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arXiv 1206.4472cond-mat.str-el
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弱铁磁氧化物LaCo $_{0.8}$ Rh $_{0.2}$ O $_{3}$中Ga的$^{3+}$替代效应

Ga$^{3+}$-substitution effects in the weak ferromagnetic oxide LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$

Shinichiro Asai, Noriyasu Furuta, Ryuji Okazaki, Yukio Yasui, Ichiro Terasaki

备注：
5 pages, 6 figures
发表信息：
Phys. Rev. B 86, 014421, (2012)
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摘要：

为了通过Ga $^{3+}$的替代效应来了解Co $^{3+}$的自旋状态，对$0 \leq y \leq 0.15$的LaCo $_{0.8-y}$ Rh $_{0.2}$ Ga $_{y}$ O $_{3}$多晶样品进行了磁化强度和X射线衍射测量. LaCo $_{0.8}$ Rh $_{0.2}$ O $_{3}$中的铁磁有序在15 K以下被Ga $^{3+}$取代显著抑制，其中铁磁体积分数线性降低。正常状态下的磁化率也系统地减少与Ga含量，从我们发现，一个Ga $^{3+}$离子减少4.6 $μ_{\rm B}$每分子式单位。我们已经评估了如何使用扩展的居里-外斯定律的高自旋态钴$^{3+}$的浓度随温度的变化，并已发现，取代Rh $^{3+}$离子稳定的高自旋态钴$^{3+}$离子下降到低温。我们发现Ga $^{3+}$优先取代高自旋态Co $^{3+}$，这与我们以前的发现Rh $^{3+}$优先取代低自旋态Co $^{3+}$形成了显著的对比。这些结果表明LaCoOPDMATHABMP在室温下的磁激发态是高自旋态CoPDMATHABMR和低自旋态CoPDMATHABMR的混合态。

英文摘要：

Magnetization and x-ray diffraction have been measured on polycrystalline samples of LaCo$_{0.8-y}$Rh$_{0.2}$Ga$_{y}$O$_{3}$ for $0 \leq y \leq 0.15$ in order to understand the spin state of Co$^{3+}$ through the Ga$^{3+}$ substitution effect. The ferromagnetic order in LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$ below 15 K is dramatically suppressed by the Ga$^{3+}$ substitution, where the ferromagnetic volume fraction is linearly decreased. The normal state susceptibility also systematically decreases with the Ga content, from which we find that one Ga$^{3+}$ ion reduces 4.6 $μ_{\rm B}$ per formula unit. We have evaluated how the concentration of the high-spin state Co$^{3+}$ changes with temperature by using an extended Curie-Weiss law, and have found that the substituted Rh$^{3+}$ ion stabilizes the high-spin state Co$^{3+}$ ion down to low temperatures. We find that Ga$^{3+}$ preferentially replaces the high-spin state Co$^{3+}$, which makes a remarkable contrast to our previous finding that Rh$^{3+}$ preferentially replaces the low-spin state Co$^{3+}$. These results strongly suggest that the magnetically excited state of LaCoO$_{3}$ at room temperature is a mixed state of high-spin state Co$^{3+}$ and low-spin state Co$^{3+}$.

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