Nuclear forward scattering application to the spiral magnetic structure study in $ε − $Fe$_ 2$O$_3$

Physical review / B 101(9), 094408 (2020). doi:10.1103/PhysRevB.101.094408
The $ε − $Fe$_ 2$O$_3$ 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 4–300K in applied magnetic fields of 0–4T 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 H$_{hf}$(T) behavior, but makes a strong opposite impact on the hyperfine fields in the nonequivalent iron sites, leading to the divergence of H$_{hf}$ polar angle dependences below 80 K. A complete diagram of the $ε − $Fe$_ 2$O$_3$ magnetic structure in the temperature range of 4–300K is proposed. At 300 K, the $ε − $Fe$_ 2$O$_3$ compound is confirmed to be a collinear ferrimagnet. The experimental results show that the magnetic transition at 150–80K 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.
Published by Inst., Woodbury, NY