Measurement of the spin-wave specific heat of antiferromagnetic CoCl26H2O and NiCl26H2O

Measurement of the spin-wave specific heat of two antiferromagnetic salts CoCl 2 6H 2 O and NiCl 2 6H 2 O is reported in the temperature range 0.7 °K to 4.0 °K. The temperature dependence of the specific heat of both salts is that which would be predicted by spin-wave theory were the energy gap in the spin-wave dispersion relation less than or equal to approximately half the value obtained by antiferromagnetic resonance. The presence of states within the spin-wave energy gap is discussed.