Electron-spin-resonance in the doped spin-Peierls compound Cu(1-x)Ni(x)GeO3

TL;DR

This study uses ESR to investigate Ni-doped CuGeO3, revealing magnetic clustering, antiferromagnetic resonance behavior, and differences in magnetic gap formation depending on doping levels.

Contribution

It provides new insights into the magnetic properties and resonance spectra of Ni-doped CuGeO3, especially regarding the formation of magnetic clusters and the nature of the antiferromagnetic state.

Findings

Magnetic clusters form around Ni ions within the spin-Peierls matrix.

A magnetic resonance gap appears below the Neel temperature for x=0.032.

The spectrum remains gapless for x=0.017, indicating weak antiferromagnetic order.

Abstract

ESR-study of the Ni-doped spin-Peierls compound CuGeO3 has been performed in the frequency range 9-75 GHz. At low temperatures the g-factor is smaller than the value expected for Cu- and Ni-ions. This anomaly is explained by the formation of magnetic clusters around the Ni-ions within a nonmagnetic spin-Peierls matrix. The transition into the AFM-state detected earlier by neutron scattering for doped samples was studied by means of ESR. For x=0.032 a gap in the magnetic resonance spectrum is found below the Neel temperature and the spectrum is well described by the theory of antiferromagnetic resonance based on the molecular field approximation. For x=0.017 the spectrum below the Neel point remained gapless. The gapless spectrum of the antiferromagnetic state in weekly doped samples is attributed to the small value of the Neel order parameter and to the magnetically disordered spin-Peierls background.