09 - Magnetic properties Flashcards
two main ffects due to magnetic field
- induced magnetization
2. remanent magnetization
- induced magnetization
magnetic field is applied to a material with a magnetic susceptibility
- remanent magnetization
exists regardless of field
occurs within ferri & ferromagnetic substances
- induced magnetization
volume susceptibility kappa
kappa = material magnetization M / magnetic field strength H
- induced magnetization
mass susceptibility kappa_g
kappa_g = kappa / rho
Magnetic induction
B = mü0müH
B = mü0 * (H+M)
B = mü0 * (1+k) * H
Diamagnetism
create magnetic field in opposition to external field
only in applied field!
low neg. magn. susceptibility
Diamagnetic minerals
Calcite, Dolomite
Quartz
Fluorite, Halite, Anhydrite
Orthoclase
Paramagnetic
create magnetic field in direction of external field
only in applied field!
pos. susceptibility (10^-4 - 10^-2)
inversely propertional to abs. T
Paramagnetic
minerals
Olivine, Amphibole, Pyroxene
Micas, Illite Chlorite
Dolomite
Ferro-, Antiferro-, and Ferrimagnetic Materials
Ferro AAAAA - parallel
Ferri AvAvA - antiparallel intrinsic moments
Aniferro AVAVAV - equal but antiparallel
high pos. susceptibility
remanent magnetization
Ferro-, Antiferro-, and Ferrimagnetic Materials
dependencies
- temperature
T higher than T_c: Paramagnetic properties M = Mi + Mr - field strength
- magnetic history (hysteresis loop)
Ferro-, Antiferro-, and Ferrimagnetic Materials
Koenigsberger Q ratio
Q= Mr/Mi= Mr / (kappa*H)
induced magnetization Mi
remanet magnetization Mr
Ferro-, Antiferro-, and Ferrimagnetic Materials
minerals
Titanomagnetites (igneous)
Magnetite (igneous, metamorphic, sedimentary)
Hematite (sediments,igneous)
Ilmenite (metamorphic)
Pseutobrookite (igneous metamorphic)
Pyrrhotite
Goethite
Magnetic properties depend on
chemical inhomogeneity
depositional
crystallization
post formational conditions
ferrimagnetic minerals
Susceptibility
Sediments
Granites gneisses
intrusive basic rocks
Sediments:
kappa <10^-4
Granites gneisses:
kappa = 10^-4 - 10^-3
intrusive basic rocks:
kappa >10^-3
TRM
Thermoremanent magnetization
remanence acquired by a rock, when it is cooled from T above T_c to lower T
Q > 1
CRM
Chemical remanent magnetization
during formation of magnetic mineral
related to processes
such as oxidation, dehydration, precipitation, recrystallization
DRM
Detrital/ Depositional remanent magnetization
oriented deposition of previously magnetized mineral grains
depend on depositional env. (low turbuleces) & sediment type (clays)
marine sediments, lake, varved clays
(post-depositional remanent magnetization PDRM)
