Nuclear forward scattering application to the spiral magnetic structure study in epsilon-Fe2O3

Knyazev, Yu, V; Chumakov, A., I; Dubrovskiy, A. A.; Semenov, S., V; Sergueev, I. Yakushkin, V. L. Kirillov, O. N. Martyanov, and D. A. Balaev Physical Review B. DOI: 10.1103/PhysRevB.101.094408

The -Fe2O3 magnetic structure has been analyzed using the synchrotron radiation source. Time spectra of nuclear forward scattering for isolated nanoparticles with an average size of 8 nm immobilized in a xerogel matrix have been recorded in the temperature range of 4–300 K in applied magnetic fields of 0–4 T in the longitudinal direction at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). It has been found that the external magnetic field does not qualitatively change the Hhf (T) behavior, but makes a strong opposite impact on the hyperfine fields in the nonequivalent iron sites, leading to the divergence of Hhf polar angle dependences below 80 K. A complete diagram of the -Fe2O3 magnetic structure in the temperature range of 4–300 K is proposed. At 300 K, the -Fe2O3 compound is confirmed to be a collinear ferrimagnet. The experimental results show that the magnetic transition at 150–80 K leads to the formation of a noncollinear magnetic structure. Furthermore, in the range of the 80–4 K, the ground state of a magnetic spiral is established. The experimental results are supplemented by the analysis of the exchange interactions and temperature dependence of the magnetization in a magnetic field of 7 T.