Effects of pressure on magnetic properties of ferrihydrite antiferromagnetic nanoparticles

The effects of pressure on iron oxide hydroxide ferrihydrite (FeOOH∣nH₂O) nanoparticles with particle size of 4.7 ± 0.2 nm were investigated through DC magnetic measurements in the pressure region up to P = 13.5 kbar. The magnetization curve up to 50 kOe exhibits the coexistence of saturation and linear contributions. The value of high field susceptibility, the latter contribution, increases with increasing pressure for P ≤ 10.0 kbar. In contrast, the former contribution, associated to the uncompensated moment, decreases for P ≤ 10.0 kbar. At further pressure, there is no distinct pressure response. These effects of pressure are probably related to changes in the anisotropy energy due to the volume shrinkage.