Lecture 13: Magnetic Properties

Question 1

Describe what a Bohr Magneton represents

Answer 1

A Bohr Magneton is a physical constant that quantifies the magnetic moment typical of an electron due to its orbital or spin angular momentum.

Question 2

What is ferromagnetism?

Answer 2

Ferromagnetism is a type of magnetism where magnetic moments of atoms align parallel to each other within a material, creating strong internal magnetization.

Question 3

Explain the concept of antiferromagnetism.

Answer 3

Antiferromagnetism is a type of magnetism in which adjacent ions align themselves with opposite spins, resulting in no net magnetic moment at a macroscopic scale.

Question 4

What is ferrimagnetism?

Answer 4

Ferrimagnetism occurs when magnetic moments of adjacent atoms align in opposite directions, but in unequal strengths, causing a net magnetic moment.

Question 5

Define helimagnetism.

Answer 5

Helimagnetism is a type of magnetic ordering where spins on adjacent atoms twist around the axis moving through the crystal instead of aligning straight.

Question 6

What is a spin glass state?

Answer 6

A spin glass state is a magnetic state characterized by disordered magnetic moments that are frozen into place upon cooling, without long-range magnetic order.

Question 7

How does Lenz’s Law relate to diamagnetism?

Answer 7

Lenz’s Law in diamagnetism describes how induced magnetic fields in a material oppose the change in the external magnetic field that induced them.

Question 8

What is magnetic flux density?

Answer 8

Magnetic flux density, represented as B, is the measure of the magnetic field’s strength within a medium.

Question 9

What does magnetization (M) indicate about a material?

Answer 9

Magnetization indicates the degree to which a material becomes magnetized when placed in an external magnetic field and is defined as the net magnetic moment per unit volume.

Question 10

Define magnetic susceptibility.

Answer 10

Magnetic susceptibility is a dimensionless proportionality constant that indicates how much a material will become magnetized in an external magnetic field.

Question 11

What is the Curie Law?

Answer 11

The Curie Law states that the magnetic susceptibility of a paramagnetic material is inversely proportional to its temperature.

Question 12

Describe the Curie-Weiss Law.

Answer 12

The Curie-Weiss Law modifies the Curie Law by incorporating a temperature offset known as the Weiss constant, reflecting interactions between spins.

Question 13

What is the significance of the Neel temperature?

Answer 13

The Neel temperature is the temperature below which an antiferromagnetic material transitions to a paramagnetic state.

Question 14

Explain what is meant by Pauli paramagnetism.

Answer 14

Pauli paramagnetism is a type of magnetism exhibited by conduction electrons in metals that are influenced by Pauli’s exclusion principle.

Question 15

How does the 4d band relate to ferromagnetism in transition metals?

Answer 15

In transition metals, the density of states at the Fermi level within the 4d band must be high for ferromagnetism to occur, as this enhances the exchange interactions leading to parallel spin alignment.

Question 16

What is ferromagnetic exchange coupling?

Answer 16

Ferromagnetic exchange coupling is the interaction that causes atomic magnetic moments in ferromagnetic material to align parallel to each other.

Question 17

Describe ferromagnetic domains.

Answer 17

Ferromagnetic domains are regions within a ferromagnetic material where the magnetic moments are uniformly aligned; the direction of alignment varies from one domain to another.

Question 18

What is magnetic hysteresis?

Answer 18

Magnetic hysteresis is the lagging of magnetization behind the magnetizing force, typically illustrated with a hysteresis loop graph showing the relationship between applied magnetic field and magnetization.

Question 19

Define coercive force.

Answer 19

Coercive force is the intensity of the applied magnetic field required to reduce the magnetization of a ferromagnetic material to zero after achieving saturation.

Question 20

What is the difference between soft and hard magnetic materials?

Answer 20

Soft magnetic materials have low coercivity and are easy to magnetize and demagnetize, while hard magnetic materials have high coercivity and retain their magnetism.

Question 21

What are rare earth magnets and why are they important?

Answer 21

Rare earth magnets are strong permanent magnets made from alloys of rare earth elements. They are important due to their ability to provide significant magnetic strength in compact sizes, crucial for various modern technologies.

Question 22

Explain the role of giant magnetoresistance (GMR) in technology.

Answer 22

Giant magnetoresistance is a quantum mechanical magnetoresistance effect observed in thin film structures composed of alternating ferromagnetic and non-magnetic layers. GMR is crucial for developing sensitive read heads in modern hard disk drives.

Question 23

What is a magnetic dipole?

Answer 23

A magnetic dipole consists of two magnetic poles, north and south, separated by a distance but linked by magnetic lines of force.

Question 24

Define magnetic moment.

Answer 24

Magnetic moment is a vector quantity that represents the magnetic strength and orientation of a magnet or other object that produces a magnetic field.

Question 25

What units are used to measure the magnetic field?

Answer 25

The magnetic field is measured in Amperes per meter (A/m) in the SI unit system.

Question 26

What is spintronics?

Answer 26

Spintronics is a technology that exploits both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.

Question 27

Explain the Pauli Exclusion Principle in the context of magnetic properties.

Answer 27

The Pauli Exclusion Principle states that no two electrons can occupy the same quantum state simultaneously, influencing magnetic properties by dictating electron pairing and spin orientations.

Question 28

What is diamagnetism?

Answer 28

Diamagnetism is a form of magnetism that occurs in materials where all the electrons are paired, and there is no net magnetic moment; such materials are repelled by a magnetic field.

Question 29

Define paramagnetism.

Answer 29

Paramagnetism occurs in materials that have unpaired electrons and weakly attract to external magnetic fields.