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arXiv 0808.2247cond-mat.supr-con
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Eu $_{1-x}$ La $_x$ Fe $_2$ As $_2$单晶中的磁性phase diagram

Magnetic phase diagram in Eu$_{1-x}$La$_x$Fe$_2$As$_2$ single crystals

T. Wu, G. Wu, H. Chen, Y. L. Xie, R. H. Liu, X. F. Wang, X. H. Chen

摘要:

本文系统地测量了Eu $_{1-x}$ La $_x$ Fe $_2$ As $_2$单晶在不同磁场(H)下的电阻率、磁化率和比热。发现在临界磁场下,$Eu^{2+}$的磁性子晶格发生了从A型反铁磁性到铁磁性的变磁转变。随着H的增加,比热跃变受到抑制,并向低温方向移动,然后随着H的进一步增加,向高温方向移动。这种行为支持变磁性转变。给出了x=0和0.15晶体的详细H-T相图,并提出了可能的磁结构。磁电阻测量结果表明,$Eu^{2+}$的局域磁矩与Fe-As层中的电荷之间存在强耦合。这些结果对于理解FeAs超导体的物理基础具有重要意义。

英文摘要:

We have systematically measured resistivity, susceptibility and specific heat under different magnetic fields (H) in Eu$_{1-x}$La$_x$Fe$_2$As$_2$ single crystals. It is found that a metamagnetic transition from A-type antiferromagnetism to ferromagnetism occurs at a critical field for magnetic sublattice of $Eu^{2+}$. The jump of specific heat is suppressed and shifts to low temperature with increasing H up to the critical value, then shifts to high temperature with further increasing H. Such behavior supports the metamagnetic transition. Detailed H-T phase diagrams for x=0 and 0.15 crystals are given, and possible magnetic structure is proposed. Magnetoresistance measurements indicate that there exists a strong coupling between local moment of $Eu^{2+}$ and charge in Fe-As layer. These results are very significant to understand the underlying physics of FeAs superconductors.

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