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arXiv 0902.2027cond-mat.str-elcond-mat.mtrl-sci
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LnBaMn1.96 Fe 0.04 O 5,LnBaMn1.96 Fe 0.04 O 6和LnBaMn1.96 Fe 0.04 O5.5(Ln=Y,Gd,Sm,Nd,Pr,La)中Mn位Fe置换的锰氧化物电荷和轨道有序与无序态

Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in LnBaMn1.96Fe0.04O5, LnBaMn1.96Fe0.04O6 and LnBaMn1.96Fe0.04O5.5 (Ln=Y, Gd, Sm, Nd, Pr, La)

A. I. Rykov, Y. Ueda, K. Nomura

摘要:

合成了层状锰氧化物LnBaMn_(1.96)Fe_(0.04)O_y(Ln=Y,Gd,Sm,Nd,Pr,La)(y=5,5.5和6)。在氧饱和态(y=6)下,Ln=Y,Gd,Sm在室温下呈现电荷和轨道有序,而Ln=La,Pr,Nd在室温下呈现电子无序。由于电荷和轨道的有序性,四极分裂增加了四倍。这与电荷和轨道有序的锰氧化物与无序的锰氧化物相比,减少的钙钛矿样电池的畸变的跳跃式增加一致。用Fe取代Mn的2个替代物使结构和磁性转变温度降低20 ~ 50 K。研究了40个样品的晶格参数和室温穆斯堡尔谱,这些样品的结构被细化到五个对称群:P4/mmm,P4/nmm,Pm-3 m,Icma和P2/m。绝大多数的Fe物种是未分化的穆斯堡尔谱中的大多数样品。这样的单组分光谱中的两个网站的结构解释的优先Fe对网站的Mn(III)和分段的电荷和轨道有序域。

英文摘要:

The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La) have been synthesized for y=5, 5.5 and 6. In the oxygen-saturated state (y=6) they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd, Sm, but unordered eg-electronic system for Ln=La,Pr,Nd. Fourfold increase of quadrupole splitting was observed owing to the charge and orbital ordering. This is in agreement with the jumplike increase in distortion of the reduced perovskite-like cell for the charge and orbitally ordered manganites compared to the unordered ones. Substitution of 2 percents of Mn by Fe suppresses the temperatures of structural and magnetic transitions by 20 to 50 K. Parameters of the crystal lattices and the room-temperature Mössbauer spectra were studied on forty samples whose structures were refined within five symmetry groups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fe species are undifferentiated in the Mössbauer spectra for most of the samples. Such the single-component spectra in the two-site structures are explained by the preference of Fe towards the site of Mn(III) and by the segmentation of the charge and orbitally ordered domains.

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