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 prepared 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 Т_P < T < T*) is described by the expression: 2πν/γ = Н_R + H^A_{(T = 0)}(1 – T/Т*), where γ is the gyromagnetic ratio, H_R is the resonance field. The induced anisotropy H^A is due to the spin-glass state of the near-surface regions. T_P temperature characterizes the energy of the interparticle interaction of nanoparticles.