Electron Spin Resonance of the Yb 4f moment in Yb(Rh1-xCox)2Si2

TL;DR

This study uses ESR spectroscopy to explore how spin dynamics and ground state properties evolve across the Yb(Rh1-xCox)2Si2 series, revealing continuous changes in crystal electric field and the influence of Kondo interactions and ferromagnetic correlations.

Contribution

It provides new insights into the evolution of spin dynamics and ground state wave functions across the series, highlighting the role of Co-doping in modifying magnetic interactions.

Findings

ESR spectra show well-defined Yb3+ character below 20 K across all compositions.

The ESR g-factor along c-axis increases with Co-content, indicating changes in crystal electric field.

Linewidth dependence on Co-content suggests a balance between Kondo interaction and ferromagnetic correlations.

Abstract

[published in Phys. Rev. B 85, 035119 (2012)] The evolution of spin dynamics from the quantum critical system YbRh2Si2 to the stable trivalent Yb system YbCo2Si2 was investigated by Electron Spin Resonance (ESR) spectroscopy. While the Kondo temperature changes by one order of magnitude, all compositions of the single crystalline series Yb(Rh1-xCox)2Si2 show well defined ESR spectra with a clear Yb3+ character for temperatures below \approx 20 K. With increasing Co-content the ESR g-factor along the c-direction strongly increases indicating a continuous change of the ground state wave function and, thus, a continuous change of the crystal electric field. The linewidth presents a complex dependence on the Co-content and is discussed in terms of the Co-doping dependence of the Kondo interaction, the magnetic anisotropy and the influence of ferromagnetic correlations between the 4f states. The results provide evidence that, for low Co-doping, the Kondo interaction allows narrow ESR spectra despite the presence of a large magnetic anisotropy, whereas at high Co-concentrations, the linewidth is controlled by ferromagnetic correlations. A pronounced broadening due to critical correlations at low temperatures is only observed at the highest Co-content. This might be related to the presence of incommensurate magnetic fluctuations.