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 (30x10(4) Oe). This behavior contrasts with the decrease in temperature previously found, where the susceptibility was determined at lower fields (5x10(4) Oe). At high fields (up to 50x10(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.