## 5 Discussion  
In this article, the main techniques and the most important devices existing in the international literature to perform magnetic sensing of ferromagnetic nano-particles are presented. Table 3 summarizes the different types of magnetometers that can be used for magnetic measurements and presents an overview of their advantages and disadvantages for the specific application. Figure 11: The magnetic field values, when the sample is absent, are derived from the two magnetometers in (**a**) x axis, (**b**) y axis, and (**c**) z axis. \begin{table}
\begin{tabular}{c c c c} \hline
**Magnetometer Type** & **Advantages** & **Disadvantages** & **Related References** \\ \hline  & & & Costly \\  & & & Low sensitivity \\  & & & Continus build electromagnets \\  & & & Continus moving parts \\  & & & Continus moving parts \\  & & & Overall complex construction \\  & & & The low time resolution of the signal \\  & & & Bad quality of signal-to-noise ratio \\ \hline  & & Provides reduced target-field distance \\  & & Flexibility in the positioning & & \\  & & Absence of cryogenic coating & \\  & & Measures the absolute magnetic field & \\ \hline  & & & Limited use for quantitative measurements \\  & & & \\  & & & High level of noise & \\  & & & Long-term displacements of the signal \\ \hline  & & & \\  & & Small dead time, less than 1s & \\  & & Can characterize the nanoparticles with accuracy, even if the & \\  & & distance between the sensor and the target is small & \\ \hline  & & Compact & \\  & & Mechanical & \\  & & High sensitivity & \\  & & Large-scale device & \\ \begin{table}
\begin{tabular}{c c c c} \hline
**Magnetometer Type** & **Advantages** & **Disadvantages** & **Related References** \\ \hline \multicolumn{4}{c}{The signal has a proportional relationship with the magnetic} \\ \multicolumn{4}{c}{High density} \\ \multicolumn{4}{c}{Low noise levels (\(\mathrm{P}\) of \(\mathrm{P}\) of \(\mathrm{P}\) at \(1\mathrm{\,Hz}\))} \\ \multicolumn{4}{c}{White-noise values in the range of a few \(\mathrm{P}\)/\(\mathrm{T}\)/\(\mathrm{Hz}^{2}\)} \\ \multicolumn{4}{c}{Alle to work at room temperatures} \\ \multicolumn{4}{c}{Plugate} \\ \multicolumn{4}{c}{Simple structure without moving items} \\ Magnetometer & High precision & Are limited by their bandwidth in the lower \(\mathrm{kHz}\) range & [8,19,20,27,42,45,67, 110,121-129] \\ \multicolumn{4}{c}{No need for cryogenic cooling} \\ \multicolumn{4}{c}{No need for magnetic shielding} \\ \multicolumn{4}{c}{Measure the absolute value of the magnetic field} \\ \multicolumn{4}{c}{Alle to know the signal forces to deactivation} \\ \multicolumn{4}{c}{Application in the magnetic fields between \(20\,\mathrm{P}\)/\(\mathrm{T}\) and \(100\,\mathrm{nT}\)} \\ \end{tabular}
\end{table} 
Table 3: Conf. From the literature investigation, it is proved that the most commonly used instruments are the SQUIDs and the fluxgate magnetometers, although, observing Table 3, it can be seen that the fluxgate magnetometer displays the most advantages, relevant to catalysis monitoring, and it is a promising measurement instrument for nanoparticle characterization. These magnetometers present high precision, low noise levels, and simple structure; are applicable in a great range of magnetic fields; do not need cryogenic cooling and magnetic shielding, etc. compared with other types of magnetometers. The most important parameter is the cost analysis of the fluxgate sensors. For this reason, these measurement instruments will be the foundation of a novel, accurate, and cost-effective system for magnetic characterization purposes as a next step of this work. The preliminary study is summarized in the last section of the article, where the magnetization and the position of a cobalt-based magnetic material are calculated using a dual fluxgate arrangement. It turns out that this experimental setup can detect the magnetization with accuracy, as well as the position of the sample, enabling the 2D mapping of the active remaining catalyst as a feasible process.