NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC AND ORBITAL ORDERING IN 154SMNIO3 AND 153EUNIO3
NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC AND ORBITAL ORDERING IN 154SMNIO3 AND 153EUNIO3
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154SMNIO3和153EUNIO3磁序和轨道序的中子衍射研究
DOI：
10.1103/physrevb.57.456
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发表时间：
1998
影响因子：
3.7
通讯作者：
V. Trounov
中科院分区：
文献类型：
--
作者：
J. Rodríguez;S. Rosenkranz;M. Medarde;P. Lacorre;M. Fernández;F. Fauth;V. Trounov
对154SmNiO3和153EuNiO3在不同温度下进行了中子粉衍射实验。与 Pr 和 Nd 镍酸盐的情况不同，这些化合物中的金属-绝缘体转变温度与尼尔温度不同（Sm 的 TM−I ≈ 400K，TN ≈ 230K，Eu 的 TM−I ≈ 480K，TN ≈ 220K），因此在绝缘基体中冷却时会产生磁有序。随着温度降低，晶体结构在 TM−I 处经历 0.15% 的晶格膨胀。晶体对称性Pbnm在实验误差范围内没有变化，但在绝缘状态下Ni-O平均距离增加，超交换角Ni-O-Ni略有减小。两种化合物的磁结构具有与在 Pr 和 Nd 镍酸盐中观察到的相同的传播矢量 k=(1/2,0,1/2)。这一特征使我们推测，导致磁结构的轨道排序是 RNiO3 系列绝缘态的特征（至少对于轻稀土 R 而言）。对表征轨道有序性的小型核上层结构峰的搜索尚未成功。我们的实验结果的后果是在当前关于氧化物超交换的想法的背景下讨论的。
Neutron-powder-diffraction experiments on 154SmNiO3 and 153EuNiO3 at different temperatures have been performed. At variance with the case of Pr and Nd nickelates, the metal-insulator transition temperature in these compounds are different from the Neel temperature (TM−I≈400K, TN≈230K for Sm and TM−I≈480K, TN≈220K for Eu) so that the magnetic ordering develops upon cooling in an insulating matrix. With decreasing temperature the crystal structure undergoes a 0.15% lattice expansion at TM−I. The crystal symmetry Pbnm does not change within the experimental error, but the Ni-O average distance increases and the superexchange angle Ni-O-Ni decreases slightly in the insulating regime. The magnetic structure of both compounds has the same propagation vector k=(1/2,0,1/2) as observed in Pr and Nd nickelates. This feature leads us to speculate that the orbital ordering responsible for the magnetic structure is a characteristic of the insulating state of the RNiO3 series (at least for light rare earths R). A search for small nuclear superstructure peaks characterizing the orbital ordering has been carried out without success. The consequences of our experimental results are discussed in the context of current ideas about superexchange in oxides.