1-2: Basic Principles of Magnetism Flashcards
(34 cards)
What defines diamagnetic behavior?
Spin and orbital moments cancel – no net moment
What defines paramagnetic behavior?
Possesses spin magnetic moment as well as orbital magnetic moment, only partial cancellation.
What occurs to a paramagnetic material with increasing temperature?
Magnetisation decreases as temperature increases
What defines ferromagnetic behavior?
Spin and orbital moments do not cancel, exchange coupling occurs
What is exchange coupling in terms of magnetism?
Adjacent atoms are close in crystal lattice so electron orbitals overlap and strong interaction occurs.
What is the arrangement of ferromagnetic behavior?
Regular arrows in a parallel direction, all same length.
What is the arrangement of antiferromagnetism?
Atoms have same strength but neighboring atoms have oppositely directed moments – zero net magnetisation.
When does net magnetism occur in antiferromagnetic materials?
If there is damage or deficit to crystal lattice
What is the arrangement of ferrimagnetic behavior?
Opposing directions, but different strengths so there is a net magnetic direction.
Give an example of a ferrimagnetic mineral, and its chemical composition.
Magnetite, Fe3O4.
What is “canted” antiferromagnetism?
When the directions are equal and opposite, but slightly turned in on direction or the next, such as /\/\/ all pointing right.
Give an example of a canted antiferromagnetic mineral, and its chemical composition.
Haematite, Fe2O3
Why are paramagnets so un-magnetic at room temperature?
Thermal energy at room temperature disrupts alignment thousands of times more than magnetic energy trying to align the moments.
Paramagnets need either ___ or ____ to be magnetized.
Very low temperatures or very high magnetic fields
What would the graph for M vs H look like for a paramagnet?
Linear and close to the origin
What happens when the external field is removed from diamagnets and paramagnets?
Magnetisation disappears
What happens to a ferromagnetic material when a sample is saturated, and then the field is reduced back to zero?
The sample is left with a permanent magnetization, called saturated magnetic remanence.
What happens when a negative field is implemented on a sample with magnetic remanence?
It can become negatively saturated.
The act of saturating a ferromagnet in one direction, and then the opposite creates a ___ ___.
Hysteresis Loop
What is the difference between remanence and saturation remanence?
Remanence occurs when the sample has been magnetically reversed before reaching saturation, saturation remanence is therefore the maximum amount of remanence the sample can hold.
How do you spell the R from SIRM?
REM-AN-ENCE
What is the coercive force?
Hc, the point where a sample with saturation remanence has been reversed to the point where M = 0.
How does one return the sample to the origin where H = 0 and M = 0?
Apply coercivity of remanence (Hcr) – a negative magnetic field of Hcr must be applied, where at the point of Hcr, if a positive field was applied, the sample would pass back through the origin.
Why is Mrs always smaller than Ms?
The ferromagnet is divided into small regions where magnetisation is uniform within the region, but the vector of each region differs from its neighbor.
