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382: Environmental Magnetism > Magnetic Parameters and Their Applications > Flashcards

Magnetic Parameters and Their Applications Flashcards

1
Q

What are the units of Magnetic field?

A

Tesla (usually miliTesla, mT)

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2
Q

What are the units of Magnetization?

A

Am2/kg

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3
Q

What are the units of volume susceptibility?

A

Dimensionless

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4
Q

What is the equation for volume susceptibility?

A

κ = M/H

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5
Q

How do we obtain mass susceptibility from volume susceptibility?

A

χ = κ/ρ

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6
Q

What are the units of mass susceptibility?

A

m3/kg

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7
Q

What defines a low magnetic field?

A

Less than ~10^3 A/m

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8
Q

What does SIRM or Ms show?

A

The abundance of remanence carrying minerals

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9
Q

What does χ or κ show?

A

The abundance of all magnetic minerals

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10
Q

On the graph M vs H, what does a steeper paramagnetic slope imply?

A

Increasing susceptibility

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11
Q

χ of mineral A:____ is greater than χ of mineral B:____.

A

Magnetite > haematite

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12
Q

χ of ____ behaving materials is greater than the χ of ____ behaving minerals.

A

Paramagnetic > diamagnetic

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13
Q

χ only measures magnetite abundance if ___ or ___.

A

Paramagnetic/diamagnetic/haematite mineral content is similar or if magnetite grain size doesn’t vary greatly

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14
Q

What does SIRM stand for?

A

Saturation Isothermal Remnant Magnetisation

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15
Q

What does IRM0-20mT mean?

A

The amount of remanence left after the sample has been exposed to a magnetic field of between 0-20mT

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16
Q

What does bIRM60mT mean?

A

The remanence of a sample after it has been exposed to a backfield of 60mT

17
Q

Compare the susceptibility of a small magnetite grain to a large magnetite grain

A

Small grains more difficult to magnetize, will have a lower susceptibility

18
Q

What comes from subtracting low-frequency susceptibility from high-frequency susceptibility?

A

Susceptibility of ferrimagnetic minerals

19
Q

What does %χfd indicate?

A

The abundance of super-paramagnetic grains

20
Q

What is a typical high value for %χfd indicate, and what does this mean?

A

A typical high value can be around 15-20%, indicating abundance of SP grains

21
Q

What does %IRM20mT mean?

A

The amount of magnetic remanence once a sample has been charged to 20mT, as a % of the saturated remanence for the sample.

22
Q

What does a high value of IRM20mT and IRM50mT generally imply and why?

A

Abundance of coarse grained magnetite grains as larger magnetite grains are easier to magnetize (only requires small magnetisation)

23
Q

What does a high value of IRM0.3-1T generally imply and why?

A

Abundance of haematite or goethite, as they require large magnetisation for any remanence.

24
Q

If magnetite dominates the sample, what does a high value of IRM100mT generally imply and why?

A

Large magnetite grain sizes, as there is a lot of remanence at a relatively small magnetization

25
Q

What is another way of expressing HIRM?

A

IRM0.3-1T

26
Q

What is the process for obtaining a value for ARM?

A

Sample placed in a steady DC field, then exposed to alternating current AC reduced to 0

27
Q

What is χARM?

A

Susceptibility of ARM per unit of DC field

28
Q

What does a high value of χARM indicate?

A

More grains near the SP/SD boundary – smaller grains better at acquiring ARM

29
Q

What is the typical grain size of the SP/SD boundary?

A

~0.03um

30
Q

What does sigma mean in terms of environmental magnetism?

A

per kg of dry mass

31
Q

Larger magnetite particles are saturated by __mT

A

100mT

32
Q

What is the highest value of σIRM100mT/σSIRM3T, and what does that mean?

A

1, which indicates the sample is close to saturation at 100mT, indicating large magnetite grains

33
Q

What does a low value of σIRM100mT/σSIRM3T mean?

A

More haematite/goethite

34
Q

What does a high value of ARM/SIRM imply?

A

The sample contains more particles with SD-PSD grain size.

35
Q

What mT defines a low frequency magnetisation?

A

LF < 1mT

36
Q

What mT defines a high frequency magnetisation?

A

HF > 100mT

37
Q

What contribution does a high frequency magnetisation account for?

A

Paramagnetic and antiferromagnetic contribution

382: Environmental Magnetism (7 decks)

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