• Journal of Inorganic Materials
  • Vol. 36, Issue 8, 865 (2021)
Jingsan HU1, Jianfei GU1, and Weiyi ZHANG1、2、*
Author Affiliations
  • 11. School of Physics, Nanjing University, Nanjing 210093, China
  • 22. National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
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    DOI: 10.15541/jim20200623 Cite this Article
    Jingsan HU, Jianfei GU, Weiyi ZHANG. Mechanism of the Magnetic and Specific-heat Anomalies in Rare-earth Dodecaborides RB12 (R=Tb-Tm): an Effect of Crystal-field-splitting Order Parameter [J]. Journal of Inorganic Materials, 2021, 36(8): 865 Copy Citation Text show less

    Abstract

    Rare-earth dodecaborides RB12 (R=Tb, Dy, Ho, Er, Tm) are all characterized by a controversial and unresolved magnetic and specific-heat anomaly at low temperature (TC≈3-22 K) except LuB12 with closed f-shell. Although the bump feature in magnetic susceptibilities resembles that of antiferromagnetically ordered R3+ ions, no definite magnetic structure was identified by either neutron scattering or Mössbauer spectra. The anomalies in susceptibilities, entropy, and low temperature neutron diffraction pattern all pointed to the amplitude-modulated nature of complex magnetic structure. In view of the rather small crystal-field-splitting energies of the order of meV, we propose to treat crystal-field-splitting (CFS) energy as an order parameter rather than a quantum mechanical quantity. In this way, we found that not only the magnetic and specific-heat anomalies can be explained properly by a gradual quenching of R orbital moments, but also the low temperature satellite peaks of neutron scattering spectra can be understood in terms of the spontaneously (111) dimerised structure and inelastically absorbed rattling phonon modes.
    $\begin{matrix} {{H}_{0}}={{H}_{\text{SO}}}+{{H}_{\text{CF}}}+{{H}_{\text{ZS}}} \\ \end{matrix}$

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    $\begin{align} & {{Y}_{\text{l{m}'}}}{\sigma }'|{{H}_{\text{SO}}}|{{Y}_{\text{lm}}}\sigma =0.5\xi [\sqrt{(l-\sigma m)(l+\sigma m+1)} \\ & \ \ \ \ {{\delta }_{{m}'m+\sigma }}{{\delta }_{{\sigma }'\bar{\sigma }}}+\sigma m{{\delta }_{{m}'m}}{{\delta }_{{\sigma }'\sigma }}] \\ \end{align}$

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    $\begin{align} & \langle {{Y}_{\text{l{m}'}}}{\sigma }'|{{H}_{\text{ZS}}}|{{Y}_{\text{lm}}}\sigma \rangle =-{{\mu }_{\text{B}}}B\cdot \\ & \ \ \ \ [0.5({{n}_{x}}-i{{n}_{y}})\sqrt{(l-m)(l+m+1)}{{\delta }_{{m}'m+1}}{{\delta }_{{\sigma }'\sigma }}+ \\ & \ \ \ \ 0.5({{n}_{x}}+i{{n}_{y}})\sqrt{(l+m)(l-m+1)}{{\delta }_{{m}'m-1}}{{\delta }_{{\sigma }'\sigma }}+ \\ & \ \ \ \ ({{n}_{x}}+i\sigma {{n}_{y}}){{\delta }_{{m}'m}}{{\delta }_{{\sigma }'\bar{\sigma }}}+{{n}_{z}}\left( m+\sigma \right){{\delta }_{{m}'m}}{{\delta }_{{\sigma }'\sigma }}] \\ \end{align}$

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    $\begin{matrix} {{H}_{\text{CF}}}=\underset{i=1,\sigma }{\overset{7}{\mathop \sum }}\,{{J}_{i}}f_{i\sigma }^{\dagger }{{f}_{i\sigma }} \\ \end{matrix}$

