Glossary of Paleomagnetic and Rock Magnetic Acronyms - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 137

fi eld for that latitude. The EI pair used for the inclina-
tion correction is derived from the secular variation
behavior of the present geomagnetic fi eld over the
past 5 million years.
FMR, ferromagnetic resonance: An electron spin reso-
nance spectroscopic technique used to understand
the magnetic structure of ferromagnetic materials,
including the magnetic anisotropy of individual par-
ticles and magnetostatic interactions between mag-
netic particles.
FORC, fi rst - order reversal curve: A curve that results
from a complicated procedure that includes contour-
ing of multiple hysteresis loops with decreasing
peak fi elds from magnetic saturation down to nearly
0, and changing the coordinate system from that
used for the generation of the hysteresis loops.
The FORC diagram that results can be used to
measure the coercivity of the collection of magnetic
grains in a sample as well as the importance of mag-
netic interactions between the magnetic sample
grains.
GAD, geomagnetic axial dipole: The geometric con-
fi guration of the Earth's magnetic fi eld when secu-
lar variation has been time averaged. This is the
fi eld that results from a magnetic dipole at the
center of the Earth that is parallel to the Earth's
rotational axis.
IRM, isothermal remanent magnetization: The mag-
netization that results from the application of a DC
magnetic fi eld to a sample.
J sat , saturation magnetization: This measurement results
from a hysteresis loop measurement and is the great-
est magnetization acquired by a sample in the pres-
ence of the magnetic fi eld causing it.
J rs , saturation remanence, also known as a SIRM: This
is the greatest magnetization acquired by a sample
after it has reached J sat , but it is measured when the
fi eld that caused it has been turned off.
MTM, multi - taper method: A modifi cation of Fourier
spectral analysis in which multiple spectral esti-
mates are calculated from the same sample, each
time the data series being multiplied by a different
orthogonal taper function. The technique was devel-
oped by DJ Thomson.
NRM, natural remanent magnetization: A blanket
term used to indicate all remanent magnetizations
that are naturally acquired by a rock. It usually
refers to the magnetization measured before a rock
sample is demagnetized or before it has had a labora-
tory remanence applied to it.

OAI, oxic - anoxic interface: The boundary between the
oxygen-rich and oxygen-free depths, either in the
water column or in the sediment column.
pDRM, post - depositional remanent magnetization:
The DRM that a sediment acquires at some point
after deposition. It is usually acquired within the top
10-20 cm of the sediment column, if it occurs at all.
PSD, pseudo - single domain: A small, multi - domain
ferromagnetic grain that behaves like a single-
domain grain. It is usually envisioned as containing
just a few domains (regions of uniform magnetiza-
tion), but PSD behavior could also be due to non-
uniform magnetization confi gurations (vortex or
fl ower) as indicated by micro-magnetic modeling.
PSV, paleosecular variation: The directional and inten-
sity changes in the local geomagnetic fi eld vector
caused by the dynamic behavior of the Earth's mag-
netic fi eld on timescales of hundreds-thousands of
years. The dynamic behavior includes wobbling of
the main dipole ( c. 90% of the fi eld) around the
Earth's rotational axis, the growth and decay in the
strength of the dipole, the movement of the non-
dipole fi eld foci (where fi eld lines project in and out
of the Earth) and the growth and decay of the non-
dipole foci. The non - dipole fi eld foci are like small N
and S poles in the Earth's fi eld after the main dipole
has been mathematically subtracted. Their occur-
rence causes the geomagnetic fi eld to deviate from a
simple dipole in confi guration.
SIRM, saturation isothermal remanent magneti-
zation: The isothermal remanence acquired by a
sample after it has been exposed to a saturating DC
fi eld. See J rs above.
χ , susceptibility: The proportionality constant between
the induced magnetization and the fi eld that is
inducing it ( J = χ H ). For AMS, the susceptibility is
described by a second-rank tensor (3 × 3 matrix).
χ fd , frequency - dependent susceptibility: In a labora-
tory measurement of susceptibility, the inducing
fi eld used ( H ) is an alternating fi eld so that no VRM
is induced in the sample during the measurement.
For χ fd the susceptibility is measured in alternating
fi elds with different frequencies, usually an order of
magnitude or greater different. If the susceptibility
varies greatly with frequency, it is a measure of
superparamagnetic grains in a sample.
χ ARM , ARM susceptibility: In this case not the suscep-
tibility that causes an induced magnetization, but
the ARM acquired as a function of the DC magnetic
fi eld used for the application of the ARM. Usually it