Magnetic Field versus Temperature Phase Diagram of the Spin-1/2 Alternating Chain Compound F5PNN

TL;DR

This study investigates the magnetic field versus temperature phase diagram of an S=1/2 alternating chain compound, revealing symmetric phase boundaries in single crystals and potential incommensurate ordering in powders due to frustration.

Contribution

It provides detailed experimental phase diagrams and theoretical analysis highlighting the effects of frustration and inhomogeneity in different sample forms.

Findings

Sharp peak indicating field-induced magnetic ordering observed

Symmetric phase boundary in single crystal, distorted in powder

Possible incommensurate ordering due to frustration in powder

Abstract

We have measured the specific heat of the S = 1/2 alternating Heisenberg antiferromagnetic chain compound pentafluorophenyl nitronyl nitroxide in magnetic fields using a single crystal and powder. A sharp peak due to field-induced magnetic ordering (FIMO) is observed in both samples. The H-T phase boundary of the FIMO of the single crystal is symmetric with respect to the central field of the gapless field region HC1 < H < HC2, whereas it is distorted for the powder whose ordering temperatures are lower. An analysis employing calculations based on the finite temperature density matrix renormalization group indicates the possibility of novel incommensurate ordering due to frustration in the powder around the central field.