Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T

TL;DR

This study reveals weak antiferromagnetic order with significant quantum fluctuations in a quasi-2D S=3/2 kagome antiferromagnet, showing less than 50% sublattice polarization at low temperatures.

Contribution

It provides the first detailed experimental characterization of magnetic order and quantum fluctuations in a S=3/2 kagome antiferromagnet with partial site occupancy.

Findings

Weak long-range antiferromagnetic order observed.

Ordered moment is about one third of the classical value.

Gapless quantum spin fluctuations dominate the spin dynamics.

Abstract

We have found weak long range antiferromagnetic order in the quasi-two-dimensional insulating oxide $ KCr_3(OD)_6(SO_4)_2$ which contains Cr$^{3+}$ S=3/2 ions on a kagom\'{e} lattice. In a sample with $\approx$ 76% occupancy of the chromium sites the ordered moment is 1.1(3)$\mu_B$ per chromium ion which is only one third of the N\'{e}el value $g\mu_BS=3\mu_B$. The magnetic unit cell equals the chemical unit cell, a situation which is favored by inter-plane interactions. Gapless quantum spin-fluctuations ($\Delta/k_B <0.25$K) with a bandwidth of 60K >> $T_N$ = 1.6K are the dominant contribution to the spin correlation function, $S(Q,\omega)$ in the ordered phase.