四重态CeAg $_2$ Ge $_2$单晶的准四重晶体电场基态
Quasi-quartet crystal electric field ground state in a tetragonal CeAg$_2$Ge$_2$ single crystal
摘要：
本文首次采用助熔剂法成功地生长了CeAg $_2$ Ge $_2$单晶，并通过测量其电阻率、磁化率和比热容研究了其各向异性的物理性质。我们发现CeAg $_2$ Ge $_2$在$T_{\rm N}$ = 4.6 K时发生反铁磁转变。电阻率和磁化率数据显示出很强的各向异性磁性。对于饱和磁化强度为1.6 $μ_{\rm B}$ /Ce的$H \parallel$ [100]，在$T$ = 2 K时测量的磁化强度在$H_{\rm m1}$ = 31 kOe和$H_{\rm m2}$ = 44.7 kOe时显示出两个变磁跃迁。反磁化率数据的晶体电场（CEF）分析揭示了CeAg $_2$ Ge $_2$的基态和第一激发态是紧密间隔的，表明准四重态基态。比热数据进一步支持存在紧密间隔的能级。
英文摘要：
We have successfully grown the single crystals of CeAg$_2$Ge$_2$, for the first time, by flux method and studied the anisotropic physical properties by measuring the electrical resistivity, magnetic susceptibility and specific heat. We found that CeAg$_2$Ge$_2$ undergoes an antiferromagnetic transition at $T_{\rm N}$ = 4.6 K. The electrical resistivity and susceptibility data reveal strong anisotropic magnetic properties. The magnetization measured at $T$ = 2 K exhibited two metamagnetic transitions at $H_{\rm m1}$ = 31 kOe and $H_{\rm m2}$ = 44.7 kOe, for $H \parallel$ [100] with a saturation magnetization of 1.6 $μ_{\rm B}$/Ce. The crystalline electric field (CEF) analysis of the inverse susceptibility data reveals that the ground state and the first excited states of CeAg$_2$Ge$_2$ are closely spaced indicating a quasi-quartet ground state. The specific heat data lend further support to the presence of closely spaced energy levels.
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