Magnetodielectric properties of magnetoactive elastomers comprising micrometer-sized iron particles dispersed in compliant elastomer matrices are experimentally studied in stepwise time-varying dc magnetic fields. It is found that imposition of magnetic field significantly increases both the effective lossless permittivity of these composite materials as well as their effective conductivity. These magnetodielectric effects are more pronounced for larger concentrations of soft-magnetic filler particles and softer elastomer matrices. The largest observed relative change of the effective dielectric constant in the maximum magnetic field of 0.57 T is of the order of 1000%. The largest observed absolute change of the loss tangent is approximately 0.8. The transient response of the magnetodielectric effect to a step magnetic-field excitation can be rather complex. It changes from a simple monotonic growth with time for small magnetic-field steps (<0.1 T) to a non-monotonic behavior with a significant rapidly appearing overshoot for large magnetic-field steps (>0.3 T). The settling time to the magnetic-field step excitation can reach roughly 1000 s and it depends on the applied magnetic field and sample composition. There is also significant hysteresis of the magnetodielectric effect on the externally applied magnetic field. These findings are attributed to the rearrangement of ferromagnetic filler particles in external magnetic fields. The results will be useful for understanding and predicting the transient behavior of magnetoactive elastomers in applications where the control magnetic field is time dependent.

在逐步变化的直流磁场中，对包含微米级铁颗粒的磁活性弹性体的磁介电性能进行了实验研究。发现施加磁场显着增加了这些复合材料的有效无损介电常数以及它们的有效电导率。对于较大浓度的软磁填料颗粒和较软的弹性体基质，这些磁电效应更为明显。在最大磁场0.57 T中观察到的最大有效介电常数的相对变化约为1000％。观察到的最大损耗角正切绝对变化约为0.8。磁电效应对阶跃磁场激励的瞬态响应可能相当复杂。它从小磁场步长（<0.1 T）随时间的简单单调增长变为大磁场步长（> 0.3 T）时迅速出现明显过冲的非单调行为。磁场步进激发的建立时间大约可以达到1000 s，这取决于所施加的磁场和样品成分。磁电效应在外部施加的磁场上也存在明显的滞后现象。这些发现归因于铁磁性填料颗粒在外部磁场中的重排。