Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study

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• 作者：Corey M. Thompson ; John E. Greedan ; V. Ovidiu Garlea ; Roxana Flacau ; Malinda Tan ; Phuong-Hieu T. Nguyen ; Friederike Wrobel ; Shahab Derakhshan
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 21, 2014
• 年：2014
• 卷：53
• 期：2
• 页码：1122-1127
• 全文大小：441K
• ISSN：1520-510X

文摘

The novel iron-based compound, BaYFeO₄, crystallizes in the Pnma space group with two distinct Fe³⁺ sites, that are alternately corner-shared [FeO₅]^7- square pyramids and [FeO₆]^9- octahedra, forming into [Fe₄O₁₈]^24- rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, ¹/₃), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe³⁺ are only of the order 3.0 渭_B, smaller than the expected values near 4.5 渭_B, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.