Magnetic calorimeters for high resolution x-ray spectroscopy

Microcalorimeters operating at low temperatures have proven to be suitable tools for high resolution x-ray spectroscopy. Metallic magnetic calorimeters (MMCs) are one kind of such detectors. The operation of a MMC is based on the temperature dependence of the magnetization of a paramagnetic material such as Au doped with Er in a small magnetic field. The temperature of a x-ray absorber, in thermal contact with the paramagnetic material, can be monitored with high sensitivity by using a dc superconducting quantum interference device. An energy resolution of one part in 1000 at 6 keV has now been demonstrated for MMCs. We report on the recent progress in the development of MMCs and discuss the limitations of such devices resulting from fundamental noise sources