We have investigated the finite temperature magnetic ordering in the quasi-two-dimensional Heisenberg antiferromagnetic system $({\mathrm{C}}_n{\mathrm{H}}_{2n+1}{\mathrm{NH}}_3{)}_2{\mathrm{MnCl}}_4$ with various chain lengths n. Our results indicate that in long-chain compounds with large interlayer distances, secondary interactions in magnitude besides the exchange interaction, such as the Ising anisotropy and the Dzyaloshinsky-Moriya interaction, play an important role in the magnetic phase transitions.

• Received 14 January 2000

DOI:https://doi.org/10.1103/PhysRevB.62.95