ANTIFERROMAGNETISM OF CS2MNCL4.2H2O

Single-crystal magnetic susceptibilities of triclinic Cs2MnCl4•2H2O have been measured between 0.35 and 20A°K. Over this interval the susceptibility exhibits a uniaxial anisotropy about a direction parallel to the O-Mn-O axis of each octahedral complex [MnCl4•2H2O]2-. The temperature variations of χII and χa are those of a uniaxial antiferromagnet with TN=1.8A°K and the preferred direction of spin alignment along or near the O-Mn-O axis. Quantitative estimates of the magnetic dipolar anisotropy indicate it to be an order of magnitude too small to account for the observations above TN. This anisotropy can be described by a term DSz2 in the single-ion Hamiltonian with D=-0.1 cm-1. In the ordered state, this relatively large anisotropy produces a gap kTAE, in the spin-wave spectrum with an estimated TAEa 1.6A°K. A gap of roughly this magnitude is suggested by the temperature variation of χII below 1A°K. The nearest-neighbor exchange coupling is estimated to be zJ=-0.54k. © 1969 The American Physical Society.