# Dynamics and field-induced order in the layered spin $S=1/2$ dimer system (C$_5$H$_6$N$_2$F)$_2$CuCl$_4$

## TL;DR

This study investigates the magnetic excitations and field-induced ordering in a layered S=1/2 dimer system using neutron scattering, calorimetry, and NMR, revealing a spin gap and a transition to antiferromagnetic order under magnetic field.

## Contribution

It provides detailed experimental characterization of the spin dynamics and field-induced phase transition in a quasi-two-dimensional dimer system, highlighting the interplay between magnetic field and quantum spin states.

## Key findings

- Dispersive triplet excitations with a spin gap of 1.112 meV
- Field-induced antiferromagnetic order at 8.5 T
- Layered structure with distinct intra- and interlayer bandwidths

## Abstract

The quasi-two-dimensional Heisenberg spin $S=1/2$ dimer system bis(2-amino-5-fluoro-pyridinium) tetrachlorocuprate(II) is studied by means of inelastic neutron scattering, calorimetry and nuclear magnetic resonance (NMR) experiments. In the absence of an applied magnetic field we find dispersive triplet excitations with a spin gap of $\Delta=1.112(15)$ meV and a bandwidth of $0.715(15)$ meV within the layers and $0.116(15)$ meV between the layers, respectively. In an applied magnetic field of $\mu_0H_c\approx 8.5$ T the spin gap is closed and we find a field induced antiferromagnetically ordered phase.