scaling in small-particle systems: low-temperature behaviour

Interaction effects and energy barrier distribution on the magnetic relaxation of nanocrystalline hexagonal ferrites

“…The fitted value of 2 is in reasonable agreement with that obtained from thermoremanent data ( ϭ0.38), while T B02 lies in between the peak of the blocking temperature distribution ͑81 K͒ and the maximum of the ZFC (T M ϭ 205 K͒, as found in other particulate systems. 3,4 Moreover, the total distribution function obtained from the fitting f (E) perfectly matches the effective distribution of energy barriers obtained from the derivative of the experimental master curve ͑see Fig. 8͒.…”

“…It was shown by both theoretical arguments and experimental results ͑see Ref. 4, and references therein͒ that, within the scope of the T ln(t/ 0 ) procedure, the effective distribution of energy barriers may be obtained from the experimental master curve by calculating the derivative of this curve with respect to T ln(t/ 0 ). Figure 8 displays this derivative, where an enhancement of the amount of the lowest energy barriers is evident.…”

“…It was also shown that, within the scope of this procedure, the effective distribution of energy barriers might be obtained from the experimental master curve. 4 In addition, numerical simulation studies suggested that an enhancement in the amount of the lowest energy barriers existed if dipolar interparticle interactions were demagnetizing. 5 These results were relevant when considering what is known as quantum tunneling of the magnetization.…”

Classical relaxation of magnetization in magnetic nanoparticles in the Kelvin regime

“…In the studies, temperature-independent magnetic viscosity has been observed at lower temperatures [1,3]. In order to clarify its origin, a scaling relationship was examined for relaxations of their remanent magnetization [2,5]. When thermally activated processes dominate the relaxations, the maximum height of surmountable barriers is k B T lnðt=t 0 Þ; where k B is the Boltzmann constant, T is the temperature, t is the time after removing the magnetic field, and t À1 0 is the attempt frequency.…”

“…Recently, relaxations of magnetization in nanomagnets have been intensively studied in order to verify the existence of macroscopic quantum tunneling of their magnetization vectors l (QTM) [1][2][3][4][5]. In the studies, temperature-independent magnetic viscosity has been observed at lower temperatures [1,3].…”