Magnetic declination is the angle on the horizontal plane between magnetic north and true (geographical) north. It varies depending on the observer's position on the Earth's surface and changes over time due to the movement of the Earth's magnetic poles. It is a critical factor for navigation using a magnetic compass.

The domain theory of magnetism explains the behavior of ferromagnetic materials. Ferromagnetic substances, such as iron, nickel, and cobalt, contain microscopic regions called magnetic domains where atomic magnetic moments are aligned. When an external magnetic field is applied, these domains align to produce a strong magnetic effect. Aluminium, copper, and silver are paramagnetic or diamagnetic and do not exhibit this domain structure.

Paramagnetic substances are weakly attracted by an external magnetic field. Platinum is a well-known paramagnetic material, whereas nickel is ferromagnetic, and hydrogen and silver are generally diamagnetic.

Hammering a ferromagnetic rod while it is aligned with an external magnetic field, such as the Earth's magnetic field, can induce magnetism by aligning the magnetic domains. Conversely, hammering a rod perpendicular to the field lines can demagnetize it. While passing a direct current through a coil surrounding a material is a common way to create an electromagnet, the specific method of mechanical agitation like hammering is a recognized, albeit less efficient, technique for inducing magnetism.

The Curie temperature is the critical temperature above which a ferromagnetic material loses its permanent magnetic properties and transitions into a paramagnetic state. This phase transition occurs because thermal agitation becomes strong enough to overcome the exchange interactions that align electron spins, resulting in the loss of long-range magnetic order.

The Curie temperature is the critical temperature above which a ferromagnetic material loses its spontaneous magnetization and transitions into a paramagnetic state. In this state, the material's magnetic dipoles become randomly oriented due to thermal agitation.

Mercury is classified as a diamagnetic substance. Diamagnetic materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, causing them to be weakly repelled by magnets. This behavior is a fundamental property of mercury's electronic configuration.

Diamagnetic materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, resulting in a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted to magnets. Thus, only diamagnetic substances exhibit repulsion.

The Curie-Weiss law describes the magnetic susceptibility of a ferromagnetic material in the paramagnetic region. For iron, this law is obeyed only at temperatures above its Curie temperature, where the material transitions from a ferromagnetic state to a paramagnetic state.

The coercive force, or coercivity, is the intensity of the reverse magnetic field required to reduce the magnetization of a ferromagnetic material to zero after it has been saturated. Essentially, it represents the material's resistance to becoming demagnetized, meaning it opposes the process of demagnetization.