2D SANS pattern of F27 sample show intensity peaks around Q y ≈ ±0.02 Å −1 even at low field of 0.004 T ( Figure 3a ) . Increasing the magnitude of the applied magnetic field changes the 2D SANS pattern of F27 IONPs from curved and diffuse horizontal stripes at low fields into sharp straight stripes at high fields ( Figure 3a - f ) . Importantly , the field - induced patterns revert back to their original state by removing the magnetic field . The radially averaged data shown in Figure 2 indicates the presence of chains , thus 2D anisotropic SANS data is divided into sectors parallel to the applied field H to reveal the structural details of these chains .