Magnetic phase diagram of a 2-dimensional triangular lattice antiferromagnet Na$_2$BaMn(PO$_4$)$_2$

TL;DR

This study explores the magnetic phase transitions of a 2D triangular lattice antiferromagnet Na$_2$BaMn(PO$_4$)$_2$, revealing multiple magnetic phases and deviations from ideal models, contributing to understanding frustrated magnetism.

Contribution

First detailed experimental investigation of magnetic phases in Na$_2$BaMn(PO$_4$)$_2$, highlighting its classical 2D TL Heisenberg AFM behavior with easy-axis anisotropy and complex phase diagram.

Findings

Observed two magnetic transitions at 1.15 K and 1.30 K.

Identified a field-induced up-up-down phase between 1.9 T and 2.9 T.

Detected deviations from ideal models with hysteresis and weak phase transitions.

Abstract

We report the magnetic phase transitions of a spin-5/2, 2-dimensional triangular lattice antiferromagnet (AFM) Na$_2$BaMn(PO$_4$)$_2$. From specific heat measurements, we observe two magnetic transitions at temperatures 1.15 K and 1.30 K at zero magnetic field. Detailed AC magnetic susceptibility measurements reveal multiple phases including the $\uparrow$$\uparrow$$\downarrow$ (up-up-down)-phase between 1.9 T and 2.9 T at 47 mK when magnetic field is applied along the $c$ axis, implying that Na$_2$BaMn(PO$_4$)$_2$ is a classical 2$d$ TL Heisenberg AFM with easy-axis anisotropy. However, it deviates from an ideal model as evidenced by a hump region with hysteresis between the $\uparrow$$\uparrow$$\downarrow$ and $V$-phases and weak phase transitions. Our work provides another experimental example to study frustrated magnetism in 2$d$ TL AFM which also serves as a reference to understand the possible quantum spin liquid behavior and anomalous phase diagrams observed in sibling systems Na$_2$Ba$M$(PO$_4$)$_2$ ($M$ = Co, Ni).