Damping dependence in dynamic magnetic hysteresis of single-domain ferromagnetic particles

It is demonstrated that both the area of the dynamic magnetic hysteresis (DMH) loop and the volume power loss of an assembly of uniaxial superparamagnetic nanoparticles with a random distribution of easy axes are very sensitive to damping at low, intermediate, and high frequencies. In particular, a dynamical regime that is resonant in character occurs in the vicinity of the ferromagnetic resonance (FMR) frequency for low to moderate values of the alternating current (ac) field amplitude. The resonant regime is characterized by a diamagnetic-like response of the particles, resulting from a phase lag of the stationary nonlinear magnetization with respect to the applied field greater than π/2.

Figure 1

DMH loops [$m\left(t\right)=M_H\left(t\right)/M_S$ vs $h\left(t\right)=(\xi /2\sigma )\cos \omega t$] at quasistatic and intermediate frequencies for various values of the damping parameter α.

Figure 2

DMH loop area vs the damping parameter at quasistatic and intermediate frequencies.

Figure 3

Real and imaginary parts of $\chi \left(\omega \right)=2\overline{m_1^1}/\xi$ vs $\omega {\tau }_0$ in the FMR region.

Figure 4

Resonant DMH loops for various values of the damping parameter α.

Figure 5

Area of the resonant DMH loop vs the damping parameter α.