Development of Metallic Magnetic Calorimeters with a Critical Temperature Switch

Abstract

We report on the progress in the development of meander-shaped metallic magnetic calorimeters (MMCs) with a critical temperature switch. A niobium meander-shaped coil in an MMC is arranged to form a superconducting loop. It is to measure the change in magnetization and to apply a persistent current that magnetizes the MMC sensor material. In this work, part of the superconducting loop is fabricated with another superconducting material with its transition temperature ( $$T_\mathrm{C}$$ ) lower than that of niobium. A persistent current can be injected in the loop while reducing the temperature from above to below the $$T_\mathrm{C}$$ of the switch. Aluminum (Al) wires and an alloy of molybdenum and germanium (MoGe) were tested as critical temperature switch. The test with the Al switch demonstrated the temperature switch concept for meander-shaped MMCs that require a large field current. Microfabricated MoGe switches showed a $$T_\mathrm{C}$$ near 4.3 K, but only 7 mA of persistent current could be charged due to MoGe film discontinuity. This issue requires further improvement in the fabrication procedure.