Which of the following is true about ferromagnetic materials?

Ferromagnetic materials are characterized by their ability to be easily magnetized and to retain their magnetism even after the external magnetic field is removed. This property is due to the alignment of magnetic domains within the material. When a magnetic field is applied, these domains align in the direction of the field, leading to a strong magnetic effect. Once the field is removed, many of these domains remain aligned, allowing the material to retain its magnetization.

This ability to sustain magnetization is what differentiates ferromagnetic materials from other types of magnetic materials. For instance, paramagnetic materials would not retain their magnetism once the external field is removed, and diamagnetic materials do not display any magnetic properties in the presence of an external field.

Understanding the nature of ferromagnetism is essential in various applications, including the manufacturing of permanent magnets and the development of magnetic storage devices. Thus, the correct answer captures the essence of ferromagnetic materials accurately by highlighting both their susceptibility to magnetization and their capacity to hold that magnetism.