*3.2. Magnetic Properties*

The magnetic properties of all MRE samples were measured continuously under magnetic fields in the range of −15 kA/m to 15 k/Am. Figure 5 displays the hysteresis loop of the MRE samples. As shown in Figure 5, the MRE+A1 sample exhibits the highest magnetic saturation, Ms, at 143.92 emu/g, followed by the MRE + A2 sample, at 143.77 Am<sup>2</sup>/kg, and control MRE at 140.25 Am<sup>2</sup>/kg.

**Figure 5.** Magnetization curves for all MRE samples.

The summary and comparison of all MRE samples and previous magnetic properties of A1 and A2 are shown in Table 2. The MREs with A1 and A2 exhibit an enhancement of magnetic saturation up to 2% as compared to the control MRE. Due to a higher surface area of the nanosized Ni-Mg cobalt-ferrites, it is believed that this nanoparticle fills the void between the CIPs and resulted in enhancement of the CIPs bonding. In addition, the magnetic remanence, Mr, of MRE with A1 and A2, showed a sharply decreasing value, in the range of 4200% and 4800%, as compared to the nanosized Ni-Mg cobalt-ferrite itself. As a matter of fact, lower remanence is required in any device, particularly in sensor applications as the material in the sensor is highly sensitive to the environment and must have a fast response. As such, the control MRE demonstrates the lowest remanence of 0.32 Am<sup>2</sup>/kg as compared to the MRE with A1 and A2. Furthermore, the coercivity, Hc, of the control MRE is also low at 8.70 Oe, while the MRE with A1 and A2 exhibit increases of 81% and 76%, respectively, in comparison to the control MRE. The increase in the coercivity and remanence of MRE with A1 and A2 are believed to be due to the high surface area of the nanosized Ni-Mg cobalt-ferrites, which resulted in easy movement of the nanosized Ni-Mg cobalt-ferrites that were attracted to the magnetic field. By implementing only these types of filler in MRE fabrication, notably, the magnetic properties exhibit larger changes, particularly in terms of remanence and coercivity behavior, which make this type of filler a potential candidate for use in the development of sensors.

**Table 2.** Summary of the nanosized Ni-Mg cobalt ferrites and all MRE samples.

