Negative remanence in magnetic nanostructures

In nearly percolating magnetic granular (Ni,Fe)-SiO2 films, we observed negative remanence, or a negative remanent magnetization, upon removing the positively applied magnetic field to zero. We propose that there exist both superparamagnetic and ferromagnetic components due to different connectivity of magnetic nanometer scaled particles, as supported by the dark field transmission electron microscopy images. The magnetostatic interaction between them favors an opposite alignment. Moreover, the two-component hypothesis explains satisfactorily the dependencies of the negative remanence on temperature and magnetic volume fraction. (C) 1996 American Institute of Physics.