The sensitivity of magnetic calorimeters with large heat capacity

Magnetic sensors, based on the measurement of the magnetization of paramagnetic spins, possess characteristics that make them suitable for use with low-temperature calorimeters having large heat capacities. When the properties of the sensor, which can be calculated, are optimized for a given heat capacity, the energy resolution depends on heat capacity roughly as C1/3. We have obtained an energy resolution of 135 eV at 6 keV with a calorimeter having a heat capacity of 4×10−9 J/K. No deviations from a linear response with respect to energy were observed in the detector up to 136 keV. Prospects for the improvement of the performance of large calorimeters are discussed.