Magnetization increases with temperature for antiferromagnetic nanoparticles.
This odd experimental finding, made a few years ago, is now explained,
for the first time, by physicists at the Technical University of Denmark.
The experimental behavior is odd for two reasons: first because antiferromagnets,
whose tiny neighboring magnetic moments generally line up in an alternating
down and up pattern, are supposed to sustain no significant net magnetization
of their own in an applied field; and second because magnetism itself,
which arises at the microscopic level from the aligned magnetic moments
of many atoms (the atoms act as tiny bar magnets), should tend to decline
as the disruptive action of higher temperatures takes effect.
The Danish physicists explain why "thermoinduced magnetization" is
missing in bulk antiferromagnetic samples (which accounts for their
being nonmagnetic), but become more noticeable in dots with size below
10 nm. Steen Morup (firstname.lastname@example.org) and Cathrine Frandsen (email@example.com)
argue that antiferromagnetic nanoparticles might be engineered into
a new class of material, one in which magnetization can be switched
quickly and without energy loss, making it valuable for use in high-frequency
electronic devices. (Morup
and Frandsen, Physical Review Letters, 28 May 2004.)