Magnetic phase diagram of CeAu2Ge2: High magnetic anisotropy due to crystal electric field
Magnetic phase diagram of CeAu2Ge2: High magnetic anisotropy due to crystal electric field
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DOI：
10.1103/physrevb.84.104446
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发表时间：
2011-09-30
影响因子：
3.7
通讯作者：
v Loehneysen, H.
中科院分区：
文献类型：
--
作者：
Fritsch, V.;Pfundstein, P.;v Loehneysen, H.
在Au-Ge助熔剂（AGF）和Sn助熔剂（SF）中生长了CeAu_2Ge_2（具有四元ThCr_2Si_2结构）单晶。X射线粉末衍射和EDX测量表明，在后一种情况下，Sn原子从助焊剂被纳入到样品中，导致晶格常数减少约0.3%，相比AGF样品。对于这两种类型的样品，对于平行于和垂直于c方向的磁场B，观察到磁化强度M的强各向异性，在略高于10 K的低场中，M-平行于/M-垂直于约6-7。这种各向异性被保存到高场和温度，可以定量地解释晶体电场效应。反铁磁有序集在10 K左右，如以前发现的多晶样品。根据我们的单晶的磁化强度数据，我们获得了AGF和SF样品的相图。磁性能强烈地依赖于所使用的磁通量。虽然AGF样品表现出复杂的行为，指示几个磁性转变，SF样品采用了一个简单的反铁磁结构与一个单一的自旋翻转过渡。由Sn杂质形式的无序诱导的更有序状态的这种效应在各向异性次近邻伊辛（ANNNI）模型内被定性地解释，该模型假设铁磁和反铁磁相互作用与Loidl等人先前从多晶CeAu 2 Ge 2的中子散射实验中推断的磁结构一致[Phys. Rev. B 46，9341（1992）]。
CeAu2Ge2 single crystals (with tetragonal ThCr2Si2 structure) have been grown in Au-Ge flux (AGF) as well as in Sn flux (SF). X-ray powder diffraction and EDX measurements indicate that in the latter case, Sn atoms from the flux are incorporated in the samples, leading to a decrease of the lattice constants by approximate to 0.3% compared to AGF samples. For both types of samples, a strong anisotropy of the magnetization M for the magnetic field B parallel and perpendicular to the c direction is observed with M-parallel to/M-perpendicular to approximate to 6-7 in low fields just above 10 K. This anisotropy is preserved to high fields and temperatures and can be quantitatively explained by crystal electric field effects. Antiferromagnetic ordering sets in around 10 K as previously found for polycrystalline samples. From the magnetization data of our single crystals we obtain the phase diagrams for the AGF and SF samples. The magnetic properties depend strongly on the flux employed. While the AGF samples exhibit a complex behavior indicative of several magnetic transitions, the SF samples adopt a simpler antiferromagnetic structure with a single spin-flop transition. This effect of a more ordered state induced by disorder in form of Sn impurities is qualitatively explained within the anisotropic next-nearest neighbor Ising (ANNNI) model, which assumes ferromagnetic and antiferromagnetic interactions in agreement with the magnetic structure previously inferred from neutron-scattering experiments on polycrystalline CeAu2Ge2 by Loidl et al. [Phys. Rev. B 46, 9341 (1992)].