A new collective phenomenon arising from spin anisotropic perturbations to a Heisenberg square lattice manifested in paramagnetic resonance experiments

TL;DR

This paper reports a novel collective phenomenon in Cu spin-1/2 systems where a gap appears in the magneto-optical spectrum at low temperatures, explained by spin anisotropy effects.

Contribution

It introduces a new collective behavior caused by spin anisotropic perturbations in a Heisenberg square lattice, observed through paramagnetic resonance experiments.

Findings

Observation of an unexpected gap in the absorption spectrum at low temperatures.

Simulation results that match experimental shifts, revealing the magnitude of spin anisotropy.

Identification of a collective phenomenon arising from spin anisotropy in Cu spin-1/2 systems.

Abstract

We report unexpected behaviour in a family of Cu spin- 1/2 systems, in which an apparent gap in the low energy magneto-optical absorption spectrum opens at low temperature. This previously unreported collective phenomenon arises at temperatures where the energy of the dominant exchange interaction exceeds the thermal energy. Simulations of the observed shifts in electron paramagnetic resonance spectral weight, which include spin anisotropy, reproduce this behavior yielding the magnitude of the spin anisotropy in these compounds.