# Unexpected Ferromagnetism--A Review
## 3 Drawbacks of Unexpected Ferromagnetism
Two different categories of sources of possible errors when these samples were manipulated for magnetic measurements using SQUID (superconducting quantum interference devices) or VSM (vibrating sample magnetometers) were identified:  
* Material contaminations in a homogeneous manner which seems to be proportional to their weight and can be identified by careful chemical analysis; and
* Specific contaminations during the procedure of measurement, which include the sample fixation in a certain geometry inside apparatus and that can produce a false signal, which do not depend on the sample mass and can be due to stainless-steel tools such as tweezers or fine blades, polyimide Kapton tape, plastic tubes (straws), gelatin capsules, cotton, silver conductive paint, and inks iron/iron oxide-contaminated or even anisotropy artifacts [114]. For example, the sticky Kapton tape, which is usually employed to attach the samples on their holders, can be simply contaminated by magnetic air dust microscopic particles and can induce ferromagnetic or paramagnetic signals between 10\({}^{-4}\) and 10\({}^{-5}\) emu [113]. Moreover, due to the fact that the magnetic measurements in SQUID or VSM are based on the principle of magnetic induction in a nearby coil, which occurs when a variable magnetic flux across the coil is used, this flux will be influenced by the sample magnetic moment and also by the sample orientation and distance towards the center of coil, thus the resulted magnetic signal in the case in inhomogeneous contamination will depend by the sample position [113]. Moreover, the sources of ferromagnetism that are foreign to the sample associated with integral magnetometry measurements, especially by SQUID technique, were carefully revised in a more recent paper by [PERSON] et al. [115]. He also found two categories of possible errors: The first being related to the experimental setup that results in misidentification of the magnetic state of the sample and the second being considered as accidental magnetic contaminations, as classified in [113], which cannot necessarily be only those deposed on sample surface but also can be incorporated in the sample [115]. The SQUID device itself can be capable of \"emulating ferromagnetism where it does not exist\", due to the generation in some cases of a residual ferromagnetic-like hysteresis curve, due to differences in the ideal behavior of power supply and the magnetic superconducting coil [113]. They also classified the sources of contamination as being from cleaning and handling, sample mounting (where the constraints of the free-standing method were highlighted), sample substrate, and high-temperature processing and/or annealing of the sample (problem of contamination by evaporation/condensation of heated metallic parts), finishing with \"accidental contamination even in metal-free conditions\" (by solvents/ ultrasonication) [115]. Additionally, the author of [115] discussed the instrumental artifacts in three paragraphs:  
* False (spurious) ferromagnetism originating from the magnetometer magnetic field non-uniformity, resulting in errors that become important for the case of nanomaterials with a magnetic signal much lower than those of the diamagnetic signal of their substrate;
* Features associated with non-intrinsic ferromagnetism (such as those derived from the asymmetry of ferromagnetic volume versus the center of the moment in the case of the uniformly magnetized diamagnetic sample);
* Intrinsic-like features associated with non-intrinsic ferromagnetism (anisotropy artifacts linked to axial or radial effects). The difficulty of the study of the intrinsic FM in dilute magnetic nanomaterials is considered in [115] to be related to their complicated phase diagrams, not only from the structure point of view but also from the magnetic behavior. From the first, these materials can be situated from truly diluted systems up to more or less segregated systems.