Characterization of a Quasi-One Dimensional Spin-1/2 Magnet which is Gapless and Paramagnetic for g mu_B H <= J and k_B T << J

TL;DR

This study characterizes a one-dimensional spin-1/2 Heisenberg antiferromagnet, copper pyrazine dinitrate, demonstrating its gapless and paramagnetic behavior under various magnetic fields and temperatures, and providing experimental validation of theoretical models.

Contribution

It provides detailed experimental characterization of copper pyrazine dinitrate as an ideal 1D spin-1/2 Heisenberg antiferromagnet and compares results with Bethe ansatz calculations.

Findings

Material remains gapless and paramagnetic up to high fields and low temperatures.

Spinon velocity decreases by 32% with increasing magnetic field.

Experimental results agree with Bethe ansatz numerical calculations.

Abstract

High field mangetization, field-dependent specific heat measurements, and zero field inelastic magnetic neutron scattering have been used to explore the magnetic properties of copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2). The material is an ideal one-dimensional spin-1/2 Heisenberg antiferromagnet with nearest neighbor exchange constant J=0.90(1) meV and chains extending along the orthorhombic a-direction. As opposed to previosly studied molecular-based spin-1/2 magnetic systems, coppyer pyrazine dinitrate remains gapless and paramagnetic for g mu_B H/J at least up to 1.4 and for k_B T/J at least down to 0.03 this makes the material an excellent model system for exploring the T=0 critical line which is expected in the H - T phase diagram on the one-dimensional spin-1/2 Heisenberg antiferromagnet. As a first example of such a study we present accurate measurements of the Sommerfeld constant of the spinon gas versus g mu_B H/J < 1.4 which reveal a decrease of the averages spinon velocity by 32% in that field range. The results are in excellent agreement with numerical calculations based on the Bethe ansatz with no adjustable parameters.