Microscopic Origin of Reduced Magnetic Order in a Frustrated Metal

TL;DR

This study investigates the microscopic origins of reduced magnetic order in a frustrated metallic system, revealing the importance of quantum fluctuations and the limitations of spin-wave theory in describing low-energy spin dynamics.

Contribution

It demonstrates that charge degrees of freedom can be neglected in certain frustrated metals and identifies the critical exchange interactions influencing magnetic order.

Findings

Hamiltonians neglecting charge are suitable for low-density frustrated metals.

Antiferromagnetic exchange interactions are close to the critical ratio J2/J1=1/2.

Spin-wave theory fails to predict low-energy spin dynamics, which are dominated by overdamped excitations.

Abstract

Although magnetic frustration in metals provides a promising avenue for novel quantum phenomena, their microscopic interpretation is often challenging. Here we use the face-centered cubic intermetallic HoInCu$_4$ as model material to show that Hamiltonians neglecting the charge degree of freedom are appropriate for frustrated metals possessing low density of states at the Fermi surface. Through neutron scattering techniques we determine matching magnetic exchange interactions in the paramagnetic and field-polarized states using an effective spin-1 Heisenberg Hamiltonian, for which we identify antiferromagnetic nearest and next-nearest neighbour interactions $J_1$ and $J_2$ that are close to the critical ratio $J_2$/$J_1$ = 1/2. The study further provides evidence that spin-wave theory fails to predict the low-energy spin dynamics in the antiferromagnetic zero-field state, which is dominated by overdamped magnetic excitations. We conclude that the low-energy fluctuations arise from quantum fluctuations, accounting for the missing moment of the strongly renormalized magnetic long-range order.