Gretarsson H, Saha S R, Drye T, Paglione J, Kim Jungho, Casa D, Gog T, Wu W, Julian S R, Kim Young-June
Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada.
Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev Lett. 2013 Jan 25;110(4):047003. doi: 10.1103/PhysRevLett.110.047003. Epub 2013 Jan 24.
We report an Fe Kβ x-ray emission spectroscopy study of local magnetic moments in the rare-earth doped iron pnictide Ca(1-x)RE(x)Fe(2)As(2) (RE = La, Pr, and Nd). In all samples studied the size of the Fe local moment is found to decrease significantly with temperature and goes from ∼ 0.9 μ(B) at T = 300 K to ∼ 0.45 μ(B) at T = 70 K. In the collapsed tetragonal phase of Nd- and Pr-doped samples (T<70 K) the local moment is quenched, while the moment remains unchanged for the La-doped sample, which does not show lattice collapse. Our results show that Ca(1-x)RE(x)Fe(2)As(2) (RE = Pr and Nd) exhibits a spin-state transition and provide direct evidence for a nonmagnetic Fe(2+) ion in the collapsed tetragonal phase; spin state as predicted by Yildirim. We argue that the gradual change of the spin state over a wide temperature range reveals the importance of multiorbital physics, in particular the competition between the crystal field split Fe 3d orbitals and the Hund's rule coupling.
我们报道了一项关于稀土掺杂铁基磷化物Ca(1-x)RE(x)Fe(2)As(2)（RE = La、Pr和Nd）中局域磁矩的Fe Kβ x射线发射光谱研究。在所研究的所有样品中，发现Fe局域磁矩的大小随温度显著减小，从T = 300 K时的约0.9 μ(B)降至T = 70 K时的约0.45 μ(B)。在Nd和Pr掺杂样品的塌缩四方相中（T<70 K），局域磁矩被淬灭，而对于未表现出晶格塌缩的La掺杂样品，磁矩保持不变。我们的结果表明，Ca(1-x)RE(x)Fe(2)As(2)（RE = Pr和Nd）表现出自旋态转变，并为塌缩四方相中存在非磁性Fe(2+)离子提供了直接证据；正如Yildirim所预测的自旋态。我们认为，自旋态在很宽温度范围内的逐渐变化揭示了多轨道物理的重要性，特别是晶体场分裂的Fe 3d轨道与洪德规则耦合之间的竞争。
