## 1 Introduction  
Nowadays magnetorheological elastomer (MRE) has attracted much attention since, in addition to its magnetic and rheological properties, it presents uncommon electrical properties leading to various engineering applications, for example, vibration absorbers [1; 2; 3], electromagnetic waves absorbers [4], dampers [5; 6], and sensors [7; 8]. MREs are smart materials with properties that can be altogether changed in a controlled manner by outer stimuli, for example, magnetic field, electric-magnetic field, temperature, and pH [9; 10]. The sensitivity to the magnetic field is provided by magnetic nano- or microparticles incorporated into the polymer [11; 12]. In general, the ultimate properties of MREs are subject to the magnetic particle, elastomer matrix, external magnetic field strength, and dispersion of particles in the elastomer matrix. Up to now, carbonyl iron particles (CIPs) have been commonly used as magnetic particles in MRE. The particles are dispersed in numerous types of rubber matrixes such as natural rubber or silicone rubber [13; 14; 15]. Although this kind of magnetic particles exhibit a high magnetic saturation of elements as well as high permeability and low remnant magnetization, the electrical property investigation is still lacking in the previous study, in which researchers chose to add another filler, which is graphite (Gr) [16]. The introduction of Gr powder has been proved to generate a new electrical conductivity property, while maintaining the existing rheological properties of MRE. [PERSON] et al. introduced a force sensor utilizing Gr powder in a magnetorheological elastomer (Gr-MRE); the effect of the magnetic field on the resistivity response of the fabricated samples was tested using an experimental setup that included mechanical parts, an electrical circuit, and an LED display unit. The results revealed that the prototype force sensor could be used to detect the external forces at the selected force ranges [17]. On the other hand, [PERSON] et al. fabricated two types of Gr-MRE by varying the conditions between isotropic and anisotropic. This difference in particle structure contributed toward the increment in the initial storage and loss moduli under the anisotropic condition, which explains that charge transport plays a significant role in the dielectric polarization in the anisotropic composite material containing magnetic particles within the matrix [18]. In different circumstances, [PERSON] et al. [19] analyzed an electroconductive MRE exhibiting highly complex resistive behavior. The author used CIPs, carbon black, and silicone as the main ingredients for the MRE fabrication. The results revealed that the resistance increased from 100 to 2300 k\(\Omega\) and then dropped exponentially to 1200 k\(\Omega\) at 1% and 3% strain, which was within the linear elasticity region. In a most recent study, [PERSON] et al. [20] investigated the resistance properties of MRE by introducing Gr powder mixed with CIPs. The author used Gr particles in order to achieve a high electrical conductivity. However, the mixture of CIPs and Gr caused the composition to be saturated and thus restricted the author to add more Gr to the composition; otherwise, the samples would be too brittle and not reliable. Nevertheless, several studies have introduced the cobalt as magnetic particles in MRE. [PERSON] et al. [21] studied the effect of cobalt shape on improving the interfacial interaction of MRE based on a cobalt-silicon rubber matrix, which indicated good storage modulus and MR effect. In their study, an anisotropic MRE with two types of particle shape, namely flower-like and spherical shape, were fabricated and analyzed. The result showed that the flower-like shape cobalt particles exhibited a higher performance of storage modulus for the frequency sweep test as compared to the spherical shape. However, only rheological and magnetic properties were reported in the study.