MACROSCOPIC QUANTUM TUNNELING OF MAGNETIZATION OF SINGLE FERRIMAGNETIC NANOPARTICLES OF BARIUM FERRITE

Presented are switching field measurements of individual ferrimagnetic and insulating BaFeCoTiO nanoparticles containing about 10(5) mu(B) a t very low temperatures (0.1-6 K). For temperatures higher than 0.4 K, the quantitative agreement with the Neel-Brown theory of thermal acti vated magnetization reversal allowed us to identify unambiguously the magnetization reversal of uniform rotation. Below 0.4 K, strong deviat ions from this model are evidenced which are quantitatively in agreeme nt with the predictions of the theory of macroscopic quantum tunneling of magnetization in the low dissipation regime.