  Many animal species were verified to use geomagnetic field for their
navigation, but the biophysical mechanism of magnetoreception has remained
enigmatic. This paper presents a special biophysical model that consists of
magnetite-based and radical-pair-based mechanisms for avian magnetoreception.
The amplitude of the resultant magnetic field around the magnetic particles
corresponds to the geomagnetic field direction and affects the yield of
singlet/triplet state products in the radical-pair reactions. Therefore, in the
proposed model, the singlet/triplet state product yields are related to the
geomagnetic field information for orientational detection. The resultant
magnetic fields corresponding to two materials with different magnetic
properties were analyzed under different geomagnetic field directions. The
results showed that ferromagnetic particles in organisms can provide more
significant changes in singlet state products than superparamagnetic particles,
and the period of variation for the singlet state products with an included
angle in the geomagnetic field is approximately 180{\deg} when the magnetic
particles are ferromagnetic materials, consistent with the experimental results
obtained from avian magnetic compass. Further, the calculated results of the
singlet state products in a reception plane showed that the proposed model can
explain the avian magnetoreception mechanism with an inclination compass.
