Power losses in a suspension of magnetic dipoles under a rotating field

Energy absorption due to viscous friction in a dilute suspension of single-domain ferromagnetic particles subjected to a rotating field is considered. The problem is treated in the framework of kinetic approach. The behavior of specific loss power (SLP) as a function of the field amplitude and frequency is studied. It is shown that for either of these parameters (while the other is kept constant) SLP first grows quadratically and then saturates. The cases of a rotating field and oscillating fields are compared, and the essential differences are revealed. The results obtained enable one to assess the allowable or optimal field parameters for a given magnetic suspension intended for rotational magneto-inductive heating.

Figure 1

Frequency dependence of the transversal magnetization for the rotating field amplitudes $\xi =2$ (1), 5 (2), 10 (3), 25 (4), and the athermal limit $\xi =\infty$ (dashed).

Figure 2

Specific loss power for rotating (a) and oscillating (b) fields; function $\mathcal{S}$ is normalized according to Eq. (24).

Figure 3

Specific loss power in a rotating field as a function of (a) magnetic field strength for $\omega {\tau }_0=0.2$ (1), 1 (2), 2 (3), 5 (4) and (b) field rotation frequency for $\xi =2$ (1), 5 (2), 10 (3), 20 (4); in both panes the asterisks mark the points corresponding to the condition $\omega {\tau }_0=1/2$.

Figure 4

Specific loss power in an oscillating field as a function of (a) magnetic field strength for $\omega {\tau }_0=0.2$ (1), 1 (2), 2 (3), 5 (4) and (b) field rotation frequency $\xi =2$ (1), 5 (2), 10 (3), 20 (4).

Figure 5

Comparison of specific loss power vs frequency for rotating (curves 1) and oscillating (curves 2) fields at $\xi =5$ (a) and $10$ (b).

Figure 6

Energy absorption per cycle for a particle subjected to a rotating (1) or oscillating (2) field; values of the field strength parameter $\xi$ are $\infty$ (dashed) and $10$ (solid).