Study of the negative magnetization phenomenon in NBu4[FeIIFeIII(ox)3]

Temperature and magnetic field dependent magnetization studies of ferrimagnetic NBu4[(FeFeIII)-Fe-II(ox)(3)] are presented, which demonstrate that the negative magnetization phenomenon in the field-cooled mode, observed only in magnetic fields lower than 5 kOe and at temperatures below 30 K. The absolute value of the ferrimagnetic saturation magnetization is 0.07 mu(B), estimated from the field dependence of the held-cooled magnetization at 5 K, which is only the 7% of the theoretically expected value at 0 K. A magnetic field dependence of the compensation temperature as well as a temperature dependence of compensating magnetic field are observed. The hysteresis curve at 5 K under field-cooled mode under 1 kOe magnetic field shows a negative center off-set indicating the presence of large anisotropy in the material at low temperatures. The memory of the field-cooling procedure cannot be destroyed by a magnetic field of 55 kOe.