[Paper Review] Magnetic order and transport in the heavy-fermion system CeCu_{6-x}Au_x

H. v. Löhneysen, Andreas Neubert+6 more|arXiv (Cornell University)|Feb 20, 1998

Rare-earth and actinide compounds4 citations

TL;DR

This study investigates magnetic order and transport in CeCu_{6-x}Au_x heavy-fermion systems using elastic neutron scattering and electrical resistivity measurements. It identifies incommensurate antiferromagnetic order with a wave vector near Q ≈ (0.625 0 0.275) for x = 0.2, evolving to Q ≈ (0.59 0 0) at x = 0.5, and shows that the magnetic moment increases with doping, while resistivity data reveal clear signatures of magnetic order, explained by Kondo effect suppression and anisotropic band structure near 2k_F.

ABSTRACT

We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu_{6-x}Au_x single crystals for x > 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector Q $\approx$ (0.625 0 0.275) for x=0.2, nearly unchanged for x=0.3, and Q $\approx$ (0.59 0 0) for x=0.5, staying roughly the same for x=1.0. In addition, short-range correlations are observed at x=0.2, reminiscent of those found previously for x=0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vector Q is close to 2 k_F, where k_F is a typical Fermi momentum.

Motivation & Objective

• To determine the magnetic ordering wave vector and magnetic moment in CeCu_{6-x}Au_x single crystals across varying gold doping (x).
• To investigate the interplay between magnetic order and electronic transport in heavy-fermion systems.
• To understand how the Kondo effect and electronic band structure influence resistivity and magnetic correlations.
• To test the theoretical prediction that magnetic order near 2k_F leads to enhanced transport anomalies.

Proposed method

• Elastic neutron scattering was used to probe the magnetic structure and determine the ordering wave vector Q in single crystals of CeCu_{6-x}Au_x for x = 0.2, 0.3, 0.5, and 1.0.
• Electrical resistivity was measured along all three crystallographic directions to detect signatures of magnetic order.
• The magnetic moment was extracted from neutron scattering intensity data and analyzed as a function of doping x.
• Theoretical modeling considered the suppression of the Kondo effect by staggered magnetization and the role of anisotropic band structure.
• Theoretical analysis assumed that the ordering wave vector Q is close to 2k_F, where k_F is the Fermi momentum, to explain observed transport anomalies.

Experimental results

Research questions

• RQ1 What is the wave vector of the magnetic order in CeCu_{6-x}Au_x across different gold doping levels?
• RQ2 How does the magnetic moment evolve with increasing gold doping (x)?
• RQ3 What is the relationship between the specific-heat anomaly at the ordering temperature and the magnetic moment?
• RQ4 How does the electrical resistivity respond to the onset of magnetic order, and what does it reveal about electronic correlations?
• RQ5 To what extent can the observed transport behavior be explained by Kondo effect suppression and anisotropic band structure near 2k_F?

Key findings

• The magnetic ordering wave vector is incommensurate, with Q ≈ (0.625 0 0.275) for x = 0.2, and remains nearly unchanged at x = 0.3, evolving to Q ≈ (0.59 0 0) for x = 0.5 and x = 1.0.
• The ordered magnetic moment increases rapidly for small x (x = 0.2), with a slower increase for larger x, consistent with the observed enhancement of the specific-heat anomaly at T_N.
• Short-range magnetic correlations are observed at x = 0.2, reminiscent of those previously reported at x = 0.1.
• Electrical resistivity measurements show clear anisotropic signatures of magnetic order, with distinct behavior along different crystallographic directions.
• Theoretical modeling attributes the transport anomalies to partial suppression of the Kondo effect by the staggered magnetization and to anisotropy in the electronic band structure induced by the staggered field.
• The agreement between experiment and theory is strongest when the ordering wave vector Q is close to 2k_F, supporting the theoretical framework.