arXiv 2105.030442021-05cond-mat.mtrl-scicond-mat.str-el

结构无序对Nd $_{2}$ Zr $_{2}$ O $_{7}$磁性的影响

Evaluating the Effects of Structural Disorder on the Magnetic Properties of Nd$_{2}$Zr$_{2}$O$_{7}$

Eli Zoghlin, Julian Schmehr, Collin Holgate, Rebecca Dally, Yaohua Liu, Geneva Laurita, Stephen D. Wilson

备注：: 12 pages, 10 figures
发表信息：: Phys. Rev. Materials 5, 084403 (2021)
DOI：: 10.1103/PhysRevMaterials.5.084403

摘要：

受浮区生长Nd $_{2}$ Zr $_{2}$ O $_{7}$晶体晶格参数变化的影响，我们对合成环境、结构无序和磁性能之间的关系进行了详细的研究。使用多晶标准，电子探针显微分析和散射技术的组合，我们表明，在大气条件下生长的晶体具有降低的晶格参数-相对于原始的多晶粉末-由于过量的Zr（即“负”填料）的Nd-网站的占领。与此相反，在高压Ar下生长的晶体是近化学计量的平均晶格参数接近多晶值。虽然观察到的平均结构的尺度上的氧亚晶格的最小的无序，中子对分布函数分析表明，一个高度本地的氧配位，这是只有弱依赖于生长环境的无序。最重要的是，我们的磁化强度，热容量和单晶中子散射数据表明，在高压Ar下生长的晶体的磁性能与化学计量比的粉末密切匹配。中子散射测量结果表明，磁矩碎裂的签名-共存的全进全出（AIAO）的磁布拉格峰和扩散夹点散射由于自旋冰的相关性-坚持在这些近化学计量的晶体。然而，除了增加的AIAO转变温度之外，扩散信号似乎是稳定的，并且在升温至800 mK时几乎保持不变。这一行为表明，无论是AIAO磁序和自旋冰的相关性是敏感的Nd化学计量的偏差。

英文摘要：

Motivated by the variation in reported lattice parameters of floating-zone-grown Nd$_{2}$Zr$_{2}$O$_{7}$ crystals, we have performed a detailed study of the relationship between synthesis environment, structural disorder, and magnetic properties. Using a combination of polycrystalline standards, electron-probe microanalysis and scattering techniques, we show that crystals grown under atmospheric conditions have a reduced lattice parameter - relative to pristine polycrystalline powders - due to occupation of the Nd-site by excess Zr (i.e. "negative" stuffing). In contrast, crystals grown under high-pressure Ar are nearly stoichiometric with an average lattice parameter approaching the polycrystalline value. While minimal disorder of the oxygen sublattices is observed on the scale of the average structure, neutron pair-distribution function analysis indicates a highly local disorder of the oxygen coordination, which is only weakly dependent on growth environment. Most importantly, our magnetization, heat capacity and single-crystal neutron scattering data show that the magnetic properties of crystals grown under high-pressure Ar match closely with those of stoichiometric powders. Neutron scattering measurements reveal that the signature of magnetic moment fragmentation - the coexistence of all-in-all-out (AIAO) magnetic Bragg peaks and diffuse pinch-point scattering due to spin-ice correlations - persists in these nearly stoichiometric crystals. However, in addition to an increased AIAO transition temperature, the diffuse signal is seemingly stabilized and remains nearly unchanged upon warming to 800 mK. This behavior indicates that both the AIAO magnetic order and spin-ice correlations are sensitive to deviations of the Nd stoichiometry.

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