chemical,
biological or physical samples located on the sensor surface. It contains two
parts, a 4H-SiC substrate with many paramagnetic silicon vacancies (V2) located
below its surface, and YIG ferrimagnetic nanostripes. Spins sensing properties
are based on optically detected double electron-electron spin resonance under
the strong magnetic field gradient of nanostripes. Here I describe fabrication,
magnetic, optical and spins sensing properties of this sensor. I show that the
target spins sensitivity is at least five orders of magnitude larger than the
one of standard X band EPR spectrometer, for which it constitutes, combined
with a fiber bundle, a powerful upgrade for sensitive surface EPR. This sensor
can determine the target spins planes EPR spectrum, their positions with a
nanoscale precision of +/- 1 nm, and their 2D concentration down to
1/(20nm.20nm).
