Magnet
Rare earth (lanthanoid) elements have a partially occupied "f" electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets.
Terahertz metamaterial
The development of electromagnetic, artificial-lattice structured materials, termed metamaterials, has led to the realization of phenomena that cannot be obtained with natural materials. This is observed, for example, with a natural glass lens, which interacts with light (the electromagnetic wave) in a way that appears to be one-handed, while light is delivered in a two-handed manner. In other words, light consists of an electric field and magnetic field. The interaction of a conventional lens, or other natural materials, with light is heavily dominated by the interaction with the electric field (one-handed). The magnetic interaction in lens material is essentially nil. This results in common optical limitations such as a diffraction barrier. Moreover, there is a fundamental lack of natural materials that strongly interact with light's magnetic field. Metamaterials, a synthetic composite structure, overcomes this limitation. In addition, the choice of interactions can be invented and re-invented during fabrication, within the laws of physics. Hence, the capabilities of interaction with the electromagnetic spectrum, which is light, are broadened.