Cu-doping effects on the ferromagnetic semimetal CeAuGe

TL;DR

This study investigates how copper doping affects the crystal structure, magnetic properties, and electronic behavior of the ferromagnetic semimetal CeAuGe, revealing structural transitions and magnetic ordering changes across the doping range.

Contribution

It provides a comprehensive analysis of Cu substitution effects on the structure and magnetic order in CeAuGe, including neutron diffraction and symmetry analysis, which was previously unexplored.

Findings

Cu doping induces a structural transition from non-centrosymmetric to centrosymmetric phases.

All doped compounds exhibit magnetic transitions near 10 K, with a maximum of 12 K at x=0.5.

Resistivity shows Kondo effects at high doping levels and anomalies near magnetic transitions.

Abstract

We present a study of Cu-substitution effects in 4f-Ce intermetallic compound CeAu1-xCuxGe, with potentially unusual electronic states, in the whole concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric (P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice constant has a maximum value. Magnetic susceptibility and electrical resistivity measurements reveal that all Cu-doped compounds undergo magnetic phase transition near 10 K, with the maximum transition temperature of 12 K for x = 0.5. The neutron powder diffraction experiments show the ferromagnetic ordering of Ce3+ magnetic moments with a value of ~ 1.2 Bohr magneton at 1.8 K, oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we have found the solutions for the magnetic structure in the ferromagnetic Shubnikov space groups Cmc'21' and P21'/m' for x < 0.5 and x >= 0.5, respectively. Electrical resistivity exhibits a metallic temperature behaviour in all compounds. The resistivity has a local minimum in the paramagnetic state due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping level, x = 0.2, the resistivity shows a broad feature at the ferromagnetic transition temperature and an additional transition-like peculiarity at 2.5 K in the ferromagnetic state.