Magnetism and crystalline electric field effect in ThCr2Si2-type CeNi2As

Yongkang Luo

¹

,

Jin‐Ke Bao

²

,

Chengchao Shen

³

et al.

Abstract

A millimeter-sized ThCr 2 Si 2 -type CeNi 2 As 2 single crystal was synthesized by the 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 magnetic-field-induced spin-flop transition was seen below T N when the applied B is parallel to the c axis, the magnetic easy axis, together with a huge frustration parameter f = θ W /T N . A pronounced Schottky-type 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 1 = 325 K and 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.

Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi 2− δ As 2

“…A magnetic structure was proposed in ref. 8 but remains to be confirmed; nevertheless, the existence of a spin-flop transition below T N suggests that the order is of a local-moment type, which is also consistent with a modest zero-temperature Sommerfeld coefficient of 65 mJ/mol · K 2 estimated by extrapolating the specific heat divided by temperature from above T N (8). The magnetic entropy below T N of ∼0.6R ln 2 indicates magnetic order in a crystalline electric field (CEF) doublet ground state and some f-c hybridization.…”

“…Millimeter-sized single crystals of ThCr 2 Si 2 -type CeNi 2−δ As 2 were synthesized by a NaAs-flux method as described elsewhere (8). Rietveld analysis of X-ray spectra obtained on powdered single crystals confirms the I4/mmm structure and indicates that the Ni site occupancy is 0.856, close to the result of 0.86 obtained from energy-dispersive X-ray microanalysis measurements.…”

“…The reason for such a low carrier density in CeNi 2−δ As 2 is still unclear, but it is possible that Ni deficiency (8,9) has shifted the Fermi level, leaving only a few carriers in the bottom of the renormalized conduction band. At pressures close to and well above 2.7 GPa, the transverse Hall resistivity remains nonlinear in field, reflecting the sum of skew scattering due to strong paramagnetism of Ce moments and a contribution from the normal Hall effect.…”

“…Well below this possible orthorhombic distortion, Ce moments order antiferromagnetically at T N ≈ 5 K (Fig. S1A) (8,9), with the c axis being the magnetic easy axis. In the presence of an external magnetic field B k c, the ordered Ce moments undergo a weakly first-order spin-flop transition from an antiferromagnetic (AFM) ground state to a polarized paramagnetic state.…”

“…139) but may undergo a very weak orthorhombic distortion at low temperature (8). Well below this possible orthorhombic distortion, Ce moments order antiferromagnetically at T N ≈ 5 K (Fig.…”