S=1/2 Kagome antiferromagnets Cs$_2$Cu$_3MF$_{12}$ with M=Zr and Hf

TL;DR

This study investigates the magnetic properties of Kagome lattice antiferromagnets Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$, revealing their exchange interactions, structural transitions, and weak ferromagnetism due to Dzyaloshinsky-Moriya interactions.

Contribution

The paper provides the first detailed measurements of magnetization and specific heat on these Kagome antiferromagnets, highlighting their magnetic ordering and weak ferromagnetism.

Findings

Antiferromagnetic exchange interactions of 360 K and 540 K.

Structural phase transitions at 210 K and 175 K.

Magnetic ordering at around 24 K with weak ferromagnetism.

Abstract

Magnetization and specific heat measurements have been carried out on Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$ single crystals, in which Cu$^{2+}$ ions with spin-1/2 form a regular Kagom\'{e} lattice. The antiferromagnetic exchange interaction between neighboring Cu$^{2+}$ spins is $J/k_{\rm B}\simeq 360$ K and 540 K for Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$, respectively. Structural phase transitions were observed at $T_{\rm t}\simeq 210$ K and 175 K for Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$, respectively. The specific heat shows a small bend anomaly indicative of magnetic ordering at $T_\mathrm{N}= 23.5$ K and 24.5 K in Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$, respectively. Weak ferromagnetic behavior was observed below $T_\mathrm{N}$. This weak ferromagnetism should be ascribed to the antisymmetric interaction of the Dzyaloshinsky-Moriya type that are generally allowed in the Kagom\'{e} lattice.