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Smallest magnetoreceptor unit consisting of 10 maghemite platelets (boxes) and a magnetite cluster (sphere). The coordinate frame shown in the figure is used in the computations throughout the article. The direction of the external magnetic induction vector 
is characterized by the polar angle Θ and the azimuthal angle Φ as shown. The magnetic moments of the ith maghemite platelet and of the magnetite cluster are shown with 
and 
respectively.
