Ferromagnetic substances are materials that can be magnetized and retain their magnetic properties even after an external magnetic field is removed. Common examples include iron, nickel, and cobalt. These materials have regions called magnetic domains, where the magnetic moments of atoms align in the same direction, contributing to their overall magnetism. When exposed to a magnetic field, the domains in ferromagnetic substances can become aligned, enhancing their magnetic strength. This property makes them useful in various applications, such as in electromagnets, transformers, and permanent magnets. Their ability to be magnetized and demagnetized is crucial in many technological devices.