“…The spin Hamiltonian of NiSnCl 6 ·6H 2 O for the field parallel to the [111] direction (zaxis) is described as H = g z µ B S z H z + DS 2 z , where g z , µ B , S z , H z and D are the g-value, the Bohr magneton, the spin quantum number (S z = −1, 0, 1), the external magnetic field and the D-value, respectively. As the D-value is known to be positive [23], this compound is certainly a candidate for a substance exhibiting a longitudinal mode under pressure [25]. From this Hamiltonian, two linear resonance conditions, which intercept the frequency axis with the opposite signs, hν = g z µ B H z ± D, are obtained, where h and ν are the Planck constant and the frequency, respectively.…”