Magnetic property and crystalline electric field effect in ThCr$_2$Si$_2$-type CeNi$_2$As$_2$

TL;DR

This study synthesizes and investigates the magnetic and electronic properties of ThCr$_2$Si$_2$-type CeNi$_2$As$_2$, revealing its anisotropic antiferromagnetic behavior, crystalline electric field effects, and potential structural distortion due to magnetic frustration.

Contribution

It reports the synthesis and detailed physical characterization of ThCr$_2$Si$_2$-type CeNi$_2$As$_2$, highlighting its unique magnetic anisotropy and crystal field effects, which differ from previously studied variants.

Findings

CeNi$_2$As$_2$ is a highly anisotropic uniaxial antiferromagnet with $T_N$=4.8 K.

A field-induced spin flop transition occurs below $T_N$ when magnetic field is along the c-axis.

Crystalline electric field excitations are identified at 325 K and 520 K.

Abstract

Millimeter sized ThCr$_2$Si$_2$-type CeNi$_2$As$_2$ single crystal was synthesized by NaAs flux method and its physical properties were investigated by magnetization, transport and specific heat measurements. In contrast to the previously reported CaBe$_2$Ge$_2$-type CeNi$_2$As$_2$, the ThCr$_2$Si$_2$-type CeNi$_2$As$_2$ is a highly anisotropic uniaxial antiferromagnet with the transition temperature $T_N$=4.8 K. A field induced spin flop transition was seen below $T_N$ when the applied $\textbf{B}$ is parallel to the $\textbf{c}$-axis, the magnetic easy axis, together with a huge frustration parameter $f=\theta_W/T_N$. A pronounced Schottky-like anomaly in specific heat was also found around 160 K, which could be attributed to the crystalline electric field effect with the excitation energies being fitted to $\Delta_1=$325 K and $\Delta_2=$520 K, respectively. Moreover, the in-plane resistivity anisotropy and low temperature X-ray diffractions suggest that this compound is a rare example exhibiting a possible structure distortion induced by the $4f$-electron magnetic frustration.