...
Two
...
Paradigms
...
of
...
Magnetism
...
Magnetism
...
is
...
a
...
macroscopic
...
phenomenon
...
with
...
its
...
origin
...
deeply
...
rooted
...
in
...
quantum
...
mechanics.
...
In
...
condensed
...
matter
...
physics,
...
there
...
are
...
two
...
paradigms
...
for
...
magnetism:
...
localized
...
spins
...
interacting
...
via
...
tunnelling,
...
and
...
delocalized
...
spins
...
interacting
...
via
...
an
...
exchange
...
energy.
...
The
...
latter
...
gives
...
rise
...
to
...
itinerant
...
ferromagnetism
...
which
...
is
...
responsible
...
for
...
the
...
properties
...
of
...
transition
...
metals
...
like
...
cobalt,
...
iron
...
and
...
nickel.
...
Both
...
kinds
...
of
...
magnetism
...
involve
...
strong
...
correlations
...
and/or
...
strong
...
interactions
...
and
...
are
...
not
...
yet
...
completely
...
understood.
...
For
...
localized
...
spins,
...
major
...
open
...
questions
...
include
...
the
...
interplay
...
of
...
magnetism
...
with
...
d-wave
...
superfluidity
...
and
...
frustrated
...
spin
...
materials.
...
For
...
itinerant
...
ferromagnetism,
...
phase
...
transition
...
theories
...
are
...
still
...
qualitative.
...
What is needed for Itinerant Ferromagnetism?
