We present an exhaustive theoretical analysis of charge and thermoelectric transport in a normal-metal–ferromagnetic-insulator–superconductor junction and explore the possibility of its use as a sensitive thermometer. We investigate the transfer functions and the intrinsic noise performance for different measurement configurations. A common feature of all configurations is that the best temperature-noise performance is obtained in the nonlinear temperature regime for a structure based on an Europium chalcogenide ferromagnetic insulator in contact with a superconducting Al film structure. For an open-circuit configuration, although the maximal intrinsic temperature sensitivity can achieve $10\mathrm{nK}{\mathrm{Hz}}^{-1/2}$, a realistic amplifying chain will reduce the sensitivity up to $10\mu \mathrm{K}{\mathrm{Hz}}^{-1/2}$. To overcome this limitation, we propose a measurement scheme in a closed-circuit configuration based on state-of-the-art superconducting-quantum-interference-device detection technology in an inductive setup. In such a case, we show that temperature-noise can be as low as $35\mathrm{nK}{\mathrm{Hz}}^{-1/2}$. We also discuss a temperature-to-frequency converter where the obtained thermovoltage developed over a Josephson junction operated in the dissipative regime is converted into a high-frequency signal. We predict that the structure can generate frequencies up to approximately 120 GHz and transfer functions up to $200\mathrm{GHz}/\mathrm{K}$ at around 1 K. If operated as an electron thermometer, the device may provide temperature-noise lower than $35\mathrm{nK}{\mathrm{Hz}}^{-1/2}$ thereby being potentially attractive for radiation-sensing applications.

• Received 4 June 2015

DOI:https://doi.org/10.1103/PhysRevApplied.4.044016