顺磁Ce和Yb类质同象的不同变磁性
Different metamagnetism between paramagnetic Ce and Yb isomorphs
摘要：
为了解决重费米子系统中的变磁现象之谜，我们比较了顺磁同质结构Ce和Yb系统，CeNi $_2$ Ge $_2$和YbNi $_2$ Ge $_2$，它们都位于磁不稳定性附近。最有趣的结果是在脉冲磁场中的磁化测量发现了两个系统中的变磁性转变。这是Ce和Yb类质同象顺磁系统的变磁性的首次观测。类似于其他的变磁体，两种化合物的变磁性转变场都很好地由温度$T_χ^{\rm max}$来缩放，在该温度下磁化率显示出最大值。此外，CeNi $_2$ Ge $_2$的非线性磁化率$χ_3$的峰值出现在$T_χ^{\rm max}/2$附近，与其它重费米子超磁体一样。相反，YbNi $_2$ Ge $_2$在$T_χ^{\rm max}$处仅显示$χ_3$的符号变化，如在位于铁磁临界点附近的巡游变磁体中所观察到的。CeNi $_2$ Ge $_2$的变磁性对应于典型的近藤晶格系统，而YbNi $_2$ Ge $_2$的变磁性类似于近铁磁巡游系统。本文还讨论了YbNi $_2$ Ge $_2$变磁行为的其它可能性。
英文摘要：
To solve the puzzle of metamagnetic phenomena in heavy fermion systems, we have compared paramagnetic isostructural Ce and Yb systems, CeNi$_2$Ge$_2$ and YbNi$_2$Ge$_2$, both of which are located near a magnetic instability. The most intriguing result is discovery of a metamagnetic-like transition in both systems from magnetization measurements in a pulsed magnetic fields. This is the first observation of the metamagnetism for isomorphic Ce and Yb paramagnetic systems. Similar to other metamagnets, the metamagnetic transition fields for both compounds are well scaled by the temperature $T_χ^{\rm max}$, at which the magnetic susceptibility shows a maximum. In addition, for CeNi$_2$Ge$_2$ a peak of nonlinear susceptibility $χ_3$ appears at approximately $T_χ^{\rm max}/2$, as for other heavy-fermion metamagnets. In contrast, YbNi$_2$Ge$_2$ shows only a sign change for $χ_3$ at $T_χ^{\rm max}$, as observed in itinerant metamagnets located near the ferromagnetic critical point. The metamagnetism of CeNi$_2$Ge$_2$ corresponds to a typical Kondo lattice system, whereas that of YbNi$_2$Ge$_2$ is similar to the nearly ferromagnetic itinerant systems. Other possibilities for the metamagnetic behavior of YbNi$_2$Ge$_2$ are also discussed.
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