Ag:Er alloy having paramagnetic properties were synthesized for temperature sensors of metallicmagnetic calorimeters. The Ag:Er master alloy and the 2-inch target for film deposition were manufacturedusing vacuum arc melting and RF heating methods, respectively, under process conditions designed to min-imize impurity contamination. Calculations and measurements of magnetization versus magnetic field wereemployed to check magnetic impurities in host material, Ag, and to estimate the Er concentration in Ag:Eralloys at each steps of synthesis. The temperature-dependent magnetization of the thin films deposited fromsynthesized Ag:Er with 168Er isotope was measured in mK range, demonstrating their suitability as tempera-ture sensor for low-temperature detectors such as MMCs