Magnetic relaxation and quantum tunneling in nanocrystalline particles

Low-temperature magnetic relaxation phenomena have been studied in two samples consisting of nanocrystalline γ-Fe2O3and polymer in either water (as ferrofluid) or in potassium silicate (as glass). The relaxation of the magnetization follows a logarithmic law and the magnetic viscosity, S, tends to be independent of temperature below 2.1 K for the glass sample, giving evidence of macroscopic quantum tunneling of the magnetization.