Origin of VRM
See also: SuperparamagnetismViscous remanent magnetization is the result of jumps between magnetic states driven by thermal fluctuations. In the simplest case, there is a single characteristic time τ called the thermal relaxation time. If the starting magnetization is M0 and the magnetization in equilibrium is Meq, the magnetization after a time t is
If M0 is a natural remanent magnetization (NRM) acquired in the Earth's field at one time, and Meq is the equilibrium magnetization in a different field at some later time, the change in remanence M(t) -M0 is the VRM.
The above equation is applicable to the simplest single domain magnets, those described by the Stoner–Wohlfarth model. The relaxation time τ depends on factors such as the size of the magnet and its magnetic anisotropy. Rocks have collections of magnetic minerals with varying size and anisotropy, and therefore a broad spectrum of relaxation times. The magnetization tends to have a logarithmic dependence on time, so the rate of change is often represented by a viscosity coefficient
Read more about this topic: Viscous Remanent Magnetization
Famous quotes containing the words origin of and/or origin:
“The origin of storms is not in clouds,
our lightning strikes when the earth rises,
spillways free authentic power:
dead John Brown’s body walking from a tunnel
to break the armored and concluded mind.”
—Muriel Rukeyser (1913–1980)
“Good resolutions are useless attempts to interfere with scientific laws. Their origin is pure vanity. Their result is absolutely nil. They give us, now and then, some of those luxurious sterile emotions that have a certain charm for the weak.... They are simply cheques that men draw on a bank where they have no account.”
—Oscar Wilde (1854–1900)