Field Dependent Phase Diagram of the Quantum Spin Chain (CH3)2NH2CuCl3

Although (CH3)2NH2CuCl3 (MCCL) was first examined in the 1930’s, there are open questions regarding the magnetic dimensionality and nature of the magnetic properties. MCCL is proposed to be a S=1/2 alternating ferromagnetic‐antiferromagnetic spin chain alternating along the crystalline a‐axis. Proposed ferromagnetic (JFM =1.3 meV) and antiferromagnetic (JAFM = 1.1 meV) exchange constants make this system particularly interesting for experimental study. Because JFM and JAFM are nearly identical, the system should show competing behavior between S=1/2 (AFM) and S=1(FM) effects. We report low temperature magnetic field dependent susceptibility, χ, and specific heat, Cp, of MCCL. These provide an initial magnetic‐field versus temperature phase diagram. A zero‐field phase transition consistent with long range magnetic order is observed at T=0.9 K. The transition temperature can be reduced via application of a magnetic field. We also present comparisons to a FM/AFM dimer model that accounts for χ(T,H=0) and Cp(...