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首页> 外文期刊>Physical review >Magnetic hyperfine interactions on Cd sites of the rare-earth cadmium compounds RCd (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)
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Magnetic hyperfine interactions on Cd sites of the rare-earth cadmium compounds RCd (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)

机译：稀土镉化合物RCd（R = Ce，Pr，Nd，Sm，Gd，Tb，Dy，Ho和Er）在Cd位置上的磁性超精细相互作用

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摘要

This paper reports the investigation of the magnetic hyperfine field B_(hf) in a series of rare-earth (R) cadmium intermetallic compounds RCd and GdCd_2 measured by perturbed angular correlation (PAC) spectroscopy using ~(111)In/~(111)Cd as probe nuclei at Cd sites as well as first-principles calculations of B_(hf) at Cd sites in the studied compounds. Vapor-solid state reaction of R metals with Cd vapor and the ~(111)In radioisotope was found to be an appropriate route of doping rare-earth cadmium compounds with the PAC probe ~(111)In/~(111)Cd. The observation that the hyperfine parameters depend on details of the sample preparation provides information on the phase preference of diffusing ~(111)In in the rare-earth cadmium phase system. The ~(111)Cd hyperfine field has been determined in the compounds RCd for the R constituents Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, in several cases as a function of temperature. For most R constituents, the temperature dependence B_(hf)(T) of ~(111)Cd:RCd is consistent with ferromagnetic order of the compound. DyCd, however, presents a remarkable anomaly: a finite magnetic hyperfine field is observed only in the temperature interval 35 K ≤ T ≤ 80 K which indicates a transition from ferromagnetic order to a spin arrangement where all 4 f-induced contributions to the magnetic hyperfine field at the Cd site cancel. First-principles calculation results for DyCd show that the (π, π, 0) antiferromagnetic configuration is energetically more favorable than the ferromagnetic. The approach used in the calculations to simulate the RCd system successfully reproduces the experimental values of B_(hf) at Cd sites and shows that the main contribution to B_(hf) comes from the valence electron polarization. The de Gennes plot of the hyperfine field B_(hf) of ~(111)Cd:RCd vs the 4f-spin projection (g - 1)J reflects a decrease of the strength of indirect 4f-4f exchange across the R series. Possible mechanisms are discussed and the experimental results indicate that the indirect coupling is provided by the intra-atomic 4f-5d exchange and interatomic 5d-5d interaction between the spin-polarized 5d electrons of neighboring R atoms. The ratio of the hyperfine fields of GdCd and GdCd_2 scales with the number of nearest Gd neighbors. In the paramagnetic phases of the RCd compounds, the PAC spectra indicate the presence of a broad distribution of weak quadrupole interactions suggesting a perturbation of the cubic CsCl symmetry of the Cd site, most probably due to chemical disorder of the R and Cd sublattices. A substantial interchange of R and Cd atoms is also reflected in the temperature dependence of the linewidth of the magnetic hyperfine interaction in the magnetically ordered phase of RCd and GdCd_2. Its critical increase towards the order temperature is evidence for a distribution of the order temperature with a width of about 10 K.
机译：本文报道了通过〜（111）In /〜（111）扰动角相关（PAC）光谱法测量的一系列稀土（R）镉金属间化合物RCd和GdCd_2中的超精细磁场B_（hf）的研究。 Cd作为Cd位点的探针核，以及在研究化合物中Cd位点B_（hf）的第一性原理计算。发现R金属与Cd蒸气和〜（111）In放射性同位素的气固反应是用PAC探针〜（111）In /〜（111）Cd掺杂稀土镉化合物的合适途径。超细参数取决于样品制备细节的观察提供了关于在稀土镉相系统中扩散〜（111）In的相偏好的信息。在某些情况下，已经确定了化合物RCd中R成分Ce，Pr，Nd，Sm，Gd，Tb，Dy，Ho和Er的〜（111）Cd超精细场，它是温度的函数。对于大多数R成分，〜（111）Cd：RCd的温度依赖性B_（hf）（T）与化合物的铁磁顺序一致。然而，DyCd表现出明显的异常：仅在35 K≤T≤80 K的温度区间内观察到有限的磁场超精细场，这表明从铁磁有序到自旋排列的转变，其中所有4 f诱导的对磁超精细的贡献Cd网站上的字段取消。 DyCd的第一性原理计算结果表明，（π，π，0）反铁磁结构在能量上比铁磁更有利。计算中用于模拟RCd系统的方法成功地重现了Cd位置的B_（hf）实验值，并表明对B_（hf）的主要贡献来自价电子极化。 〜（111）Cd：RCd的超精细场B_（hf）与4f自旋投影（g-1）J的de Gennes图反映了R系列中间接4f-4f交换强度的降低。讨论了可能的机制，实验结果表明，间接耦合是由相邻R原子的自旋极化5d电子之间的原子内4f-5d交换和原子间5d-5d相互作用提供的。 GdCd和GdCd_2的超精细场的比例与最近的Gd邻居数成比例。在RCd化合物的顺磁性相中，PAC光谱表明存在弱四极相互作用的广泛分布，这表明Cd位置的立方CsCl对称性受到干扰，这很可能是由于R和Cd亚晶格的化学无序所致。 R和Cd原子的实质互换也反映在RCd和GdCd_2的磁性有序相中磁性超精细相互作用的线宽的温度依赖性上。它对阶温度的临界增加是阶温度分布约为10 K的证据。

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  • 来源
    《Physical review》 |2016年第6期|064417.1-064417.12|共12页
  • 作者

    F. H. M. Cavalcante; O. F. L. S. Leite Neto; H. Saitovitch; J. T. P. D. Cavalcante; A. W. Carbonari; R. N. Saxena; B. Bosch-Santos; L. F. D. Pereira; J. Mestnik-Filho; M. Forker;

  • 作者单位

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil, Department of Electrical and Computer Engineering at Colorado State University, Fort Collins, Colorado, USA;

    Centro Brasileiro de Pesquisas Fisicas - CBPF/MCTI, Rio de Janeiro, Brazil, Instituto de Engenharia Nuclear - IEN/CNEN, Rio de Janeiro, Brazil,Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Centro Brasileiro de Pesquisas Fisicas - CBPF/MCTI, Rio de Janeiro, Brazil;

    Centro Brasileiro de Pesquisas Fisicas - CBPF/MCTI, Rio de Janeiro, Brazil;

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN, Universidade de Sao Paulo, Sao Paulo, SP, Brazil;

    Centro Brasileiro de Pesquisas Fisicas - CBPF/MCTI, Rio de Janeiro, Brazil, Helmholtz Institut fuer Strahlen- und Kernphysik - Universitaet Bonn, Bonn, Germany;

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