Experimental and Theoretical Study of the Phase Diagram of the Linear Antiferromagnet (CH₃)₄NMnCl₃ (TMMC)

Magnetic phase diagrams of the most typical quasi-one-dimensional antiferromagnet (CH₃)₄ NMnCl₃ (T_N=0.835 K) reported in our previous paper have been investigated in more detail by heat capacity and magnetic susceptibility measurements in external magnetic fields up to 30 kOe. The phase diagrams for the external field applied along the in-plane easy and hard axes normal to the magnetic chain are reproduced satisfactorily by the theory in which the classical anisotropic XY model is assumed for the magnetic chain and interchain interarctions are treated within the molecular field approximation. The magnitude of the anisotropy field in the plane normal to the chain is determined to be 93 Oe.