We have investigated the magnetotransport and noise properties of magnetic tunnel junctions incorporating a superparamagnetic free layer, in a wide temperature range from 150 K to 400 K. Both 1/f noise and sensitivity reach the maximum near the blocking temperature of the superparamagnetic transition. The smooth change of noise around the blocking temperature is attributed to size distribution of nanoclusters comprising the free layer. The best detectability (40nT/Hz at 1 Hz) is achieved at 350 K. In ferromagnetic and superparamagnetic states, 1/f noise follows different scaling relations with respect to sensitivity. The change of scaling law is explained by thermodynamics of the nanoclusters.

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