Giant frequency dependence of dynamic freezing in nanocrystalline ferromagnetic LaCo0.5Mn0.5O3 -: art. no. 104402

We have investigated the magnetic properties of nanocrystalline LaCo0.5Mn0.5O3. The temperature dependence of the imaginary part of the ac susceptibility shows a strongly frequency-dependent maximum at a temperature T-f, which is well below the ferromagnetic transition temperature (T(c)similar to230 K). The frequency dependence of T-f obeys the Arrhenius relation, f=f(o) exp(-E-a/k(B)T), with physically reasonable values of f(o)=10(9) Hz and E-a/k(B)=1518 K. The frequency shift of T-f per decade of frequency is one of the highest values observed in any magnetic system, and a similarly large value is also found in LaCo0.4Mg0.1Mn0.5O3, suggesting that such behavior is intrinsic despite the apparent presence of long-range ferromagnetic order.