Xx. Zhang et al., MAGNETIC-RELAXATION AND QUANTUM TUNNELING IN NANOCRYSTALLINE PARTICLES, Journal of magnetism and magnetic materials, 140, 1995, pp. 1853-1854
Low-temperature magnetic relaxation phenomena have been studied in two
samples consisting of nanocrystalline gamma-Fe2O3 and polymer in eith
er water (as ferrofluid) or in potassium silicate (as glass). The rela
xation 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.