Magnetic order induced by Fe substitution of Al site in the heavy fermion systems alpha-YbAlB4 and beta-YbAlB4

TL;DR

This study demonstrates that Fe substitution in heavy fermion systems alpha- and beta-YbAlB4 induces magnetic order, revealing the role of chemical pressure in suppressing Kondo screening and promoting magnetism.

Contribution

It is the first to show Fe substitution induces magnetic order in both alpha- and beta-YbAlB4, highlighting the impact of chemical pressure on heavy fermion behavior.

Findings

Fe substitution induces magnetic order at 7-9 K in both compounds.

Fe substitution causes volume contraction without changing crystal structure.

Magnetic order likely of a canted antiferromagnetic type.

Abstract

beta-YbAlB4 is a heavy fermion superconductor that exhibits a quantum criticality without tuning at zero field and under ambient pressure. We have succeeded in substituting Fe for Al in beta-YbAlB4 as well as the polymorphous compound alpha-YbAlB4, which in contrast has a heavy Fermi liquid ground state. Full structure determination by single crystal X-ray diffraction confirmed no change in crystal structure for both alpha- and beta-YbAlB4, in addition to volume contraction with Fe substitution. Our measurements of the magnetization and specific heat indicate that both alpha-YbAl0.93Fe0.07B4 and beta-YbAl0.94Fe0.06B4 exhibit a magnetic order, most likely of a canted antiferromagnetic type, at $7\sim 9$ K. The increase in the entropy as well as the decrease in the antiferromagnetic Weiss temperature with the Fe substitution in both systems indicates that the chemical pressure due to the Fe substitution suppresses the Kondo temperature and induces the magnetism.