Observation of ferromagnetic clusters in Bi_0.125Ca _0.875MnO₃

The electron doped manganite system, Bi_0.125Ca _0.875MnO₃, exhibits large bulk magnetization of unknown origin. To select amongst possible magnetic ordering models, we have conducted temperature and magnetic field dependent small-angle neutron scattering measurements. Non-trivial spin structure has been revealed. Ferromagnetic spin clusters form in the antiferromagnetic background when temperature is decreased to T_c∼108K. With a further reduction in temperature or the application of external magnetic field, the clusters begin to form in larger numbers, which gives an overall enhancement of magnetization below T _c.