**Enhancement of Viscoelastic and Electrical Properties of Magnetorheological Elastomers with Nanosized Ni-Mg Cobalt-Ferrites as Fillers**

**Siti Aishah Abdul Aziz 1, Saiful Amri Mazlan 1,2,\*, U Ubaidillah 3,4,\*, Muhammad Kashfi Shabdin 2, Nurul Azhani Yunus 5, Nur Azmah Nordin 1, Seung-Bok Choi 6,\* and Rizuan Mohd Rosnan 7**


Received: 8 August 2019; Accepted: 17 September 2019; Published: 28 October 2019

**Abstract:** Carbon-based particles, such as graphite and graphene, have been widely used as a filler in magnetorheological elastomer (MRE) fabrication in order to obtain electrical properties of the material. However, these kinds of fillers normally require a very high concentration of particles to enhance the conductivity property. Therefore, in this study, the nanosized Ni-Mg cobalt ferrite is introduced as a filler to soften MRE and, at the same time, improve magnetic, rheological, and conductivity properties. Three types of MRE samples without and with di fferent compositions of Mg, namely Co0.5Ni0.2Mg0.3Fe2O4 (A1) and Co0.5Ni0.1Mg0.4Fe2O4 (A2), are fabricated. The characterization related to the micrograph, magnetic, and rheological properties of the MRE samples are analyzed using scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and the rheometer. Meanwhile, the e ffect of the nanosized Ni-Mg cobalt ferrites on the electrical resistance property is investigated and compared with the di fferent Mg compositions. It is shown that the storage modulus of the MRE sample with the nanosized Ni-Mg cobalt ferrites is 43% higher than that of the MRE sample without the nanomaterials. In addition, it is demonstrated that MREs with the nanosized Ni-Mg cobalt ferrites exhibit relatively low electrical resistance at the on-state as compared to the o ff-state condition, because MRE with a higher Mg composition shows lower electrical resistance when higher current flow occurs through the materials. This salient property of the proposed MRE can be e ffectively and potentially used as an actuator to control the viscoelastic property of the magnetic field or sensors to measure the strain of the flexible structures by the electrical resistance signal.

**Keywords:** magnetorheological elastomer; filler; hetero-aggregation; nanosized Ni-Mg cobalt ferrites; electrical resistance; resistivity; rheological properties
