## 3 Results and Discussion
### Magnetic Properties of Fe\({}_{65}\)Ni\({}_{35}\) and Fe\({}_{65}\)Mn\({}_{35}\) Alloys  
Temperature-dependent DC magnetization curves, obtained under zero-field-cooled (ZFC) and field-cooled (FC) conditions at H = 1 kOe for Fe\({}_{65}\)Ni\({}_{35}\) and Fe\({}_{65}\)Mn\({}_{35}\), are shown in Figure 3a,b, respectively. In this study, we have recorded the temperature-dependent magnetization data in the temperature range of 50 K to 400 K. In the case of the Fe\({}_{65}\)Ni\({}_{35}\) alloy, as displayed in Figure 3a, it is noticed that as the temperature decreases, bifurcation among the ZFC and FC curves increases up to the lowest measured temperature. However, the ZFC and FC curves have not merged up to the highest measured temperature, i.e., 400 K. This substantiates that Fe\({}_{65}\)Ni\({}_{35}\) has a magnetic ordering at a higher temperature, as reported in the literature [22; 23; 24]. Additionally, determining the blocking temperature, in this case, is very difficult because of the absence of any clear/sharp peak in the ZFC magneiza  
Figure 1: Room temperature X-ray diffraction pattern (XRD): (**a**) XRD results for Fe\({}_{65}\)Ni\({}_{35}\); (**b**) XRD results for Fe\({}_{65}\)Mn\({}_{35}\). Figure 2: SEM micrograph: (**a**) SEM image for Fe\({}_{65}\)Ni\({}_{35}\); (**b**) SEM image of Fe\({}_{65}\)Mn\({}_{35}\). tion plot. This behavior may arise from the presence of different Fe-Ni magnetic clusters of the \(\alpha\) and \(\gamma\) phases, either ferromagnetic or super-paramagnetic [26]. Interestingly, arc-like behavior has appeared in ZFC magnetization, followed by an abrupt change in the slope just above 250 K, perhaps due to competition between two different structural/magnetic clusters, and the abrupt change in the slope occurred due to the dominance of the concerned phase in that particular temperature region. In order to check the presence of any magnetic ordering within this measured temperature range, we further analyze the derivative curve of the magnetization data (not shown), confirming a broad minimum of around 260 K. For the case of Fe\({}_{65}\)Mn\({}_{35}\), ZFC and FC magnetization do not merge in common with Fe\({}_{65}\)Ni\({}_{35}\) in the measured temperature range (as shown in Figure 3b). However, the nature of the magnetization curves changes as the temperature increases. The ZFC and FC plot depicts a small peak around 320 K. The reason behind this peak and curve modification is the coexistence of two magnetic correlations, i.e., ferromagnetic and antiferromagnetic. Such antiferromagnetic correlations in these alloys are not unusual. They also sometimes depend on the presence of two crystallographic phases. This statement consent with the literature reports, which communicate that FeMn compounds have crystallographic phase-controlled magnetic properties, i.e., \(\gamma\)-FeMn has antiferromagnetic behavior [41]. In order to obtain better insight into the magnetic nature of the compound, investigating the isothermal magnetization as a function of the applied magnetic field is necessary, along with conducting a temperature-dependent magnetization study. Isothermal magnetization (M) behavior as a function of the applied magnetic field (H) was obtained up to \(\pm\)30 kOe in the temperature range 50 K to 400 K. Representative curves at different temperatures (50 K and 300 K) for Fe\({}_{65}\)Ni\({}_{35}\) and Fe\({}_{65}\)Mn\({}_{35}\) are shown in Figure 4a,b, respectively. Both compounds have shown a small magnetic hysteresis below 4 kOe, and magnetization follows a saturation. This type of behavior supports the existence of the ferromagnetic state. For the Fe\({}_{65}\)Ni\({}_{35}\) case, at 50 K, the magnetization shows complete saturation around  
Figure 3: Temperature response of DC magnetization results measured at 1 kOe under zero field cooled (ZFC) and field cooled (FC) conditions: (**a**) ZFC and FC magnetization curve for Fe\({}_{65}\)Ni\({}_{35}\); (**b**) ZFC and FC magnetization curve for Fe\({}_{65}\)Mn\({}_{35}\).