*2.2. Samples Characterization*

The A1 and A2 morphological image related to the surface and structure of the nanosized Ni-Mg cobalt-ferrite particles were observed using an ultra-high resolution of Field Emission Scanning Electron Microscopy (FESEM), (JSM-7601F, JEOL, Akishima, Tokyo, Japan) at a voltage of 2.0 kV and a magnification of 50,000<sup>×</sup>. Concurrently, the cross-sections of MRE samples were observed using Scanning Electron Microscopy (SEM), (JSM-IT300LV, JEOL, Akishima, Tokyo, Japan) at a voltage of 5 kV. In order to examine the magnetic properties of all MRE samples, a Vibrating Samples Magnetometer (VSM) (MicroSense, FCM-10, LLC, MA, USA) was used to measure the magnetic properties of the MRE samples. The samples were subjected to the magnetic field in the range of −15 kA/m to +15 kA/m. Meanwhile, the e ffect of various magnetic fields towards the rheological properties of all MRE samples were evaluated using a rheometer (MCR 302, Anton Paar, Graz, Austria) under oscillation mode at room temperature (25 ◦C). All samples were subjected to di fferent magnetic fields, ranging from 0 to 5 A (refer to Table 1) and the Tesla unit is used. The experiment is repeated for three times in order to ge<sup>t</sup> the consistency of the result obtained. The strain sweep test was carried out by varying the strain from 0.001% to 100%, with a constant frequency of 1 Hz, whereas another test for the current sweep was carried out by varying the magnetic fields from 0 to 5 A, with a constant strain and frequency of 0.01% and 1 Hz, respectively. The electrical resistance properties of all MRE samples (circular shape with a thickness of 1 mm, diameter of 20 mm) were evaluated using a test rig with di fferent forces in order to analyze the electrical resistance behavior. The set-ups were almost the same as the one reported by Shabdin et al. [4]; however, a small modification has been made, in which some load cells have

been attached in order to obtain the accuracy of the force, as shown in Figure 2. The test rig consists of data acquisition (DAQ) obtained from the LabVIEW software (6211, National Instruments, Austin, TX, USA). Different loads in the range of 0 to 600 g, increasing in increments of 50 g, were placed on the MRE samples in the absence and presence of a magnetic field. The test was repeated three times in order to obtain the consistency of the electrical resistance of the MRE samples.


**Table 1.** Magnetic flux density of the MRE samples.

**Figure 2.** Test rig for the conductivity test.
