Neutron Diffraction and Isotropic Volume Expansion Caused by Deuterium Absorption into La(Fe_<0.88>Si_<0.12>)_<13>(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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The crystal structures and magnetic properties of La(Fe_<0.88>Si_<0.12>)_<13>D_<1.5> and L(Fe_<0.88>Si_<0.12>)_<13>H_<1.6> have been investigated. The powder neutron diffraction declared that the compound La(Fe_<0.88>Si_<0.12>)_<13>D_<1.5> has a cubic NaZn_<13>-type structure of the Fm3^^-c space group in analogy with La(Fe_<0.88>Si_<0.12>)_<13>. The deuterium atoms in the compound La(Fe_<0.88>Si_<0.12>)_<13>D_<1.5> occupy the interstitial 24d site surrounded by two La atoms and four icosahedral clusters. The x-ray diffraction data of La(Fe_<0.88>Si_<0.12>)_<13>H_<1.6> are also consistently explained by the same site of hydrogen atom. The deuterium or hydrogen absorption brings out a notable increase of the Curie temperature T_C. The neutron diffraction of the compound La(Fe_<0.88>Si_<0.12>)_<13>D_<1.5> shows that the magnetic structure is ferromagnetic and the average magnetic moment per Fe is about 2.2μ_B, almost the same as that of La(Fe_<0.88>Si_<0.12>)_<13>. Such behaviors can be explained as characteristic magnetovolume effects in itinerant-electron metamagnets. That is, when the hydrogen or deuterium atom at the 24d site causes the isotropic volume expansion, the magnetic free energy curve with a double minimum structure renormalized by spin fluctuations induces a marked increase of T_C without a pronounced increase of the magnetic moment.
社団法人日本物理学会の論文
2008-07-15