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    $\begin{align} & V(\overset{\scriptscriptstyle\rightharpoonup}{r})=\frac{\alpha {{e}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}a}+\frac{280Z{{e}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}{{a}^{5}}}\left[ ({{x}^{4}}+{{y}^{4}}+{{z}^{4}})-\frac{3}{5}{{r}^{4}} \right]- \\ & \ \ \ \ \frac{1344Z{{e}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}{{a}^{7}}}\left[ ({{x}^{6}}+{{y}^{6}}+{{z}^{6}})+\ \frac{15}{4}({{x}^{2}}{{y}^{4}}+{{y}^{2}}{{z}^{4}}+ \right. \\ & \ \ \ \ \left. {{z}^{2}}{{x}^{4}}+{{x}^{2}}{{z}^{4}}+{{y}^{2}}{{x}^{4}}+{{z}^{2}}{{y}^{4}})-\frac{15}{14}{{r}^{6}} \right]~ \\ \end{align}$

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    $\begin{matrix} \text{ }\!\!\Delta\!\!\text{ }_{1}^{0}=\frac{2Z{{\text{e}}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}a}\left[ \frac{560}{33}\frac{\langle {{r}^{4}}\rangle }{{{a}^{4}}}-\frac{6720}{143}\frac{\langle {{r}^{6}}\rangle }{{{a}^{6}}} \right]~ \\ \end{matrix}$

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    $\begin{matrix} \text{ }\!\!\Delta\!\!\text{ }_{2}^{0}=\frac{2Z{{\text{e}}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}a}\left[ \frac{336}{11}\frac{\langle {{r}^{4}}\rangle }{{{a}^{4}}}-\frac{2240}{143}\frac{\langle {{r}^{6}}\rangle }{{{a}^{6}}} \right]~ \\ \end{matrix}$

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    $\begin{matrix} \Delta V=\frac{Z}{N}\frac{{\alpha }'{{\text{e}}^{2}}}{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}}\frac{2}{\sqrt{3}}\frac{Q}{{{a}^{2}}} \\ \end{matrix}$

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    $\begin{matrix} {{T}_{\text{C}}}\approx N{{\theta }_{\text{D}}}\sqrt{\frac{2{{k}_{\text{B}}}{{\theta }_{\text{D}}}{{M}_{\text{R}{{\text{B}}_{12}}}}}{{{\hbar }^{2}}{{(2\text{ }\!\!\pi\!\!\text{ }/a)}^{2}}}}\frac{4\text{ }\!\!\pi\!\!\text{ }{{\epsilon }_{0}}a}{Z{\alpha }'{{e}^{2}}}\text{ }\!\!\Delta\!\!\text{ }_{2}^{0} \\ \end{matrix}$

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    $\begin{matrix} \langle r_{i}^{n}\rangle \to {{\left[ 1+\beta \frac{{{a}_{i}}-{{a}_{\text{Tm}}}}{\sqrt[n]{\langle r_{i}^{n}\rangle }}+\gamma \right]}^{n}}\langle r_{i}^{n}\rangle \\ \end{matrix}$

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    $\begin{matrix} \text{ }\!\!\chi\!\!\text{ }_{n}^{N}=\frac{{{\mu }_{\text{B}}}}{B}\frac{\sum\limits_{I}^{C_{14}^{N}}{\mu _{I}^{N}\text{exp(}-E_{I}^{N}/{{k}_{\text{B}}}T\text{)}}}{\sum\limits_{I}^{C_{14}^{N}}{\text{exp}(-E_{I}^{N}/{{k}_{\text{B}}}T)}} \\ \end{matrix}$

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    $C_{V}^{N}=\frac{1}{{{k}_{\text{B}}}{{T}^{2}}}\left\{ \frac{\sum\limits_{I}^{C_{14}^{N}}{{{(E_{I}^{N})}^{2}}\exp (-E_{I}^{N}/{{k}_{\text{B}}}T)}}{\sum\limits_{I}^{C_{14}^{N}}{\exp (-E_{I}^{N}/{{k}_{\text{B}}}T)}}- \right.\ \left. {{\left[ \frac{\sum\limits_{I}^{C_{14}^{N}}{E_{I}^{N}\exp (-E_{I}^{N}/{{k}_{\text{B}}}T)}}{\sum\limits_{I}^{C_{14}^{N}}{\exp (-E_{I}^{N}/{{k}_{\text{B}}}T)}} \right]}^{2}} \right\}$

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    Jingsan HU, Jianfei GU, Weiyi ZHANG. Mechanism of the Magnetic and Specific-heat Anomalies in Rare-earth Dodecaborides RB12 (R=Tb-Tm): an Effect of Crystal-field-splitting Order Parameter [J]. Journal of Inorganic Materials, 2021, 36(8): 865
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