Which statement is true about ferromagnetic materials?

Which statement is true about ferromagnetic materials?

• A. They can become permanent magnets after exposure to a strong field
• B. They cannot be magnetized
• C. They are only magnetic at very low temperatures
• D. They respond only to electric fields

Answer: (A)

Ferromagnetic materials have magnetic domains, tiny regions where spins align. When you expose such a material to a strong external magnetic field, these domains reorient so that more of them point in the same direction, producing a net magnetization. Even after you remove the field, many of those aligned domains stay that way because the interactions between neighboring spins favor parallel alignment. That persistence of magnetization is what lets ferromagnets become permanent magnets after a strong field is applied. These properties explain why the statement is true: a strong field can organize the domains so the material remains magnetized once the field is gone. By contrast, the other ideas don’t fit. Ferromagnets can be magnetized (so they aren’t incapable of magnetization), and they’re magnetic below the Curie temperature—not only at extremely low temperatures. They respond to magnetic fields, not exclusively to electric fields.

Ferromagnetic materials have magnetic domains, tiny regions where spins align. When you expose such a material to a strong external magnetic field, these domains reorient so that more of them point in the same direction, producing a net magnetization. Even after you remove the field, many of those aligned domains stay that way because the interactions between neighboring spins favor parallel alignment. That persistence of magnetization is what lets ferromagnets become permanent magnets after a strong field is applied.

These properties explain why the statement is true: a strong field can organize the domains so the material remains magnetized once the field is gone. By contrast, the other ideas don’t fit. Ferromagnets can be magnetized (so they aren’t incapable of magnetization), and they’re magnetic below the Curie temperature—not only at extremely low temperatures. They respond to magnetic fields, not exclusively to electric fields.