Characterization of Magnetic Sensors for MAGNETO Dark Matter Search Experiments

The MAGNETO-χ experiment will search for sub-GeV dark matter using diamond/sapphire crystals and magnetic quantum sensors. Athermal phonons produced by dark matter scattering in the crystals are measured by magnetic quantum sensors capable of sub-microsecond timing resolution. This capability enables enhanced phonon pulse shape discrimination for active rejection of electron-recoil background and low energy noise. Magnetic quantum sensors utilize paramagnetic materials for phonon sensing and SQUID (Superconducting Quantum Interference Device) magnetometers for measurement of resulting magnetic flux changes. Au:Er paramagnetic alloy materials are synthesized, tested, and characterized for the MAGNETO-χ experiment. Cryogenic magnetic responses at millikelvin temperatures, response speed of the sensors, and magnetic coupling between the sensor and SQUID are demonstrated.