## 3 Magnetic Characterization Instruments
### Vibrating Sample Magnetometers  
This type of magnetometer is one of the oldest technologies in the field of magnetic sensing of ferromagnetic materials. Starting from the 1960s until today, three different basic VSM setups have been proposed. The first was presented by the Centre National de la Recherche Scientifique (CNRS) in Paris, and it was a sensor for catalyst sensing in the ambient environment [63]. The second setup was based on acoustic oscillations [64]. The third setup was proposed by the Department of Chemical Engineering at the University of Cape Town in collaboration with scientists at Sasol R&T. To the authors' knowledge, only these three setups are still active for sensing purposes, as the VSMs are devices that present problems and tend to be replaced with other magnetic sensor instruments or open the way for the use of hybrids of coiled magnetometers and magneto-optical devices.  
The vibrating sample magnetometer, a costly and with low sensitivity device, contains bulky electromagnets as well as moving parts and an overall complex construction, compared to SQUIDs and fluxgate magnetometers [26]. According to the market prices, a VSM costs about 300 k\(\upmu\)c, and this price does not include the extra cost for the integration of the chemical reactor. Moreover, the time resolution of the signal is low, without the ability to be resolved in space. Another important issue that the vibration sample magnetometer has to face is the signal-to-noise ratio, which should be even more improved for this device to achieve accurate measurements [65]. In addition, according to [66], the VSM method demands a significant amount of time, and for this reason, it is not very efficient for clinical applications. Finally, the VSM demands mechanical vibration, while only few VSM implementations provide operation under gaseous atmospheres using a single measuring setup with the ability to face temperature levels up to 600 \({}^{\circ}\)C and pressure levels up to 50 bar.  
The most important studies that use vibration sample magnetometers for nanoparticle materials characterization purposes are summarized below. Analytically, in [65], \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles, used for medical applications are measured through a vibrating sample magnetometer. In [66], a vibrating sample magnetometer is used to provide magnetic information about formalin-fixated lymph nodes, with the further aim of this information to be used to construct a clinical magnetometer, instead of the vibrating sample magnetometer. In [67], the VSM was used for the characterization of Cobalt ferrite CoFe\({}_{2}\)O\({}_{4}\) crystalline nanoparticles with sizes between 50 and 100 nm. In [68], three different methods, the XRD, the TEM, and the VSM, are used for the characterization of CoFe\({}_{2}\)O\({}_{4}\) nanopowders. In [69], a vibration sample magnetometer is used for determining the magnetic characteristic of Fe\({}_{3}\)O\({}_{4}\)/polystyrene composite particles. In [70], cobalt ferrite nanoparticles, as well as nanorods and porous nanoparticles to methanol, are characterized and compared. For magnetic characterization purposes, the XRD, the SEM, and the VSM methods are applied. In [71], magnetic thioflavin-T silica-coated nanoparticles, used for medical purposes, are characterized using the XRD method, TEM method, VSM method, and Fourier transform infrared spectroscopy. In [72], characteristics of synthesized ferrofluid are measured using various methods including the VSM method. In [73], a vibrating sample magnetometer is used for magnetic measurements in creative proteins, and the method is proven simpler and more economical than a method that uses a SQUID magnetometer. In [74], Ni\({}_{1-x}\)Zn\({}_{x}\)Fe\({}_{2}\)O\({}_{4}\) nanoparticles are characterized using the XRD method, TEM method, Fourier transform infrared, and VSM method. Finally, in [75], the VSM method is applied, among other methods, for magnetic characterization purposes of iron oxide nanoparticles functionalized with carboxyl groups.