Development of metallic magnetic calorimeters for high-resolution X-ray spectroscopy

X-ray detectors based on the concept of magnetic calorimetry are well suited for high-resolution spectroscopy. Metallic magnetic calorimeters (MMC) make use of a metallic paramagnetic temperature sensor, gold doped with few hundred ppm erbium, which is in tight thermal contact with a metallic absorber. The sensor is placed in a weak magnetic field, its magnetization is used to monitor the temperature. High-energy resolution can be obtained by using a low-noise, high-bandwidth DC SQUID to measure the small change in magnetization upon the absorption of an X-ray. In many applications it is important to have a detector that has a high stopping power for photons up to 10 keV and allows to measure with a high count rate. The design of the detector we present is based on a numerical calculation that gives the optimal values for sensor size, erbium concentration and applied magnetic field. The detector has a stopping power of about 98% at 6 keV and the decay time has been improved by a better thermal link between the sensor and the thermal bath. The energy resolution we achieved is ΔEFWHM=2.7 eV for X-ray energies up to 6.5 keV. (orig.)