The Electromagnetic Nature of Nanoparticles

Note: The electromagnetic nature of nanoparticles in magnetic materials, the molecules and atoms that make them up  have electromagnetic properties. In simpler terms, elements such as iron, cobalt, nickel and their alloys that  are attracted  by a magnet are called magnetic materials.

The classification of electromagnetic materials is based on magnetic susceptibility (the ability of a material to become magnetized). Based on this, materials are classified into three groups: ferromagnetic, paramagnetic, and diamagnetic. The resultant dipole moment in electromagnetic diamagnetic materials is zero, and in the presence of a magnetic field, a  dipole moment is induced in them; but the direction of these induced dipoles  is opposite to the direction of the external magnetic field, which causes the material (diamagnetic) to be repelled from the magnetic field. By removing the external magnetic field, the magnetic property of these materials does not remain. The magnetic susceptibility of these materials is negative and very low (about 6-10 - to 3-10 ). All gases (except oxygen), water, silver, gold, copper, diamond, graphite, bismuth, and many organic compounds are (diamagnetic). The magnetic dipoles  in paramagnetic materials do not have a specific and regular orientation; as a result, these materials do not have magnetic properties. If they are placed in a magnetic field,  they become regular along the magnetic field lines. When the magnetic field is removed  , the magnetic dipoles quickly return to the previous state they had in the absence of the field. In this way, paramagnetic materials acquire magnetic properties in strong nanoelectromagnetic fields. The electromagnetic susceptibility of these materials is positive (about 10-6 to 10-1). (Manganese, platinum, aluminum, alkali and  alkaline earth metals, oxygen and nitrogen oxides are nanoparamagnetic  like paramagnetic materials  . Ferromagnetic materials  differ in that a set of magnetic dipoles  are in the same direction and orientation, while these sets themselves  are in different directions and orientations; so that  they neutralize each other's field effect. This set  of magnetic dipoles that are in the same direction is called a nanoelectromagnetic domain. The nanoelectromagnetic property of the particles of these  materials depends on the speed of change of direction of these domains and their orientation in  the direction of the field.

The magnetic property is highly  dependent on the size of the particle. Any magnetic material in bulk  is composed of magnetic domains. Each domain has  thousands of atoms in which the direction of electron spin  is the same and the magnetic moments are oriented parallel  . However, the direction of electron spin in each domain is different from the other domains  . Whenever a large magnetic field aligns all the magnetic domains, a nanoelectromagnetic phase change occurs and magnetization  reaches saturation. Any particle that contains only one domain  can be considered a nanoparticle. Magnetic nanoparticles have  a small number of domains and  are easier to magnetize.

Conclusion :

In ferromagnetic materials, when the particle size  becomes smaller than a single magnetic domain, the phenomenon of  superparamagnetism (the non-attachment of magnetic particles in  nano-size under normal conditions and their high sensitivity to a  magnetic field) occurs. Because nanoparticles  do not require a large force to become magnetized,  they do not deviate much from their natural state and, after becoming magnetized,  do not have much tendency to lose their magnetic properties and return  to their original state.