Field-induced long-range magnetic order in the spin-singlet ground state system YbAl3C3: Neutron diffraction study

TL;DR

This study reveals that applying a magnetic field induces long-range magnetic order in YbAl3C3, a system with a non-magnetic spin-singlet ground state, highlighting complex frustration effects and phase transitions.

Contribution

It provides the first neutron diffraction evidence of field-induced magnetic order in YbAl3C3 and discusses the role of geometrical frustration in stabilizing the non-magnetic ground state.

Findings

Long-range magnetic order appears above 6T at low temperatures.

The ordered phase persists at temperatures higher than the spin gap.

An intermediate disordered phase likely exists between the singlet ground state and magnetic order.

Abstract

The $4f$-electron system YbAl$_3$C$_3$ with a non-magnetic spin-dimer ground state has been studied by neutron diffraction in an applied magnetic field. A long-range magnetic order involving both ferromagnetic and antiferromagnetic components has been revealed above the critical field H$_C\sim $ 6T at temperature T=0.05K. The magnetic structure indicates that the geometrical frustration of the prototype hexagonal lattice is not fully relieved in the low-temperature orthorhombic phase. The suppression of magnetic ordering by the remanent frustration is the key factor stabilizing the non-magnetic singlet ground state in zero field. Temperature dependent measurements in the applied field H=12T revealed that the long-range ordering persists up to temperatures significantly higher than the spin gap indicating that this phase is not directly related to the singlet-triplet excitation. Combining our neutron diffraction results with the previously published phase diagram, we support the existence of an intermediate disordered phase as the first excitation from the non-magnetic singlet ground state. Based on our results, we propose YbAl$_3$C$_3$ as a new material for studying the quantum phase transitions of heavy-fermion metals under the influence of geometrical frustration.