Collective spin glass state in nanoscale particles of ferrihydrite

Ferromagnetic resonance was used to study three types of ferrihydrite nanoparticles: nanoparticles formed as a result of the cultivation of microorganisms Klebsiella oxytoca; chemically ferrihydrite nanoparticles; chemically prepared ferrihydrite nanoparticles doped with Cu. It is established from the ferromagnetic resonance data that the frequency-field dependence (in the temperature range $T_{\operatorname{P}}<T<T^*$) is described by the expression: 2$\pi\nu/\gamma = H_{\operatorname{R}}+T^{\operatorname{A}}_{(T =0)}\cdot (1-T/T^*)$, where $\gamma$ is the gyromagnetic ratio, $H_{\operatorname{R}}$ is the resonance field. The induced anisotropy $H_{\operatorname{A}}$ is due to the spin-glass state of the near-surface regions. $T_{\operatorname{P}}$ temperature characterizes the energy of the interparticle interaction of nanoparticles.