This thesis describes the development of a metallic metallic calorimeters (MMC) for a soft x-ray detection. A MMC utilize diluted concentration of a paramagnetic material in a non-magnetic metal host as a temperature sensor. The sensor is placed in a weak field and operated typically below 100 mK. The temperature rise on absorption of a particle leads to a change of the magnetization of the sensor material, which is read out by a dc SQUID magnetometer. A field of application for a MMC is x-ray astronomy as a focal plane detector for imaging and high energy resolution spectroscopy. Thin film technology is suitable to fabricate such detector arrays. Thin films of erbium diluted in gold (Au:Er) were dc magnetron sputter-deposited using Au:Er alloy targets under different conditions, and the magnetic properties of the films have been studied. The magnetization of the film agreed with that of the target material from room temperature down to 200 mK, however, the magnetization of the film showed an enhanced exchange interaction among Er ions below 200 mK. The possible origin of the interaction is discussed. Au:Er films were deposited on flux transformer chips of four pixel MMC arrays. Meander pick-up coils for each pixel also provide a magnetic field by applying a superconducting persistent current. The test results of the prototype detector arrays are presented. X-ray signals of 55Fe source are analyzed.
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