Temperature dependence of antiferromagnetic susceptibility in ferritin.

We show that antiferromagnetic susceptibility in ferritin increases with temperature between 4.2 and 180 K (i.e., below the Neel temperature) when taken as the derivative of the magnetization at high fields (30×10(4) Oe). This behavior contrasts with the decrease in temperature previously found, where the susceptibility was determined at lower fields (5×10(4) Oe). At high fields (up to 50×10(4) Oe) the temperature dependence of the antiferromagnetic susceptibility in ferritin nanoparticles approaches the normal behavior of bulk antiferromagnets and nanoparticles considering superantiferromagnetism, this latter leading to a better agreement at high field and low temperature. The contrast with the previous results is due to the insufficient field range used (< 5x10(4) Oe), not enough to saturate the ferritin uncompensated moment.