  We present an exhaustive theoretical analysis of charge and thermoelectric
transport in a normal metal-ferromagnetic insulator-superconductor (NFIS)
junction, and explore the possibility of its use as a sensitive thermometer. We
investigated 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 non-linear
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 $10$nKHz$^{-1/2}$, a realistic amplifying chain will
reduce the sensitivity up to $10$$\mu$KHz$^{-1/2}$. To overcome this limitation
we propose a measurement scheme in a closed-circuit configuration based on
state-of-art SQUID detection technology in an inductive setup. In such a case
we show that temperature noise can be as low as $35$nKHz$^{-1/2}$. We also
discuss a temperature-to-frequency converter where the obtained thermo-voltage
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 $\sim 120$GHz, and transfer functions up to
$200$GHz/K at around $\sim 1$K. If operated as electron thermometer, the device
may provide temperature noise lower than $35$nKHz$^{-1/2}$ thereby being
potentially attractive for radiation sensing applications.
