Composition-induced transition of spin-modulated structure into a uniform antiferromagnetic state in a Bi1−xLaxFeO3 system studied using 57Fe NMR
Composition-induced transition of spin-modulated structure into a uniform antiferromagnetic state in a Bi1−xLaxFeO3 system studied using 57Fe NMR
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DOI：
10.1134/1.1537425
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发表时间：
2003
影响因子：
0.6
通讯作者：
A. Zalesskiǐ;A. A. Frolov-A.;T. A. Khimich;A. Bush
中科院分区：
文献类型：
--
作者：
A. Zalesskiǐ;A. A. Frolov-A.;T. A. Khimich;A. Bush
通过对核磁共振线形的分析，研究了BiFeO_3中空间自旋调制磁结构在Bi1-−_xLa_xFeO_3固溶体中向LaFeO_3铁氧体普通空间均匀结构的转变。用自旋回波技术在77和4.2K温度下对成分为x=0、0.1、0.2、0.61、0.9和1.0的陶瓷进行了测量。结果表明，自旋调制结构在x=0.2时消失，根据已发表的数据，这对应于晶胞对称性发生变化的相变R3c→C222。得到了考虑局域线宽的自旋调制结构的核磁共振吸收线形公式。理论光谱很好地描述了实验光谱在0≤x≤0.2浓度范围内的演化。中间组合物中高度不均匀的局部磁场使得在x=0.61的样品中检测到核磁共振信号是不可能的。在纯正铁氧体LaFeO_3的非典型对称性相存在的范围内，出现了以单一窄线为特征的均匀磁结构。
By analyzing the NMR line shape, the transformation of a spatially spin-modulated magnetic structure in BiFeO3into an ordinary spatially uniform structure of the LaFeO3orthoferrite in Bi1−xLaxFeO3solid solutions is studied. The measurements are made using a spin-echo technique at temperatures of 77 and 4.2 K on ceramics with compositionsx=0, 0.1, 0.2, 0.61, 0.9, and 1.0 enriched by the57Fe isotope. It is shown that the spin-modulated structure disappears near the concentrationx=0.2, which corresponds, according to the published data, to the phase transition with a change in the unit-cell symmetryR3c→C222. A formula is obtained describing the NMR absorption line shape for the spin-modulated structure with account of local line-width. Theoretical spectra adequately describe the evolution of the experimental spectrum in the concentration range 0≤x≤0.2. Highly nonuniform local magnetic fields in the intermediate compositions make it impossible to detect NMR signals in a sample withx=0.61. A uniform magnetic structure characterized by a single narrow line arises in the range of existence of a phase with the symmetryPnmatypical of the pure orthoferrite LaFeO3.