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

TL;DR

This study investigates the magnetic phase diagram of the quantum spin chain (CH3)2NH2CuCl3, revealing a zero-field magnetic order and field-dependent phase transitions through susceptibility and specific heat measurements.

Contribution

It provides the first detailed magnetic field versus temperature phase diagram for MCCL, combining experimental data with a dimer model to understand its magnetic behavior.

Findings

Zero-field magnetic order at 0.9 K

Magnetic transition temperature decreases with applied field

Agreement with a ferromagnetic/antiferromagnetic dimer model

Abstract

Although (CH3)2NH2CuCl3 (MCCL) was first examined in the 1930's [1], 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 [2,3]. 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, chi(H), 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 chi(T,H=0) and Cp(H,T).