Magnetic Materials: Properties and Applications

Magnetic Materials: Properties and Applications

• Coercivity of magnetic materials greatly expanded in the 20th century, ranging from less than 0.1 A m⁻¹ to over 10 MA m⁻¹. (Figure 1.5)
• Natural magnetization in ferromagnetic domains aligns along easy axes. This is due to circulating electron currents, and reversing magnetization has equal energy.
• Materials with no magnetic ordering can be paramagnetic or diamagnetic.
  • Paramagnetic materials have induced magnetization in the same direction as the applied field (H)
  • Diamagnetic materials have induced magnetization in the opposite direction.
  • Superconductors exhibit diamagnetic hysteresis loops below the superconducting transition temperature (T_sc) and their susceptibility can approach -1.
  • Susceptibility (χ) of paramagnetic materials often follows the Curie law (χ = C/T), but some metallic paramagnets and diamagnets have a temperature-independent susceptibility.
• Ferromagnetism arises from alignment of atomic magnetic moments.
• Antiferromagnetism involves two oppositely oriented magnetic sublattices with a net magnetization of zero, but a phase transition (Néel temperature, T_N)
• A metamagnetic transition can change an antiferromagnet to a ferromagnet in high fields.
• The global magnetic materials market is valued over $30 billion annually.
• Magnetic materials are crucial in diverse applications like recording media, sensors, and motors.
• Magnetic materials are part of consumer electronics, audio equipment, telecommunications, medical imaging, and computers.
• The composition of Earth's crust and whole Earth show significant iron & other magnetic elements (Figure 1), with Earth's crust having a higher proportion of oxygen
• Technological advancements in magnetic materials (coercivity, miniaturization) have led to exponential improvements in recording and other applications.
• Soft magnetic material core losses halved every 18 years throughout the 20th century (Figure 1.12)
• Maximum available susceptibilities doubled every 6 years in first half of the 20th century
• Further susceptibility improvements seem less crucial, but improvements in temporary magnets at frequencies above 1 MHz are needed.

Explore the fascinating world of magnetic materials with this quiz. Delve into the properties of ferromagnetic, paramagnetic, and diamagnetic materials, and understand their applications in modern technology. Test your knowledge on coercivity, magnetization, and superconductors.