Demagnetizing Field Induced Instability in a Superferromagnetic (CoFe2O4)20 Ag80 Nanocomposite

The magnetic properties of a (CoFe2O4)20Ag80nanocomposite packed into a cylindrical sample holder were investigated. The nanoparticle system becomes superferromagnetic (SFM) below 223 K. The SFM state was investigated by measuring the temperature dependence of the zero-field-cooled (ZFC) and field-cooled (FC) magnetizations and by recording hysteresis loops. For magnetic field (H) applied along the axis of the sample holder, the ZFC and FC magnetizations and the hysteresis loops showed typical behaviors of a SFM phase yielding a remanence of 49.2 emu/cm3and a coercivity of 9.65 kOe at 10 K. The demagnetizing field for H applied transverse to the axis of the sample holder induced an instability that reduced the magnitude of the remanence to 12.7 emu/cm3and reduced the coercivity to 31 Oe at 10 K. The overall results are explained in terms of macroscopic demagnetizing fields.