Giant frequency dependence of dynamic freezing in nanocrystalline ferromagnetic LaCo0.5Mn0.5O3

TL;DR

This study reveals a giant frequency dependence of dynamic freezing in nanocrystalline LaCo0.5Mn0.5O3, indicating intrinsic magnetic relaxation phenomena with unusually high frequency shift values.

Contribution

It demonstrates the exceptionally large frequency dependence of the freezing temperature in nanocrystalline LaCo0.5Mn0.5O3, highlighting an intrinsic magnetic relaxation behavior.

Findings

Frequency dependence of Tf follows Arrhenius law.

High frequency shift per decade observed.

Similar behavior found in LaCo0.4Mg0.1Mn0.5O3.

Abstract

We have investigated the magnetic properties of nanocrystalline LaCo0.5Mn0.5O3. The temperature dependence of the imaginary part of the a.c. susceptibility shows a strongly frequency dependent maximum at a temperature, Tf, which is well below the ferromagnetic transition temperature (TC ~ 230 K). The frequency dependence of Tf obeys the Arrhenius relation, f = foexp(-Ea/kBT), with physically reasonable values of fo = 109 Hz and Ea/kB = 1518 K. The frequency shift of Tf 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.