Magnetic Parameters and Their Applications Flashcards
What are the units of Magnetic field?
Tesla (usually miliTesla, mT)
What are the units of Magnetization?
Am2/kg
What are the units of volume susceptibility?
Dimensionless
What is the equation for volume susceptibility?
κ = M/H
How do we obtain mass susceptibility from volume susceptibility?
χ = κ/ρ
What are the units of mass susceptibility?
m3/kg
What defines a low magnetic field?
Less than ~10^3 A/m
What does SIRM or Ms show?
The abundance of remanence carrying minerals
What does χ or κ show?
The abundance of all magnetic minerals
On the graph M vs H, what does a steeper paramagnetic slope imply?
Increasing susceptibility
χ of mineral A:____ is greater than χ of mineral B:____.
Magnetite > haematite
χ of ____ behaving materials is greater than the χ of ____ behaving minerals.
Paramagnetic > diamagnetic
χ only measures magnetite abundance if ___ or ___.
Paramagnetic/diamagnetic/haematite mineral content is similar or if magnetite grain size doesn’t vary greatly
What does SIRM stand for?
Saturation Isothermal Remnant Magnetisation
What does IRM0-20mT mean?
The amount of remanence left after the sample has been exposed to a magnetic field of between 0-20mT
What does bIRM60mT mean?
The remanence of a sample after it has been exposed to a backfield of 60mT
Compare the susceptibility of a small magnetite grain to a large magnetite grain
Small grains more difficult to magnetize, will have a lower susceptibility
What comes from subtracting low-frequency susceptibility from high-frequency susceptibility?
Susceptibility of ferrimagnetic minerals
What does %χfd indicate?
The abundance of super-paramagnetic grains
What is a typical high value for %χfd indicate, and what does this mean?
A typical high value can be around 15-20%, indicating abundance of SP grains
What does %IRM20mT mean?
The amount of magnetic remanence once a sample has been charged to 20mT, as a % of the saturated remanence for the sample.
What does a high value of IRM20mT and IRM50mT generally imply and why?
Abundance of coarse grained magnetite grains as larger magnetite grains are easier to magnetize (only requires small magnetisation)
What does a high value of IRM0.3-1T generally imply and why?
Abundance of haematite or goethite, as they require large magnetisation for any remanence.
If magnetite dominates the sample, what does a high value of IRM100mT generally imply and why?
Large magnetite grain sizes, as there is a lot of remanence at a relatively small magnetization
What is another way of expressing HIRM?
IRM0.3-1T
What is the process for obtaining a value for ARM?
Sample placed in a steady DC field, then exposed to alternating current AC reduced to 0
What is χARM?
Susceptibility of ARM per unit of DC field
What does a high value of χARM indicate?
More grains near the SP/SD boundary – smaller grains better at acquiring ARM
What is the typical grain size of the SP/SD boundary?
~0.03um
What does sigma mean in terms of environmental magnetism?
per kg of dry mass
Larger magnetite particles are saturated by __mT
100mT
What is the highest value of σIRM100mT/σSIRM3T, and what does that mean?
1, which indicates the sample is close to saturation at 100mT, indicating large magnetite grains
What does a low value of σIRM100mT/σSIRM3T mean?
More haematite/goethite
What does a high value of ARM/SIRM imply?
The sample contains more particles with SD-PSD grain size.
What mT defines a low frequency magnetisation?
LF < 1mT
What mT defines a high frequency magnetisation?
HF > 100mT
What contribution does a high frequency magnetisation account for?
Paramagnetic and antiferromagnetic contribution
