  Magnetic measurement can be performed by various sensors, such as SQUID and
Giant Magnetoresistance. This device can achieve high accuracy while losing
efficiency and convenience. The model of biological magnetic sensing in avian
proposes a radical pair response to the external field on the FLY results in
regulating animal behaviour. Inspired by the radical pair system found in
biological system, the effect of intra-radical coupling and the initial
condition is studied in this simplified radical pair model as the quantum
advantage results from entanglement and superposition are investigated in
metrology. To identify the sensing benefit from the cooperation between the
radical pairs, the inter-radical coupling is considered. We find the
intra-radical coupling determines the sensing regime while the coupled radical
pair system enables a new sensing scheme that provides a more general and
flexible way for magnetic sensing in a broader range through a easier
manipulation to the system.
