The features of the magnetic structure of ultrasmall \(\epsilon \) -Fe2O3 nanoparticles have been studied by the nuclear forward scattering technique using synchrotron radiation. The sample consists of isolated \(\epsilon \) -Fe2O3 nanoparticles with an average size of \(\langle d\rangle = 3.8\) nm immobilized in a SiO2 xerogel matrix. The time-domain spectra have been measured in the temperature range of 4–300 K in zero external magnetic field and field \(H = 4\) T applied in the longitudinal direction. The character of the change in the hyperfine field Hhf as a function of the external magnetic field is the same in the entire temperature range: unlike large \(\epsilon \) -Fe2O3 particles, a monotonic increase in Hhf is observed in the external field. These results indicate that there is no magnetic transition in the temperature range of 80–150 K for ultrasmall (smaller than \( \approx \) 9 nm) \(\epsilon \) -Fe2O3 particles, and the magnetic structure is noncollinear in the range of 4–300 K.
