Based on a microbalance, we have constructed a low-field Faraday magne
tometer, which does not suffer from instability even with strongly fer
romagnetic samples. The intrinsic value of this technique is that simu
ltaneous gravimetric determination of the interstitial content (for ex
ample H, N or C) is possible. The design procedure is described and so
me sample measurements made while nitriding a sample of Nd2Fe14B are r
eported.