Diamagnetic materials M = χH
CS: 30.10
B = (1 + χ ) µ 0 H
Susceptibility is small (weak) and negative: χ < 0 → µ < µ0. Linear response (χ independent of H): no permanent M when H = 0. Susceptibility (χ) smaller at high-T due to thermal disorder. All materials are weakly diamagnetic if they lack atomic moments. When moments are present, diamagnetism isn’t noticeable. Weakly repelled from a magnetic field.
http://www.physics.ucla.edu/marty/diamag/