Magnetic Properties of Solids

Magnetic Properties of Solids

• Magnetic materials are capable of being magnetized in a magnetic field and can be classified into three principal groups: diamagnetic, paramagnetic, and ferromagnetic materials.
• Magnetic induction or magnetic flux density (B) refers to the strength and direction of the magnetic field around a magnet or an electric current, and is expressed in units of tesla or weber per square meter.
• The relationship between B and the field strength (H) is given by B = μ₀H, where μ₀ is the permeability of free space.
• In solid materials, the magnetic induction is given by B = μH, where μ is the permeability of the solid material.

Classification of Magnetic Materials

• Diamagnetic materials are weakly repelled by magnetic fields and include examples such as gold and lead.
• Paramagnetic materials are weakly attracted by magnetic fields and include examples such as chromium and aluminum.
• Ferromagnetic materials are strongly attracted by magnetic fields and include examples such as cobalt, nickel, and gadolinium.
• Antiferromagnetic materials have a net magnetic moment of zero due to the compensation of parallel and antiparallel magnetic dipoles, and include examples such as nickel oxide and manganese oxide.
• Ferrimagnetic materials have a small net magnetic moment due to the unequal arrangement of parallel and antiparallel magnetic dipoles, and include examples such as magnetite (Fe₃O₄).

Hysteresis Loop and Measurement of Magnetic Properties

• The hysteresis loop represents the relation between the magnetization of a material and the applied magnetic field.
• Magnetic properties can be measured using the magnetization curve, which represents the relation between the magnetization of a material and the applied magnetic field.

Magnetic Properties vs Temperature

• The magnetization of a material (M) is given by the Curie-Weiss law: M = C x (B / T), where C is the Curie constant, B is the applied magnetic field, and T is the temperature.
• The magnetic susceptibility (X) is given by X = M / H, where H is the field strength.

Soft Magnetic Materials

• Soft magnetic materials have high permeability, low coercivity, and low residual magnetism, making them suitable for alternating current (AC) applications.
• Applications of soft magnetic materials include transformers, inductors, and energy storage devices.

Ferrites

• Ferrites are magnetic oxides in which ferric ions play a prominent role in their composition.
• Ferrites have specific properties, including suitable saturation magnetization, high electrical resistivity, and excellent chemical and thermal stability.
• Ferrites consist of iron oxide as the main component and metal oxides.

Types of Ferrites

• Spinel ferrites have a face-centered cubic (FCC) structure and are used in transformer cores and sensing elements.
• Garnet ferrites have a general formula R₃Fe₂O12, where R is a trivalent rare earth ion, and are used in microwave devices and laser technology.
• Ortho-ferrites have a general formula MeFeO3, where Me is a large trivalent metal ion, and show a weak ferromagnetism.
• Hexagonal ferrites crystallize in a hexagonal structure and are classified into five types: M, Y, Z, U, and W.

Neel Temperature

• The Neel temperature is the temperature above which anti-ferromagnetic materials become paramagnetic.