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Questions and Answers
What is the range of coercivity of magnetic materials mentioned in the content?
What is the range of coercivity of magnetic materials mentioned in the content?
- 1 A m−1 to 10 A m−1
- Less than 1 A m−1 to 5 MA m−1
- 0.1 A m−1 to 1 MA m− (correct)
- Less than 0.1 A m−1 to more than 10 MA m−1
The hardness of magnetic materials has decreased over the twentieth century.
The hardness of magnetic materials has decreased over the twentieth century.
False (B)
What does time reversal symmetry indicate about magnetization distribution?
What does time reversal symmetry indicate about magnetization distribution?
A state with a certain magnetization distribution should have the same energy as the state with reversed magnetization.
The natural direction of magnetization in a ferromagnetic domain is usually constrained to lie along one or more _____ axes.
The natural direction of magnetization in a ferromagnetic domain is usually constrained to lie along one or more _____ axes.
Match the types of magnetic materials with their properties:
Match the types of magnetic materials with their properties:
Flashcards
Coercivity
Coercivity
The range of magnetic strength in a material, from weak to strong.
Easy Axis
Easy Axis
The direction within a magnetic material where it's easiest to magnetize.
Ferromagnetic Domain
Ferromagnetic Domain
The natural state of a ferromagnetic material, where numerous small magnetic domains exist within it.
Remanence
Remanence
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Anisotropy
Anisotropy
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Study Notes
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 (Tsc) 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, TN)
- 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.
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