AD
Abbreviation from the Latin anno domini. Denotes the time period after the birth of Christ.

A/m
Ampère per metre. Unit of magnetisation when expressed per unit of volume. Typically, the natural remanent magnetisation of a baked clay is in the order of 1 A/m and of a sediment 10-3 A/m.

Am2
Ampère times metres squared. Unit of the magnetic moment.

Am2/kg
Ampère times metres squared per kilogram. Unit of magnetisation when expressed per unit of weight.

Anhysteretic remanent magnetisation (ARM)
Remanent magnetisation imparted to a sample in the laboratory by applying a decaying alternating magnetic field in the presence of a steady magnetic field.

Anisotropy of magnetic susceptibility (AMS)
Variation of magnetic susceptibility with direction. Generally, dominated by the form of the ferromagnetic grains and due to an alignment of elongated or flattened grains.

Antiferromagnetism
(see also ferromagnetism). Form of ferromagnetism in crystalline material with two oppositely and equally magnetised sublattices. The quantum mechanical exchange interaction at short distance between cations via an anion (indirect interaction) favours an antiparallel alignment of the individual magnetic moments of atoms or ions. The resulting magnetisation is zero. The magnetic susceptibility is weak. Antiferromagnetics become paramagnetic (see also paramagnetism) beyond the Néel-Temperature. Example: haematite. Antiferromagnetics often have ferromagnetic properties due to impurities (parasitic ferromagnetism, e.g. in goethite, haematite) or because of an imperfect antiparallelism of the magnetic moments (canted antiferromagnetism, e.g. haematite).

Archaeointensity
Estimated intensity of the geomagnetic field in the past, based on measurements of remanent magnetisation of baked clays, that acquire their natural remanent magnetisation as thermoremanent magnetisation. Reheating experiments in a known laboratory field allow to determine absolute values of the ancient  geomagnetic field.



Archaeomagnetic dating
A date obtained by comparing the values of the ancient geomagnetic field elements (declination, inclination, intensity) corresponding to the ChRM of baked clays with standard secular variation diagrams of the local geomagnetic field elements during the past.

Archaeomagnetism
(see also palaeomagnetism) For the archaeologist a dating method based on the remanent magnetisation of baked clays. Study of the magnetic properties of archaeological materials (mainly baked clays) of historical or pre-historical age.

Archaic Period
Cultural period in Greece between 750 and 500 BC, subsequent to the Dark Ages and followed by the Classical period. This period is characterised by the naturalistic representation of the human figure, the formation of city-states and the rise the aristocracy.

Azimuth
Angle between the vertical plane through the observation sight-of-line and the geographic meridial plane.