The smallest known permanent magnets in a metal showing magnetic characteristics are called:

The smallest known permanent magnets in a metal exhibiting magnetic characteristics are referred to as domains. These domains are regions within a material where a group of atoms is uniformly aligned in their magnetic orientations, which contributes to the overall magnetic properties of the material. In ferromagnetic materials, these domains can either align themselves in the same direction when subjected to an external magnetic field, enhancing the material's magnetism, or can remain randomly oriented, resulting in no net magnetization when the material is not magnetized.

In summary, understanding domains is crucial in the context of magnetic materials and their uses, especially in applications involving eddy current testing, as the interaction between eddy currents and magnetic properties can affect test results significantly. This concept applies to various fields, including materials science and engineering.