Magnetic properties of the Haldane-gap material NENB

TL;DR

This study investigates the magnetic properties of the Haldane-gap material NENB using magnetization and ESR techniques, confirming the Haldane state and analyzing its magnetic excitations and anisotropies.

Contribution

It provides detailed experimental characterization of NENB's magnetic excitations, spin-Hamiltonian parameters, and evidence of chain-end states, advancing understanding of Haldane-chain materials.

Findings

Confirmed the Haldane state in NENB.

Determined spin-Hamiltonian parameters: Delta=17.4 K, g_parallel=2.14, D=7.5 K, |E|=0.7 K.

Observed fractional S=1/2 chain-end states causing spin-glass effects.

Abstract

Results of magnetization and high-field ESR studies of the new spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding Delta = 17.4 K, g_parallel = 2.14, D = 7.5 K, and |E| = 0.7 K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which origin is discussed.