Specific Heat Study on a Novel Spin-Gapped System : (CH_3)_2NH_2CuCl_3

TL;DR

This study investigates the specific heat of a novel quasi-one-dimensional spin-gapped system, revealing unique magnetic phase behaviors and excitations, and compares findings with a new quantum spin chain model.

Contribution

It provides the first detailed specific heat analysis of (CH_3)_2NH_2CuCl_3, highlighting its unusual phase diagram and coexistence of magnetic excitations, supporting a new quantum spin chain model.

Findings

Observation of spontaneous antiferromagnetic ordering.

Detection of a double-structure in specific heat within the plateau field range.

Unusual magnetic phase diagram distinct from other quantum spin systems.

Abstract

Specific heat measurements down to 120mK have been performed on a quasi-one-dimensional $S=1/2$ spin-gapped system (CH$_3$)$_2$NH$_2$CuCl$_3$ in a magnetic field up to 8 T. This compound has a characteristic magnetization curve which shows a gapless ground state and a plateau at 1/2 of the saturation value. We have observed a spontaneous antiferromagnetic ordering and a field-induced one below and above the 1/2 plateau field range, respectively. The field versus temperature phase diagram is quite unusual and completely different from those of the other quantum spin systems investigated so far. In the plateau field range, a double-structure in the specific heat is observed, reflecting the coexistence of ferromagnetic and antiferromagnetic excitations. These behaviors are discussed on the basis of a recently proposed novel quantum spin chain model consisting of weakly coupled ferromagnetic and antiferromagnetic dimers.