Low‐temperature values of the magnetocrystalline anisotropy constantK1for several nickel ferrous ferrites were measured using the torque method. These were compared to existing microwaveK1values for the same crystals. The incremental &Dgr;K1=K1(torque)‐K1(microwave) were found to increase to well‐defined maxima below 77°K and then to decrease toward zero at 4.2°K. The temperature at which the maximum value of &Dgr;K1occurred increased with increasing Fe2+concentration. The low‐temperature maxima and subsequent sharp decreases in &Dgr;K1cannot be fit to earlier theory which was successful above 77°K. This indicates the loss mechanism responsible for &Dgr;K1at higher temperatures becomes inoperative at liquid‐helium temperatures. The maximum value of &Dgr;K1is found to depend on the Ni2+concentration as well as Fe2+concentration. This suggests that the Ni2+ions may also be involved in the relaxation mechanism responsible for &Dgr;K1.