Each arrow is a tiny magnetic domain in a 3D lattice. As the
external field H increases, domains rotate to align with it; when
H is removed some alignment remains — that lag traces the classic
B–H hysteresis loop, plotted live in the inset chart. The loop's
key landmarks are saturation (all domains aligned, the flat
top/bottom of the loop), remanence (the magnetization M that
remains when H returns to zero) and coercivity (the reverse
field needed to drive M back to zero).
- External field H — the driving field; sweeping it
traces the loop.
- Temperature — thermal energy that jostles each domain
out of alignment, shrinking both the loop and the peak
magnetization as it climbs toward the Curie point.
- Coercivity — how strongly domains resist flipping;
raising it widens the loop and needs a bigger reverse field to
erase remanence.
Real materials trade this off deliberately: hard-drive platters
and permanent magnets want high coercivity so stored magnetization
survives stray fields, while transformer and inductor cores want
low coercivity (a thin, "soft" loop) to minimize hysteresis losses
on every AC cycle.