Ground-state properties of the double trillium lattice antiferromagnet KBaCr$_2$(PO$_4$)$_3$

TL;DR

This study investigates the magnetic properties of the double trillium lattice material KBaCr$_2$(PO$_4$)$_3$, revealing two magnetic transitions and clarifying the nature of magnetic ordering and frustration in this complex structure.

Contribution

The paper provides the first detailed experimental and theoretical analysis of the magnetic ground state of KBaCr$_2$(PO$_4$)$_3$, demonstrating the elimination of frustration due to its unique ferromagnetic and antiferromagnetic sublattice coupling.

Findings

Magnetic transition at T_N1 ≈ 13.5 K and T_N2 ≈ 7 K observed.

NMR data confirms 3D magnetic ordering at T_N1.

Ordered state follows T^3 relaxation behavior indicating two-magnon Raman process.

Abstract

Trillium lattices formed by corner-shared triangular units are the platform for magnetic frustration in three dimensions. Herein, we report structural and magnetic properties of the Cr-based double trillium lattice material KBaCr$_2$(PO$_4$)$_3$ studied by x-ray diffraction, magnetization, heat capacity, thermal conductivity, and $^{31}$P nuclear magnetic resonance (NMR) measurements complemented by density-functional band-structure calculations. Heat capacity and $^{31}$P NMR measurements reveal the magnetic transition at $T_{\rm N1} \simeq 13.5$ K in zero field followed by another transition at $T_{\rm N2} \simeq 7$ K in weak applied fields. The NMR sublattice magnetization confirms that the transition at $T_{\rm N1}$ is 3D in nature. The $^{31}$P spin-lattice relaxation rate in the ordered state follows the $T^3$ behavior indicative of the two-magnon Raman process. The spin lattice of KBaCr$_2$(PO$_4$)$_3$ comprises two crystallographically nonequivalent ferromagnetic sublattices that are coupled antiferromagnetically, thus eliminating frustration in this trillium network.