Evolution of magnetism in Yb(Rh_(1-x)Co_x)2Si2

TL;DR

This study explores how magnetism evolves in the Yb(Rh_(1-x)Co_x)2Si2 series, revealing complex phase behavior, reduced Kondo temperature, and magnetic competition, shedding light on quantum criticality near YbRh2Si2.

Contribution

It provides detailed experimental insights into the magnetic phase diagram and electronic localization in Yb(Rh_(1-x)Co_x)2Si2, highlighting the effects of chemical pressure and quantum criticality.

Findings

Complex magnetic phase diagram with tricritical points.

Reduction of Kondo temperature with Co substitution.

Evidence of magnetic competition between ferromagnetic and antiferromagnetic interactions.

Abstract

We present a study of the evolution of magnetism from the quantum critical system YbRh2Si2 to the stable trivalent Yb system YbCo2Si2. Single crystals of Yb(Rh_(1-x)Co_x)2Si2 were grown for 0 < x < 1 and studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements, as well as photoemission spectroscopy. The results evidence a complex magnetic phase diagram, with a non-monotonic evolution of T_N and two successive transitions for some compositions resulting in two tricritical points. The strong similarity with the phase diagram of YbRh2Si2 under pressure indicates that Co substitution basically corresponds to the application of positive chemical pressure. Analysis of the data proves a strong reduction of the Kondo temperature T_K with increasing Co content, T_K becoming smaller than T_N for x ~ 0.5, implying a strong localization of the 4f electrons. Furthermore, low-temperature susceptibility data confirm a competition between ferromagnetic and antiferromagnetic exchange. The series Yb(Rh_(1-x)Co_x)2Si2 provides an excellent experimental opportunity to gain a deeper understanding of the magnetism at the quantum critical point in the vicinity of YbRh2Si2 where the antiferromagnetic phase disappears (T_N=>0).