The FORCIT software package produces first-order reversal curve (FORC) diagrams and related plots (see examples below). It is available for use free of charge.

FORCIT (along with TRACKIT), their subroutines, and a Makefile are available in gzip/tar format or Stuffit format in files:

NOTE: This version of FORCIT was last updated in 2007. It is an archive version. Any new versions, if and when they are created, will be posted on Gary Acton's new web page.

For bug reports and suggestions for improvement, E-mail Gary Acton at


The plots created by FORCIT and TRACKIT are illustrated for
an ocean crust basalt sample (1256D-49R-2, 99 cm) from
Hole 1256D cored on Ocean Drilling Program Leg 206.

a) The instrument drift curve.

b) The FORC paths plotted in Ba vs. Br space.

c) The moment plotted in Ba vs. Br space.

d) The FORC paths plotted in B vs. M space.

e) A 2-d FORC diagram with the FORC distribution
plotted inside the hysteresis loop (B vs. M space).

f) A 2-d FORC diagram plotted in Ba vs. Br space.

  • B = Magnetic field (mT)
  • M = Magnetic Moment
  • Ba = Applied field
  • Br = Reversal field
  • Bc = Coercivity
  • Bb = Bias or Interaction

g) The micro-susceptibility, which is the first partial derivative,
plotted in Bc vs. Bb space.

h) The standard 2-d FORC diagram plotted in Bc vs. Bb space.

i) The FORC distribution along a profile where Bc = 0,
referred to as the quasi-reversible ridge.
Note that the peak magnitude is about eight times larger
than the maximum value in the standard 2-d FORC diagram.
This high magnitude quasi-reversible ridge is thus removed
from the 2-d and 3-d FORC diagrams in order to
accentuate the irreversible magnetization.

j) A 3-d FORC diagram (view angle 135°) plotted in vs. space.

k) A 3-d FORC diagram (view angle 45°) plotted in vs. space.

l) A 1-d plot of the FORC distribution produced by program TRACKIT.
The profile goes from (Bc, Bb) = (0, 0) to (Bc, Bb) = (100, 0).

Generally each plot also gives the sample name, data file name,
and other information, but these have been removed from this figure for space reasons.