engleski

Magnetic dynamics in K3Fe5F15 family of multiferroics

Magnetoelectric multiferroics K3Fe5F15, K3Fe3Cr2F15 and K3Cu3Fe2F15 were found to have magnetic transition at 122K, 36K and 28K, respectively, below which the splitting between zero-filed cooled and field cooled magnetization curves is present. In order to study the magnetic behaviour below this temperature, the detailed investigation of magnetic relaxation after change of the magnetic field and temperature is performed. Slow relaxation on time scale of hours is in accordance with the splitting between zero-filed cooled and field cooled magnetization curves and a.c. magnetic susceptibility, as well as with onset of irreversibility of magnetization vs. field curves. Logarithmic relaxation of magnetization in time is a sign of the distributed barriers which block the magnetic moments against the reorientation. Temperature dependence of the logarithmic relaxation rate and other parameters could be understood within a model of thermal activation of magnetic moments of clusters distributed over barriers. There are differences in temperatures and fields needed to induce the relevant relaxation of magnetization. While in K3Fe5F15 the relaxation is observable even in 1T field in the whole temperature range, for K3Cu3Fe2F15 it is no more seen in 0.1T field, and for K3Fe3Cr2F15 in 1T it is seen only at the lowest temperatures. The results point to the presence of two magnetic subsystems with different energy scales responsible for magnetic dynamics. D.P. thanks the financing from Ad Futura (Slovenia) and NZZ (Croatia).

multiferroic; magnetic relaxation; magnetic clusters

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