How does an electric current make an iron core magnetic?

An electric current makes an iron core magnetic through the process of magnetization, which relies on the alignment of magnetic domains within the material.1

Ferromagnetic materials like iron contain small, naturally magnetized regions called domains that are typically oriented in random directions, resulting in no net magnetic field. When an electric current flows through a coil of wire—such as in a solenoid—it generates an external magnetic field.123

When the iron core is placed within this field, the magnetic domains reorient themselves to align with the direction of the applied field. This alignment significantly increases the magnetic flux density within the iron, as the material's high magnetic permeability allows it to concentrate and amplify the magnetic field produced by the current loops. In a typical electromagnet, this effect is used to create a strong, controllable magnetic force.142