On the spin depolarization of a Hall ferromagnet in the vicinity of $\nu=1$ in two-dimensional electron systems based on ZnO

The behavior of the degree of spin polarization and the specific exchange energy near the Hall ferromagnetic state with filling factor $\nu=1$ in strongly interacting two-dimensional electron systems in MgZnO/ZnO heterostructures is investigated. These characteristics have been determined by measuring the spectra of inelastic light scattering by the collective excitations of the electron system, i.e., spin excitons and cyclotron spin-flip excitons. The intensity of the spin exciton line and the energy of the cyclotron spin-flip exciton line serve as indicators of the spin polarization of the system and the specific exchange energy at the lowest Landau level, respectively. It is found that no depolarization takes place when the filling factor deviates to $\nu<1$, whereas the system with $\nu>1$ is depolarized according to the single-particle scenario. The specific exchange energy decreases on both sides of $\nu=1$. It is shown that a local ferromagnetic order existing at $\nu=1$ also persists when the temperature is raised to $4.2$ K, which is somewhat lower than the Zeeman energy.