Atomic structure and magnetism of the Au-Ga-Ce 1/1 approximant crystal

TL;DR

This study investigates the atomic structure and magnetic properties of a newly discovered Au-Ga-Ce 1/1 approximant crystal, revealing a robust spin-glass state and Kondo behavior influenced by structural variations.

Contribution

It provides the first detailed analysis of how structural degrees of freedom affect magnetism and electronic behavior in Au-Ga-Ce approximant crystals.

Findings

Spin-glass state is the ground state across the entire phase region.

Gigantic low-temperature specific heat linked to spin-freezing, not heavy Fermion behavior.

Ce atoms at the cluster center exhibit Kondo impurity behavior.

Abstract

We report a new Au-Ga-Ce 1/1 approximant crystal (AC) which possesses a significantly wide single-phase region of 53 - 70 at% Au and 13.6 - 15.1 at% Ce. Single crystal X-ray structural analyses reveal the existence of two types of structural degrees of freedom, i.e., the Au/Ga mixing sites and the fractional Ce occupancy site: the former enables a large variation in the electron concentration and the latter allows a variation in the occupancy of a magnetic impurity atom at the center of the Tsai-type cluster. Following these findings, the influences of two types of structural modifications on the magnetism are thoroughly investigated by means of magnetic susceptibility and specific heat measurements on the Au-Ga-Ce 1/1 AC. The spin-glass (SG) state is found to be the ground state over the entire single-phase region, showing a robust nature of the SG state against both structural modifications. In addition, a gigantic specific heat (C/T) is commonly observed at low temperatures for all the compositions, which is consistently explained as a consequence of the spin-freezing phenomenon, not of a heavy Fermion behavior as reported elsewhere. Moreover, the origin of the SG state in the 1/1 Au-Ga-Ce AC is attributed to the existence of non-magnetic atom disorder in the Au/Ga mixing sites. Furthermore, a Kondo behavior is observed in the electrical resistivity at low temperatures, which is enhanced by increasing the Ce concentration, verifying that a Ce atom introduced at the cluster center behaves as a Kondo impurity for the first time.